9780141983769

P EN GUIN P RES S WH Y WE S L EEP

The International Bestseller

‘A neuroscientist shows how a good night’s shut-eye can make us cleverer, more attractive, slimmer, happier, healthier and ward off cancer … it’s probably a little too soon to tell you that it saved my life, but it’s been an eye-opener’

‘Startling, vital, a life raft’ G U A R D I A N

S P IN E WIDT H : 21 M M

‘Passionate, urgent … it had a powerful effect on me’ R ACHEL COOKE, OB SERVER

‘Compelling and utterly convincing … you’ll never think of your bedtime in the same way again’ J A M E S M C C O N N A C H I E , T H E S U N D AY T I M E S

‘A stimulating and important book … richly packed with science’ CLIVE COOKSON, FINANCIAL TIMES

‘Uplifting … Walker is in love with sleep and wants us to fall in love with sleep, too’

MAT THEW WALKER WHY WE SLEEP

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Date: 06/12/2017 Designer: Æ Prod. Controller: Pub. Date: ISBN: 9780141983769

ALLEN PENGUIN LANE Health/Science BOOK

06/12/2017 15:46

PART 1 ✦

This Thing Called Sleep

CHAPTER CHAPTER11

To ToSleep . . .

Sleep . . .

Do Doyou youthink thinkyou yougot gotenough enoughsleep sleepthis thispast pastweek? week?Can Canyou yourecall recall the thelast lasttime timeyou youwoke wokeup upwithout withoutan analarm alarmclock clockfeeling feelingrefreshed, refreshed, not notneeding needingcaffeine? caffeine?IfIfthe theanswer answertotoeither eitherofofthese thesequestions questionsisis “no, “no,” ”you youare arenot notalone. alone.More Morethan thanaathird thirdofofadults adultsininmany manydeveldeveloped opednations nationsfail failtotoobtain obtainthe therecommended recommendedseven seventotonine ninehours hoursofof nightly nightlysleep.* sleep.* I Idoubt doubtyou youare aresurprised surprisedby bythis thisfact, fact,but butyou youmay maybe besurprised surprisedby bythe the consequences. consequences.Routinely Routinelysleeping sleepingless lessthan thansix sixhours hoursaanight nightweakens weakens your yourimmune immunesystem, system,substantially substantiallyincreasing increasingyour yourrisk riskofofcertain certainforms forms ofofcancer. cancer.Insufficient Insufficientsleep sleepappears appearstotobe beaakey keylifestyle lifestylefactor factorlinked linked totoyour yourrisk riskofofdeveloping developingAlzheimer’s Alzheimer’sdisease. disease.Inadequate Inadequatesleep—even sleep—even moderate moderatereductions reductionsfor forjust justone oneweek—disrupts week—disruptsblood bloodsugar sugarlevels levelsso so profoundly profoundlythat thatyou youwould wouldbe beclassified classifiedasaspre-diabetic. pre-diabetic.Short Shortsleeping sleeping increases increasesthe thelikelihood likelihoodofofyour yourcoronary coronaryarteries arteriesbecoming becomingblocked blockedand and brittle, brittle,setting settingyou youon onaapath pathtoward towardcardiovascular cardiovasculardisease, disease,stroke, stroke,and and congestive congestiveheart heartfailure. failure.Fitting FittingCharlotte CharlotteBrontë’s Brontë’sprophetic propheticwisdom wisdom that that“a“aruffled ruffledmind mindmakes makesaarestless restlesspillow, pillow, ” ”sleep sleepdisruption disruptionfurther further contributes contributestotoall allmajor majorpsychiatric psychiatricconditions, conditions,including includingdepression, depression, anxiety, anxiety,and andsuicidality. suicidality.

Perhaps Perhapsyou youhave havealso alsonoticed noticedaadesire desiretotoeat eatmore morewhen whenyou’re you’re tired? tired?This Thisisisno nocoincidence. coincidence.Too Toolittle littlesleep sleepswells swellsconcentrations concentrations ofofaahormone hormonethat thatmakes makesyou youfeel feelhungry hungrywhile whilesuppressing suppressingaacomcom*The *TheCenters Centersfor forDisease DiseaseControl Control(CDC) (CDC)stipulates stipulatesthat thatadults adultsneed needseven sevenhours hoursofofsleep sleep orormore moreper pertwenty-four twenty-fourhours. hours.

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panion panionhormone hormonethat thatotherwise otherwisesignals signalsfood foodsatisfaction. satisfaction.Despite Despite being beingfull, full,you youstill stillwant wanttotoeat eatmore. more.It’s It’saaproven provenrecipe recipefor forweight weight gain gainininsleep-deficient sleep-deficientadults adultsand andchildren childrenalike. alike.Worse, Worse,should shouldyou you attempt attempttotodiet dietbut butdon’t don’tget getenough enoughsleep sleepwhile whiledoing doingso, so,ititisisfutile, futile, since sincemost mostofofthe theweight weightyou youlose losewill willcome comefrom fromlean leanbody bodymass, mass, not notfat. fat.

Add Addthe theabove abovehealth healthconsequences consequencesup, up,and andaaproven provenlink linkbecomes becomes easier easiertotoaccept: accept:relative relativetotothe therecommended recommendedseven seventotonine ninehours, hours, the theshorter shorteryour yoursleep, sleep,the theshorter shorteryour yourlife lifespan. span.The Theold oldmaxim maxim“I’ll “I’ll sleep sleepwhen whenI’m I’mdead” dead”isistherefore thereforeunfortunate. unfortunate.Adopt Adoptthis thismind-set, mind-set, and andititisispossible possiblethat thatyou youwill willbe bedead deadsooner soonerand andthe thequality qualityofof that that(shorter) (shorter)life lifewill willbe beworse. worse.The Theelastic elasticband bandofofsleep sleepdeprivadeprivation tioncan canstretch stretchonly onlyso sofar farbefore beforeititsnaps. snaps.Sadly, Sadly,human humanbeings beingsare are ininfact factthe theonly onlyspecies speciesthat thatwill willdeliberately deliberatelydeprive deprivethemselves themselvesofof sleep sleepwithout withoutlegitimate legitimategain. gain.Numerous Numerouscomponents componentsofofwellness, wellness, and andcountless countlessseams seamsofofsocietal societalfabric, fabric,are arebeing beingeroded erodedby byour ourcostly costly state stateofofsleep sleepneglect: neglect:human humanand andfinancial financialalike. alike.So Somuch muchso sothat that the theCenter Centerfor forDisease DiseaseControl Controldeclared declaredinsufficient insufficientsleep sleepasasaapublic public health healthepidemic. epidemic.ItItmay maynot notbe beaacoincidence coincidencethat thatcountries countrieswhere where sleep sleep time time has has declined declined most most dramatically dramatically over over the the past past century, century, such suchasasthe theUS, US,the theUK, UK,Japan, Japan,and andSouth SouthKorea, Korea,and andseveral severalininwestwestern ernEurope, Europe,are arealso alsothose thosesuffering sufferingthe thegreatest greatestincrease increaseininrates ratesofof the theaforementioned aforementionedphysical physicaldiseases diseasesand andmental mentaldisorders. disorders.

Scientists Scientistssuch suchasasmyself myselfhave haveeven evenstarted startedlobbying lobbyingdoctors doctorstotostart start “prescribing” “prescribing”sleep. sleep.As Asmedical medicaladvice advicegoes, goes,it’s it’sperhaps perhapsthe themost mostpainpainless lessand andenjoyable enjoyabletotofollow. follow.Do Donot, not,however, however,mistake mistakethis thisasasaaplea pleatoto doctors doctorstotostart startprescribing prescribingmore moresleeping sleepingpills—quite pills—quitethe theopposite, opposite,inin fact, fact,considering consideringthe theevidence evidencesurrounding surroundingthe thedeleterious deleterioushealth healthconconsequences sequencesofofthese thesedrugs. drugs.

But Butcan canwe wego goso sofar farasastotosay saythat thataalack lackofofsleep sleepcan cankill killyou yououtright? outright?

Quite Quitepossibly—on possibly—onatatleast leasttwo twocounts. counts.First, First,there thereisisaavery veryrare raregenetic genetic disorder disorderthat thatstarts startswith withaaprogressive progressiveinsomnia, insomnia,emerging emergingininmidlife. midlife.

Several Severalmonths monthsinto intothe thedisease diseasecourse, course,the thepatient patientstops stopssleeping sleepingaltoaltogether. gether.By Bythis thisstage, stage,they theyhave havestarted startedtotolose losemany manybasic basicbrain brainand and body bodyfunctions. functions.Few Fewdrugs drugsthat thatwe wecurrently currentlyhave havewill willhelp helpthe thepatient patient sleep. sleep.After Aftertwelve twelvetotoeighteen eighteenmonths monthsofofno nosleep, sleep,the thepatient patientwill willdie. die.

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Second Secondisisthe thedeadly deadlycircumstance circumstanceofofgetting gettingbehind behindthe thewheel wheelofofaa motor motorvehicle vehiclewithout withouthaving havinghad hadsufficient sufficientsleep. sleep.Drowsy Drowsydriving drivingisisthe the cause causeofofhundreds hundredsofofthousands thousandsofoftraffic trafficaccidents accidentsand andfatalities fatalitieseach each year. year.And Andhere, here,ititisisnot notonly onlythe thelife lifeofofthe thesleep-deprived sleep-deprivedindividuals individuals that thatisisatatrisk, risk,but butthe thelives livesofofthose thosearound aroundthem. them.Tragically, Tragically,one oneperperson sondies diesininaatraffic trafficaccident accidentevery everyhour hourininthe theUnited UnitedStates Statesdue duetotoaa fatigue-related fatigue-relatederror. error.

Society’s Society’sapathy apathytoward towardsleep sleephas, has,ininpart, part,been beencaused causedby bythe thehishistoric toricfailure failureofofscience sciencetotoexplain explainwhy whywe weneed needit.it.Sleep Sleepremained remainedone one ofofthe thelast lastgreat greatbiological biologicalmysteries. mysteries.All Allofofthe themighty mightyproblem-solving problem-solving methods methodsininscience—genetics, science—genetics,molecular molecularbiology, biology,and andhigh-powered high-powered digital digitaltechnology—have technology—havebeen beenunable unabletotounlock unlockthe thestubborn stubbornvault vaultofof sleep. sleep.Minds Mindsofofthe themost moststringent stringentkind, kind,including includingNobel NobelPrize– Prize–winner winner Francis Francis Crick, Crick, who who deduced deduced the the twisted-ladder twisted-ladder structure structure ofof DNA, DNA, famed famedRoman Romaneducator educatorand andrhetorician rhetoricianQuintilian, Quintilian,and andeven evenSigmund Sigmund Freud Freudhad hadall alltried triedtheir theirhand handatatdeciphering decipheringsleep’s sleep’senigmatic enigmaticcode, code,all all ininvain. vain.

To Tobetter betterframe framethis thisstate stateofofprior priorscientific scientificignorance, ignorance,imagine imaginethe the birth birthofofyour yourfirst firstchild. child.At Atthe thehospital, hospital,the thedoctor doctorenters entersthe theroom roomand and says, says,“Congratulations, “Congratulations,it’s it’saahealthy healthybaby babyboy. boy.We’ve We’vecompleted completedall allofof the thepreliminary preliminarytests testsand andeverything everythinglooks looksgood. good. ” ”She Shesmiles smilesreassurreassuringly inglyand andstarts startswalking walkingtoward towardthe thedoor. door.However, However,before beforeexiting exitingthe the room roomshe sheturns turnsaround aroundand andsays, says,“There “Thereisisjust justone onething. thing.From Fromthis this moment momentforth, forth,and andfor forthe therest restofofyour yourchild’s child’sentire entirelife, life,he hewill willrepeatrepeatedly edlyand androutinely routinelylapse lapseinto intoaastate stateofofapparent apparentcoma. coma.ItItmight mighteven even resemble resembledeath deathatattimes. times.And Andwhile whilehis hisbody bodylies liesstill stillhis hismind mindwill willoften often be befilled filledwith withstunning, stunning,bizarre bizarrehallucinations. hallucinations.This Thisstate statewill willconsume consume one-third one-thirdofofhis hislife lifeand andI Ihave haveabsolutely absolutelyno noidea ideawhy whyhe’ll he’lldo doit,it,ororwhat what ititisisfor. for.Good Goodluck!” luck!”

Astonishing, Astonishing,but butuntil untilvery veryrecently, recently,this thiswas wasreality: reality:doctors doctorsand andsciscientists entistscould couldnot notgive giveyou youaaconsistent consistentororcomplete completeanswer answerasastotowhy why we wesleep. sleep.Consider Considerthat thatwe wehave haveknown knownthe thefunctions functionsofofthe thethree threeother other basic basicdrives drivesininlife—to life—toeat, eat,totodrink, drink,and andtotoreproduce—for reproduce—formany manytens tens ififnot nothundreds hundredsofofyears yearsnow. now.Yet Yetthe thefourth fourthmain mainbiological biologicaldrive, drive,comcommon monacross acrossthe theanimal animalkingdom—the kingdom—thedrive drivetotosleep—has sleep—hascontinued continuedtoto elude eludescience sciencefor formillennia. millennia.

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Addressing Addressingthe thequestion questionofofwhy whywe wesleep sleepfrom froman anevolutionary evolutionaryperperspective spectiveonly onlycompounds compoundsthe themystery. mystery.No Nomatter matterwhat whatvantage vantagepoint point you youtake, take,sleep sleepwould wouldappear appeartotobe bethe themost mostfoolish foolishofofbiological biologicalphephenomena. nomena.When Whenyou youare areasleep, asleep,you youcannot cannotgather gatherfood. food.You Youcannot cannot socialize. socialize.You Youcannot cannotfind findaamate mateand andreproduce. reproduce.You Youcannot cannotnurture nurture oror protect protect your your offspring. offspring. Worse Worse still, still, sleep sleep leaves leaves you you vulnerable vulnerable totopredation. predation.Sleep Sleepisissurely surelyone oneofofthe themost mostpuzzling puzzlingofofall allhuman human behaviors. behaviors.

On On any any one one ofof these these grounds—never grounds—never mind mind all all ofof them them inin combination—there combination—thereought oughttotohave havebeen beenaastrong strongevolutionary evolutionarypressure pressure totoprevent preventthe theemergence emergenceofofsleep sleepororanything anythingremotely remotelylike likeit.it.As Asone one sleep sleepscientist scientisthas hassaid, said,“If “Ifsleep sleepdoes doesnot notserve servean anabsolutely absolutelyvital vital function, function,then thenititisisthe thebiggest biggestmistake mistakethe theevolutionary evolutionaryprocess processhas has ever evermade. made. ”*”* Yet Yetsleep sleephas haspersisted. persisted.Heroically Heroicallyso. so.Indeed, Indeed,every everyanimal animalspespe†† Thissuggests suggeststhat thatsleep sleepevolved evolved cies ciescarefully carefullystudied studiedtotodate datesleeps. sleeps. This with—or with—orvery verysoon soonafter—life after—lifeitself itselfon onour ourplanet. planet.Moreover, Moreover,the thesubsubsequent sequent perseverance perseverance ofof sleep sleep throughout throughout evolution evolution means means there there must mustbe betremendous tremendousbenefits benefitsthat thatfar faroutweigh outweighall allofofthe theobvious obvioushazhazards ardsand anddetriments. detriments.

Ultimately, Ultimately,asking asking“Why “Whydo dowe wesleep?” sleep?”was wasthe thewrong wrongquestion. question.ItIt implied impliedthere therewas wasaasingle singlefunction, function,one oneholy holygrail grailofofaareason reasonthat that we weslept, slept,and andwe wewent wentininsearch searchofofit.it.Theories Theoriesranged rangedfrom fromthe thelogilogical cal(a(atime timefor forconserving conservingenergy), energy),totothe thepeculiar peculiar(an (anopportunity opportunityfor for eyeball eyeballoxygenation), oxygenation),totothe thepsychoanalytic psychoanalytic(a(anon-conscious non-consciousstate stateinin which whichwe wefulfill fulfillrepressed repressedwishes). wishes).

This Thisbook bookwill willreveal revealaavery verydifferent differenttruth: truth:sleep sleepisisinfinitely infinitelymore more complex, complex,profoundly profoundlymore moreinteresting, interesting,and andstrikingly strikinglyhealth-relevant. health-relevant.

We Wesleep sleepfor foraarich richlitany litanyofoffunctions, functions,plural—an plural—anabundant abundantconstellaconstellation tionofofnighttime nighttimebenefits benefitsthat thatservice serviceboth bothour ourbrains brainsand andour ourbodies. bodies.

There Theredoes doesnot notseem seemtotobe beone onemajor majororgan organwithin withinthe thebody, body,ororproprocess cesswithin withinthe thebrain, brain,that thatisn’t isn’toptimally optimallyenhanced enhancedby bysleep sleep(and (anddetdetrimentally rimentallyimpaired impairedwhen whenwe wedon’t don’tget getenough). enough).That Thatwe wereceive receivesuch such *Dr. *Dr.Allan AllanRechtschaffen.

Rechtschaffen. †† Cirelli, Cirelli,C., C.,and andTononi, Tononi,G.G.(2008).

(2008).IsIssleep sleepessential? essential?PLoS PLoSBiology.

Biology.6,6,e216. e216.

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aabounty bountyofofhealth healthbenefits benefitseach eachnight nightshould shouldnot notbe besurprising. surprising.After After all, all,we weare areawake awakefor fortwo-thirds two-thirdsofofour ourlives, lives,and andwe wedon’t don’tjust justachieve achieve one oneuseful usefulthing thingduring duringthat thatstretch stretchofoftime. time.We Weaccomplish accomplishmyriad myriad undertakings undertakingsthat thatpromote promoteour ourown ownwell-being well-beingand andsurvival. survival.Why, Why, then, then,would wouldwe weexpect expectsleep—and sleep—andthe thetwenty-five twenty-fivetotothirty thirtyyears, years,on on average, average,itittakes takesfrom fromour ourlives—to lives—tooffer offerone onefunction functiononly? only?

Through Throughan anexplosion explosionofofdiscoveries discoveriesover overthe thepast pasttwenty twentyyears, years,we we have havecome cometotorealize realizethat thatevolution evolutiondid didnot notmake makeaaspectacular spectacularblunder blunder ininconceiving conceivingofofsleep. sleep.Sleep Sleepdispenses dispensesaamultitude multitudeofofhealth-ensuring health-ensuring benefits, benefits, yours yours toto pick pick up up inin repeat repeat prescription prescription every every twenty-four twenty-four hours, hours,should shouldyou youchoose. choose.

Within Withinthe thebrain, brain,sleep sleepenriches enrichesaadiversity diversityofoffunctions, functions,including including our ourability abilitytotolearn, learn,memorize, memorize,and andmake makelogical logicaldecisions decisionsand andchoices. choices.

Benevolently Benevolentlyservicing servicingour ourpsychological psychologicalhealth, health,sleep sleeprecalibrates recalibratesour our emotional emotionalbrain braincircuits, circuits,allowing allowingus ustotonavigate navigatenext-day next-daysocial socialand and psychological psychologicalchallenges challengeswith withcool-headed cool-headedcomposure. composure.We Weare areeven even beginning beginningtotounderstand understandthe themost mostimpervious imperviousand andcontroversial controversialofofall all conscious consciousexperiences: experiences:the thedream. dream.Dreaming Dreamingprovides providesaaunique uniquesuite suite ofofbenefits benefitstotoall allspecies speciesfortunate fortunateenough enoughtotoexperience experienceit,it,humans humans included. included.Among Amongthese thesegifts giftsare areaaconsoling consolingneurochemical neurochemicalbath baththat that mollifies mollifiespainful painfulmemories memoriesand andaavirtual virtualreality realityspace spaceininwhich whichthe thebrain brain melds meldspast pastand andpresent presentknowledge, knowledge,inspiring inspiringcreativity. creativity.

Downstairs Downstairsininthe thebody, body,sleep sleeprestocks restocksthe thearmory armoryofofour ourimmune immune system, system,helping helpingprevent preventinfection, infection,and andwarding wardingoff offall allmanner mannerofofsicksickness. ness. Sleep Sleep reforms reforms the the body’s body’s metabolic metabolic state state by by fine-tuning fine-tuning the the balance balanceofofinsulin insulinand andcirculating circulatingglucose. glucose.Sleep Sleepfurther furtherregulates regulatesour our appetite, appetite,helping helpingcontrol controlbody bodyweight weightthrough throughhealthy healthyfood foodselection selection rather rather than than rash rash impulsivity. impulsivity. Plentiful Plentiful sleep sleep maintains maintains aa flourishing flourishing microbiome microbiomewithin withinyour yourgut gutfrom fromwhich whichwe weknow knowso somuch muchofofour ournutrinutritional tionalhealth healthbegins. begins.Adequate Adequatesleep sleepisisintimately intimatelytied tiedtotothe thefitness fitnessofof our ourcardiovascular cardiovascularsystem, system,lowering loweringblood bloodpressure pressurehelping helpingkeep keepour our hearts heartsininfine finecondition. condition.

AAbalanced balanceddiet dietand andexercise exerciseare areofofvital vitalimportance, importance,yes. yes.But Butwe we now nowsee seesleep sleepasasaapreeminent preeminentforce forceininthis thishealth healthtrinity. trinity.The Thephysiphysical caland andmental mentalimpairments impairmentscaused causedby byone onenight nightofofbad badsleep sleepdwarf dwarf those thosecaused causedby byan anequivalent equivalentabsence absenceofoffood foodororexercise. exercise.ItItisisdifficult difficult

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totoimagine imagineany anyother otherstate—natural state—naturalorormedically medicallymanipulated—that manipulated—that affords affordsaamore morepowerful powerfulredressing redressingofofphysical physicaland andmental mentalhealth healthatat every everylevel levelofofanalysis. analysis.

Based Basedon onaarich, rich,new newscientific scientificunderstanding understandingofofsleep, sleep,we weno nolonger longer have havetotoask askwhat whatsleep sleepisisgood goodfor. for.Instead, Instead,we weare arenow nowforced forcedtotowonder wonder whether whetherthere thereare areany anybiological biologicalfunctions functionsthat thatdo donot notbenefit benefitby byaagood good night’s night’ssleep. sleep.

Emerging Emergingfrom fromthis thisresearch researchrenaissance renaissanceisisan anunequivocal unequivocalmessage: message: sleep sleepisisthe thesingle singlemost mosteffective effectivething thingwe wecan cando dototoreset resetour ourbrain brainand and body bodyhealth healtheach eachday—Mother day—MotherNature’s Nature’sbest besteffort effortyet yetatatcontra-death. contra-death.

Unfortunately, Unfortunately,the thereal realevidence evidencethat thatmakes makesclear clearall allofofthe thedangers dangersthat that befall befallindividuals individualsand andsocieties societieswhen whensleep sleepbecomes becomesshort shorthave havenot not been beenclearly clearlytelegraphed telegraphedtotothe thepublic. public.ItItisisperhaps perhapsthe themost mostglaring glaring omission omissionininthe thecontemporary contemporaryhealth healthconversation. conversation.InInresponse, response,this this book bookisisintended intendedtotohelp helpaddress addressthis thisunmet unmetneed, need,and andprovide providewhat what I Ihope hopeisisaafascinating fascinatingjourney journeyofofdiscoveries. discoveries.ItItaims aimstotorevise reviseour ourculcultural turalappreciation appreciationofofsleep, sleep,and andreverse reverseour ourneglect neglectofofit.it.

Personally, Personally,I Ishould shouldnote notethat thatI Iam amrather ratherininlove lovewith withsleep sleep(not (notjust just my myown, own,though thoughI Ido dogive givemyself myselfaanon-negotiable non-negotiableeight-hour eight-hoursleep sleep opportunity opportunityeach eachnight). night).I Iam amininlove lovewith witheverything everythingsleep sleepisisand and does. does.I Iam amininlove lovewith withdiscovering discoveringall allthat thatremains remainsunknown unknownabout aboutit.it.

I Iam amininlove lovewith withcommunicating communicatingthe therelevance relevanceofofitittotothe thepublic. public.I Iam am ininlove lovewith withfinding findingany anyand andall allmethods methodsfor forreuniting reunitinghumanity humanitywith with the thesleep sleepititso sodesperately desperatelyneeds. needs.This Thislove loveaffair affairhas hasnow nowspanned spannedaa twenty-plus-year twenty-plus-yearresearch researchcareer careerthat thatbegan beganwhen whenI Iwas wasaaprofessor professor ofofpsychiatry psychiatryatatHarvard HarvardMedical MedicalSchool Schooland andcontinues continuesnow nowthat thatI I am amaaprofessor professorofofneuroscience neuroscienceand andpsychology psychologyatatthe theUniversity Universityofof California, California,Berkeley.

Berkeley.

ItItwas wasnot, not,however, however,love loveatatfirst firstsight. sight.I Iam aman anaccidental accidentalsleep sleep researcher. researcher. ItIt was was never never my my intent intent toto inhabit inhabit this this esoteric esoteric outer outer territory territoryofofscience. science.At Atage ageeighteen eighteenI Iwent wenttotostudy studyatatthe theQueen’s Queen’s Medical Medical Center Center inin England: England: aa prodigious prodigious institute institute inin Nottingham Nottingham boasting boastingaawonderful wonderfulband bandofofbrain brainscientists scientistson onits itsfaculty. faculty.Ultimately, Ultimately, medicine medicinewasn’t wasn’tfor forme, me,asasititseemed seemedmore moreconcerned concernedwith withanswers, answers,

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whereas whereasI Iwas wasalways alwaysmore moreenthralled enthralledby byquestions. questions.For Forme, me,answers answers were weresimply simplyaaway waytotoget gettotothe thenext nextquestion. question.I Idecided decidedtotostudy studyneuneuroscience, roscience,and andafter aftergraduating, graduating,obtained obtainedmy myPhD PhDininneurophysiology neurophysiology supported supportedby byaafellowship fellowshipfrom fromEngland’s England’sMedical MedicalResearch ResearchCouncil, Council, London.

London.

ItItwas wasduring duringmy myPhD PhDwork, work,conducted conductedmostly mostlyatatNewcastle NewcastleUniUniversity, versity,I Ibegan beganmaking makingmy myfirst firstscientific scientificcontributions contributionsininthe thefield field ofofsleep sleepresearch. research.I Iwas wasexamining examiningpatterns patternsofofelectrical electricalbrainwave brainwave activity activityininolder olderadults adultsininthe theearly earlystages stagesofofdementia. dementia.Counter Countertoto common commonbelief, belief,there thereisn’t isn’tjust justone onetype typeofofdementia. dementia.Alzheimer’s Alzheimer’sdisdisease easeisisthe themost mostcommon, common,but butisisonly onlyone oneofofmany manytypes. types.For Foraanumnumber berofoftreatment treatmentreasons, reasons,ititisiscritical criticaltotoknow knowwhich whichtype typeofofdementia dementia an anindividual individualisissuffering sufferingfrom fromasassoon soonasaspossible. possible.

I Ibegan beganassessing assessingbrainwave brainwaveactivity activityfrom frommy mypatients patientsduring duringwake wake and and sleep. sleep. My My hypothesis: hypothesis: there there was was aa unique unique and and specific specific electrielectrical calbrain brainsignature signaturethat thatcould couldforecast forecastwhich whichdementia dementiasubtype subtypeeach each individual individualwas wasprogressing progressingtoward. toward.Measurements Measurementstaken takenduring duringthe the day daywere wereambiguous, ambiguous,with withno noclear clearsignature signatureofofdifference differencetotobe befound. found.

Only Onlyininthe thenighttime nighttimeocean oceanofofsleeping sleepingbrainwaves brainwavesdid didthe therecordings recordings speak speakout outaaclear clearlabeling labelingofofmy mypatients patientssaddening saddeningdisease diseasefate. fate.The The discovery discoveryproved provedthat thatsleep sleepcould couldpotentially potentiallybe beused usedasasaanew newearly early diagnostic diagnosticlitmus litmustest testtotounderstand understandwhich whichtype typeofofdementia dementiaan anindiindividual vidualwould woulddevelop. develop.

Sleep Sleepbecame becamemy myobsession. obsession.The Theanswer answeritithad hadprovided providedme, me,like likeall all good goodanswers, answers,only onlyled ledtotomore morefascinating fascinatingquestions, questions,among amongthem: them:Was Was the thedisruption disruptionofofsleep sleepininmy mypatients patientsactually actuallycontributing contributingtotothe thediseases diseases they theywere weresuffering sufferingfrom, from,and andeven evencausing causingsome someofoftheir theirterrible terriblesympsymptoms, toms,such suchasasmemory memoryloss, loss,aggression, aggression,hallucinations, hallucinations,delusions? delusions?I Iread read all allI Icould. could.AAscarcely scarcelybelievable believabletruth truthbegan begantotoemerge—nobody emerge—nobodyactually actually knew knewthe theclear clearreason reasonwhy whywe weneeded neededsleep, sleep,and andwhat whatititdoes. does.I Icould couldnot not answer answermy myown ownquestion questionabout aboutdementia dementiaififthis thisfundamental fundamentalfirst firstquesquestion tionremained remainedunanswered. unanswered.I Idecided decidedI Iwould wouldtry trytotocrack crackthe thecode codeofofsleep. sleep.

I Ihalted haltedmy myresearch researchinindementia dementiaand, and,for foraapost-doctoral post-doctoralposition position that thattook tookme meacross acrossthe theAtlantic AtlanticOcean OceantotoHarvard, Harvard,set setabout aboutaddressaddressing ing one one ofof the the most most enigmatic enigmatic puzzles puzzles ofof humanity—one humanity—one that that had had eluded eludedsome someofofthe thebest bestscientists scientistsininhistory: history:Why Whydo dowe wesleep? sleep?With With

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genuine genuinenaïveté, naïveté,not nothubris, hubris,I Ibelieved believedI Iwould wouldfind findthe theanswer answerwithin within two twoyears. years.That Thatwas wastwenty twentyyears yearsago. ago.Hard Hardproblems problemscare carelittle littleabout about what whatmotivates motivatestheir theirinterrogators; interrogators;they theymeter meterout outtheir theirlessons lessonsofofdifdifficulty ficultyall allthe thesame. same.

Now, Now,after aftertwo twodecades decadesofofmy myown ownresearch researchefforts, efforts,combined combinedwith with thousands thousandsofofstudies studiesfrom fromother otherlaboratories laboratoriesaround aroundthe theworld, world,we wehave have many manyofofthe theanswers. answers.These Thesediscoveries discoverieshave havetaken takenme meon onwonderful, wonderful, privileged, privileged,and andunexpected unexpectedjourneys journeysinside insideand andoutside outsideofofacademia— academia— from frombeing beingaasleep sleepconsultant consultantfor forthe theNBA, NBA,NFL, NFL,and andBritish BritishPremier Premier League Leaguefootball footballteams; teams;totoPixar PixarAnimation, Animation,government governmentagencies, agencies,and and well-known well-knowntechnology technologyand andfinancial financialcompanies. companies.These Thesesleep sleeprevelarevelations, tions,together togetherwith withmany manysimilar similardiscoveries discoveriesfrom frommy myfellow fellowsleep sleepsciscientists, entists,will willoffer offerproof proofabout aboutthe thevital vitalimportance importanceofofsleep. sleep.

AAfinal finalcomment commenton onthe thestructure structureofofthis thisbook. book.The Thechapters chaptersare arewritten written ininaalogical logicalorder, order,traversing traversingaanarrative narrativearc arcininfour fourmain mainparts. parts.

Part Part11demystifies demystifiesthis thisbeguiling beguilingthing thingcalled calledsleep: sleep:what whatititis,is,what whatitit isn’t, isn’t,who whosleeps, sleeps,how howmuch muchthey theysleep, sleep,how howhuman humanbeings beingsshould shouldsleep sleep (but (butare arenot), not),and andhow howsleep sleepchanges changesacross acrossyour yourlife lifespan spanororthat thatofof your yourchild, child,for forbetter betterand andfor forworse. worse.

Part Part22details detailsthe thegood, good,the thebad, bad,and andthe thedeathly deathlyofofsleep sleepand andsleep sleep loss. loss.We Wewill willexplore exploreall allofofthe theastonishing astonishingbenefits benefitsofofsleep sleepfor forbrain brainand and for forbody, body,affirming affirmingwhat whataaremarkable remarkableSwiss SwissArmy Armyknife knifeofofhealth healthand and wellness wellnesssleep sleeptruly trulyis.is.Then Thenwe weturn turntotohow howand andwhy whyaalack lackofofsufficient sufficient sleep sleepleads leadstotoaaquagmire quagmireofofillillhealth, health,disease, disease,and anduntimely untimelydeath—a death—a wakeup wakeupcall calltotosleep sleepififever everthere therewas wasone. one.

Part Part33offers offerssafe safepassage passagefrom fromsleep sleeptotothe thefantastical fantasticalworld worldofof dreams dreamsscientifically scientificallyexplained. explained.From Frompeering peeringinto intothe thebrains brainsofofdreamdreaming ingindividuals, individuals,and andprecisely preciselyhow howdreams dreamsinspire inspireNobel NobelPrize–winPrize–winning ningideas ideasthat thattransform transformthe theworld, world,totowhether whetherorornot notdream dreamcontrol control really reallyisispossible, possible,and andififsuch suchaathing thingisiseven evenwise—all wise—allwill willbe berevealed. revealed.

Part Part44seats seatsus usfirst firstatatthe thebedside, bedside,explaining explainingnumerous numeroussleep sleepdisordisorders, ders,including includinginsomnia. insomnia.I Iwill willunpack unpackthe theobvious obviousand andnot-sonot-so-obvious obvious reasons reasonsfor forwhy whyso somany manyofofus usfind findititdifficult difficulttotoget getaagood goodnight’s night’s sleep, sleep,night nightafter afternight. night.AAdiscussion discussionofofsleeping sleepingpills pillsthen thenfollows, follows,

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based basedon onscientific scientificand andclinical clinicaldata. data.Details Detailsofofnew, new,safer, safer,and andmore more effective effectivenon-drug non-drugtherapies therapiesfor forbetter bettersleep sleepwill willthen thenbe bedescribed. described.

Transitioning Transitioningfrom frombedside bedsideup uptotothe thelevel levelofofsleep sleepininsociety, society,we wewill will subsequently subsequentlylearn learnofofthe thesobering soberingimpact impactthat thatinsufficient insufficientsleep sleephas has inineducation, education,ininmedicine medicineand andhealth healthcare, care,and andininbusiness. business.The Theevievidence denceshatters shattersbeliefs beliefsabout aboutthe theusefulness usefulnessofoflong longwaking wakinghours hourswith with little littlesleep sleepinineffectively, effectively,safely, safely,profitably, profitably,and andethically ethicallyaccomplishing accomplishing the thegoals goalsofofeach eachofofthese thesedisciplines. disciplines.Concluding Concludingthe thebook bookwith withgenugenuine ineoptimistic optimistichope, hope,I Ilay layout outaaroad roadmap mapofofideas ideasthat thatcan canreconnect reconnect humanity humanitywith withthe thesleep sleepititremains remainsso sobereft bereftof—a of—anew newvision visionfor forsleep sleep ininthe thetwenty-first twenty-firstcentury. century.

I Ishould shouldnote notethat thatyou youneed neednot notread readthis thisbook bookininthis thisprogressive, progressive, four-part four-partnarrative narrativearc. arc.Each Eachchapter chaptercan, can,for forthe themost mostpart, part,be beread read individually, individually,and andout outofoforder, order,without withoutlosing losingtoo toomuch muchofofits itssignifisignificance. cance.I Itherefore thereforeinvite inviteyou youtotoconsume consumethe thebook bookininwhole wholeororininpart, part, buffet-style buffet-styleororininorder, order,all allaccording accordingtotoyour yourpersonal personaltaste. taste.

ItItisisworthwhile worthwhilepointing pointingout outthat thatthis thisbook bookisisnot notdesigned designedtotobe be aaself-help self-helpguide. guide.ItItisisnot notwritten writtentototarget targetorortreat treatsleep sleepdisorders, disorders, including includinginsomnia. insomnia.There Thereare arebooks booksthat thatdo dothis, this,and andmany manyofofthem them will willrecommend recommendspeaking speakingtotoaadoctor doctorififyou yoususpect suspectyou youhave haveaasleep sleep disorder. disorder.I Iam amalso alsovery veryunderstanding understandingof, of,and andsympathetic sympatheticto, to,those those people peoplewho whostruggle strugglewith withsleep sleepand andare aremost mostanxious anxiousabout aboutit.it.For For these theseindividuals, individuals,ititisispossible possiblethat thattheir theiranxiety anxietymay mayincrease increasewhen when reading readingabout aboutthe theimpact impactofofinsufficient insufficientsleep, sleep,including includinginformation information contained containedininthe thebook. book.I Itherefore thereforewant wanttotoalert alertthe thereader readertotothis this possibility, possibility,allowing allowingfor forreader readerdiscretion discretionon onthis thismatter. matter.

InInclosing, closing,I Ioffer offeraadisclaimer. disclaimer.Should Shouldyou youfeel feeldrowsy drowsyand andfall fallasleep asleep while whilereading readingthe thebook, book,unlike unlikemost mostauthors, authors,I Iwill willnot notbe bedisheartened. disheartened.

Indeed, Indeed,based basedon onthe thetopic topicand andcontent contentofofthis thisbook, book,I Iam amactively activelygoing going totoencourage encouragethat thatkind kindofofbehavior behaviorfrom fromyou. you.Knowing Knowingwhat whatI Iknow know about aboutthe therelationship relationshipbetween betweensleep sleepand andmemory, memory,ititisisthe thegreatest greatest form formofofflattery flatteryfor forme metotoknow knowthat thatyou, you,the thereader, reader,cannot cannotresist resistthe the urge urgetotostrengthen strengthenand andthus thusremember rememberwhat whatI Iam amtelling tellingyou youby byfalling falling asleep. asleep.So Soplease, please,feel feelfree freetotoebb ebband andflow flowinto intoand andout outofofconsciousness consciousness during duringthis thisentire entirebook. book.I Iwill willtake takeabsolutely absolutelyno nooffense. offense.On Onthe theconcontrary, trary,I Iwould wouldbe bedelighted. delighted.

CHAPTER CHAPTER22

Caffeine, Caffeine,Jet JetLag, Lag,and andMelatonin Melatonin Losing Losingand andGaining GainingControl ControlofofYour YourSleep SleepRhythm Rhythm

How Howdoes doesyour yourbody bodyknow knowwhen whenit’s it’stime timetotosleep? sleep?Why Whydo doyou yousuffer suffer from fromjet jetlag lagafter afterarriving arrivingininaanew newtime timezone? zone?How Howdo doyou youovercome overcome jet jetlag? lag?Why Whydoes doesthat thatacclimatization acclimatizationcause causeyou youyet yetmore morejet jetlag lagupon upon returning returninghome? home?Why Whydo dosome somepeople peopleuse usemelatonin melatonintotocombat combatthese these issues? issues?Why Why(and (andhow) how)does doesaacup cupofofcoffee coffeekeep keepyou youawake? awake?Perhaps Perhaps most mostimportantly, importantly,how howdo doyou youknow knowififyou’re you’regetting gettingenough enoughsleep? sleep?

There Thereare aretwo twomain mainfactors factorsthat thatdetermine determinewhen whenyou youwant wanttotosleep sleep and andwhen whenyou youwant wanttotobe beawake. awake.As Asyou youread readthese thesevery verywords, words,both both factors factorsare arepowerfully powerfullyinfluencing influencingyour yourmind mindand andbody. body.The Thefirst firstfacfactor torisisaasignal signalbeamed beamedout outfrom fromyour yourinternal internaltwenty-four-hour twenty-four-hourclock clock located locateddeep deepwithin withinyour yourbrain. brain.The Theclock clockcreates createsaacycling, cycling,day-night day-night rhythm rhythmthat thatmakes makesyou youfeel feeltired tiredororalert alertatatregular regulartimes timesofofnight nightand and day, day,respectively. respectively.The Thesecond secondfactor factorisisaachemical chemicalsubstance substancethat thatbuilds builds up upininyour yourbrain brainand andcreates createsaa“sleep “sleeppressure. pressure. ” ”The Thelonger longeryou’ve you’vebeen been awake, awake,the themore morethat thatchemical chemicalsleep sleeppressure pressureaccumulates, accumulates,and andconseconsequentially, quentially,the thesleepier sleepieryou youfeel. feel.ItItisisthe thebalance balancebetween betweenthese thesetwo twofacfactors torsthat thatdictates dictateshow howalert alertand andattentive attentiveyou youare areduring duringthe theday, day,when when you youwill willfeel feeltired tiredand andready readyfor forbed bedatatnight, night,and, and,ininpart, part,how howwell wellyou you will willsleep. sleep.

GOT GOT RHYTHM? RHYTHM? Central Centraltotomany manyofofthe thequestions questionsininthe theopening openingparagraph paragraphisisthe thepowpowerful erfulsculpting sculptingforce forceofofyour yourtwenty-four-hour twenty-four-hourrhythm, rhythm,also alsoknown knownasas your yourcircadian circadianrhythm. rhythm.Everyone Everyonegenerates generatesaacircadian circadianrhythm rhythm(circa, (circa,

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meaning meaning “around, “around,” ” and and dian, dian, derivative derivative ofof diam, diam, meaning meaning “day”). “day”).

Indeed, Indeed,most mostliving livingcreatures creatureson onthe theplanet planetwith withaalife lifespan spanofofmore more than thanseveral severaldays daysgenerates generatesthis thisnatural naturalcycle. cycle.The Theinternal internaltwentytwentyfour-hour four-hourclock clockwithin withinyour yourbrain braincommunicates communicatesits itsdaily dailycircadian circadian rhythm rhythmsignal signaltotoevery everyother otherregion regionofofyour yourbrain brainand andevery everyorgan organinin your yourbody. body.

Your Yourtwenty-four-hour twenty-four-hourtempo tempohelps helpstotodetermine determinewhen whenyou youwant want totobe beawake awakeand andwhen whenyou youwant wanttotobe beasleep. asleep.But Butititcontrols controlsother other rhythmic rhythmicpatterns, patterns,too. too.These Theseinclude includeyour yourtimed timedpreferences preferencesfor foreateating ingand anddrinking, drinking,your yourmoods moodsand andemotions, emotions,the theamount amountofofurine urineyou you produce,* produce,*your yourcore corebody bodytemperature, temperature,your yourmetabolic metabolicrate, rate,and andthe the release releaseofofnumerous numeroushormones. hormones.ItItisisno nocoincidence coincidencethat thatthe thelikelihood likelihood ofofbreaking breakingan anOlympic Olympicrecord recordhas hasbeen beenclearly clearlytied tiedtototime timeofofday, day,being being maximal maximalatatthe thenatural naturalpeak peakofofthe thehuman humancircadian circadianrhythm rhythmininthe theearly early afternoon. afternoon.Even Eventhe thetiming timingofofbirths birthsand anddeaths deathsdemonstrates demonstratescircadian circadian rhythmicity rhythmicitydue duetotothe themarked markedswings swingsininkey keylife-dependent life-dependentmetabolic, metabolic, cardiovascular, cardiovascular,temperature, temperature,and andhormonal hormonalprocesses processesthat thatthis thispacepacemaker makercontrols. controls.

Long Longbefore beforewe wediscovered discoveredthis thisbiological biologicalpacemaker, pacemaker,an aningenious ingenious experiment experimentdid didsomething somethingutterly utterlyremarkable: remarkable:stopped stoppedtime—at time—atleast, least, for for aa plant. plant. ItIt was was inin 1729 1729 when when French French geophysicist geophysicist Jean-Jacques Jean-Jacques d’Ortous d’Ortousde deMairan Mairandiscovered discoveredthe thevery veryfirst firstevidence evidencethat thatplants plantsgengenerate eratetheir theirown owninternal internaltime. time.

De DeMairan Mairanwas wasstudying studyingthe theleaf leafmovements movementsofofaaspecies speciesthat thatdisdisplayed playedheliotropism: heliotropism:when whenaaplant’s plant’sleaves leavesororflowers flowerstrack trackthe thetrajectrajectory toryofofthe thesun sunasasititmoves movesacross acrossthe thesky skyduring duringthe theday. day.De DeMairan Mairanwas was Notonly only intrigued intriguedby byone oneplant plantininparticular, particular,called calledMimosa Mimosapudica. pudica.† †Not do dothe theleaves leavesofofthis thisplant planttrace tracethe thearching archingdaytime daytimepassage passageofofthe thesun sun across acrossthe thesky’s sky’sface, face,but butatatnight, night,they theycollapse collapsedown, down,almost almostasasthough though they theyhad hadwilted. wilted.Then, Then,atatthe thestart startofofthe thefollowing followingday, day,the theleaves leavespop pop *I*Ishould shouldnote, note,from frompersonal personalexperience, experience,that thatthis thisisisaawinning winningfact facttotodispense dispenseatatdinner dinner parties, parties,family familygatherings, gatherings,ororother othersuch suchsocial socialoccasions. occasions.ItItwill willalmost almostguarantee guaranteenobody nobody will willapproach approachororspeak speaktotoyou youagain againfor forthe therest restofofthe theevening, evening,and andyou’ll you’llalso alsonever neverbebe invited invitedback. back. †† The Theword wordpudica pudicaisisfrom fromthe theLatin Latinmeaning meaning“shy” “shy”oror“bashful, “bashful, ” ”since sincethe theleaves leaveswill willalso also collapse collapsedown downififyou youtouch touchororstroke strokethem. them.

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open openonce onceagain againlike likean anumbrella, umbrella,healthy healthyasasever. ever.This Thisbehavior behaviorrepeats repeats each eachand andevery everymorning morningand andevening, evening,and andititcaused causedthe thefamous famousevoluevolutionary tionarybiologist biologistCharles CharlesDarwin Darwintotocall callthem them“sleeping “sleepingleaves. leaves. ”” Prior Priortotode deMairan’s Mairan’sexperiment, experiment,many manybelieved believedthat thatthe theexpanding expanding and andretracting retractingbehavior behaviorofofthe theplant plantwas wassolely solelydetermined determinedby bythe thecorcorresponding respondingrising risingand andsetting settingofofthe thesun. sun.ItItwas wasaalogical logicalassumption: assumption: daylight daylight(even (evenon oncloudy cloudydays) days)triggered triggeredthe theleaves leavestotoopen openwide, wide,while while ensuing ensuingdarkness darknessinstructed instructedthe theleaves leavestotoshut shutup upshop, shop,close closefor forbusibusiness, ness,and andfold foldaway. away.That Thatassumption assumptionwas wasshattered shatteredby byde deMairan.

Mairan.First, First, he hetook tookthe theplant plantand andplaced placedititout outininthe theopen, open,exposing exposingitittotothe thesignals signals ofoflight lightand anddark darkassociated associatedwith withday dayand andnight. night.As Asexpected, expected,the theleaves leaves expanded expandedduring duringthe thelight lightofofday dayand andretracted retractedwith withthe thedark darkofofnight. night.

Then Thencame camethe thegenius geniustwist. twist.De DeMairan Mairanplaced placedthe theplant plantininaasealed sealed box boxfor forthe thenext nexttwenty-four-hour twenty-four-hourperiod, period,plunging plungingititinto intototal totaldark dark for forboth bothday dayand andnight. night.During Duringthese thesetwenty-four twenty-fourhours hoursofofblackness, blackness, he hewould wouldoccasionally occasionallytake takeaapeek peekatatthe theplant plantinincontrolled controlleddarkness, darkness, observing observingthe thestate stateofofthe theleaves. leaves.Despite Despitebeing beingcut cutoff offfrom fromthe theinfluinfluence enceofoflight lightduring duringthe theday, day,the theplant plantstill stillbehaved behavedasasthough thoughititwere were being beingbathed bathedininsunlight; sunlight;its itsleaves leaveswere wereproudly proudlyexpanded. expanded.Then, Then,itit retracted retractedits itsleaves leavesasasififon oncue cueatatthe theend endofofthe theday, day,even evenwithout withoutthe the sun’s sun’ssetting settingsignal, signal,and andthey theystayed stayedcollapsed collapsedthroughout throughoutthe theentire entire night. night.

ItItwas wasaarevolutionary revolutionarydiscovery: discovery:de deMairan Mairanhad hadshown shownthat thataalivliving ingorganism organismkept keptits itsown owntime, time,and andwas wasnot, not,ininfact, fact,slave slavetotothe thesun’s sun’s rhythmic rhythmiccommands. commands.Somewhere Somewherewithin withinthe theplant plantwas wasaatwenty-fourtwenty-fourhour hourrhythm rhythmgenerator generatorthat thatcould couldtrack tracktime timewithout withoutany anycues cuesfrom fromthe the outside outsideworld, world,such suchasasdaylight. daylight.The Theplant plantdidn’t didn’tjust justhave haveaacircadian circadian rhythm, rhythm,itithad hadan an“endogenous, “endogenous, ” ”ororself-generated, self-generated,rhythm. rhythm.ItItisismuch much like likeyour yourheart heartdrumming drummingout outits itsown ownself-generating self-generatingbeat. beat.The Thedifferdifference enceisissimply simplythat thatyour yourheart’s heart’spacemaker pacemakerrhythm rhythmisisfar farfaster, faster,usually usually beating beatingatatleast leastonce onceaasecond, second,rather ratherthan thanonce onceevery everytwenty-four-hour twenty-four-hour period periodlike likethe thecircadian circadianclock. clock.

Surprisingly, Surprisingly,itittook tookanother anothertwo twohundred hundredyears yearstotoprove provethat thatwe we humans humanshave haveaasimilar, similar,internally internallygenerated generatedcircadian circadianrhythm. rhythm.But Butthis this experiment experimentadded addedsomething somethingrather ratherunexpected unexpectedtotoour ourunderstanding understanding ofofinternal internaltimekeeping. timekeeping.ItItwas was1938, 1938,and andProfessor ProfessorNathaniel NathanielKleitman Kleitman

WHY WHY WE WE SLEEP SLEEP

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atatthe theUniversity UniversityofofChicago, Chicago,accompanied accompaniedby byhis hisresearch researchassistant assistant Bruce Bruce Richardson, Richardson, were were toto perform perform an an even even more more radical radical scientific scientific study. study.ItItrequired requiredaatype typeofofdedication dedicationthat thatisisarguably arguablywithout withoutmatch matchoror comparison comparisontotothis thisday. day.

Kleitman Kleitmanand andRichardson Richardsonwere weretotobe betheir theirown ownexperimental experimentalguinea guinea pigs. pigs.Loaded Loadedwith withfood foodand andwater waterfor forsix sixweeks weeksand andaapair pairofofdismantled, dismantled, high-standing high-standinghospital hospitalbeds, beds,they theytook tookaatrip tripinto intoMammoth MammothCave Caveinin Kentucky, Kentucky,one oneofofthe thedeepest deepestcaverns cavernson onthe theplanet—so planet—sodeep, deep,ininfact, fact, that thatno nodetectable detectablesunlight sunlightpenetrates penetratesits itsfarthest farthestreaches. reaches.ItItwas wasfrom from this thisdarkness darknessthat thatKleitman Kleitmanand andRichardson Richardsonwere weretotoilluminate illuminateaastrikstriking ingscientific scientificfinding findingthat thatwould woulddefine defineour ourbiological biologicalrhythm rhythmasasbeing being approximately approximatelyone oneday day(circadian), (circadian),and andnot notprecisely preciselyone oneday. day.

InInaddition additiontotofood foodand andwater, water,the thetwo twomen menbrought broughtaahost hostofofmeameasuring suringdevices devicestotoassess assesstheir theirbody bodytemperatures, temperatures,asaswell wellasastheir theirwakwaking ingand andsleeping sleepingrhythms. rhythms.This Thisrecording recordingarea areaformed formedthe theheart heartofoftheir their living livingspace, space,flanked flankedeither eitherside sideby bytheir theirbeds. beds.The Thetall tallbed bedlegs legswere were each eachseated seatedininaabucket bucketofofwater, water,castle-moat castle-moatstyle, style,totodiscourage discouragethe the innumerable innumerablesmall small(and (andnot notso sosmall) small)creatures creatureslurking lurkingininthe thedepths depthsofof Mammoth MammothCave Cavefrom fromjoining joiningthem themininbed. bed.

The Theexperimental experimentalquestion questionfacing facingKleitman Kleitmanand andRichardson Richardsonwas was simple: simple:When Whencut cutoff offfrom fromthe thedaily dailycycle cycleofoflight lightand anddark, dark,would wouldtheir their biological biologicalrhythms rhythmsofofsleep sleepand andwakefulness, wakefulness,together togetherwith withbody bodytemtemperature, perature,become becomecompletely completelyerratic, erratic,ororwould wouldthey theystay staythe thesame sameasas those thoseindividuals individualsininthe theoutside outsideworld worldexposed exposedtotorhythmic rhythmicdaylight? daylight?

InIntotal, total,they theylasted lastedthirty-two thirty-twodays daysinincomplete completedarkness. darkness.Not Notonly onlydid did they theyaggregate aggregatesome someimpressive impressivefacial facialhair, hair,but butthey theymade madetwo twogroundgroundbreaking breakingdiscoveries discoveriesininthe theprocess. process.The Thefirst firstwas wasthat thathumans, humans,like likede de Mairan’s Mairan’sheliotrope heliotropeplants, plants,generated generatedtheir theirown ownendogenous endogenouscircadian circadian rhythm rhythmininthe theabsence absenceofofexternal externallight lightfrom fromthe thesun. sun.That Thatis,is,neither neither Kleitman Kleitmannor norRichardson Richardsondescended descendedinto intorandom randomspurts spurtsofofwake wakeand and sleep, sleep, but but instead instead expressed expressed aa predictable predictable and and repeating repeating pattern pattern ofof prolonged prolongedwakefulness wakefulness(about (aboutfifteen fifteenhours), hours),paired pairedwith withconsolidated consolidated bouts boutsofofabout aboutnine ninehours hoursofofsleep. sleep.

The Thesecond secondunexpected—and unexpected—andmore moreprofound—result profound—resultwas wasthat thattheir their reliably reliablyrepeating repeatingcycles cyclesofofwake wakeand andsleep sleepwere werenot notprecisely preciselytwentytwentyfour four hours hours inin length, length, but but consistently consistently and and undeniably undeniably longer longer than than

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MATTHEW MATTHEW WALKER WALKER

twenty-four twenty-fourhours. hours.Richardson, Richardson,ininhis histwenties, twenties,developed developedaasleep-wake sleep-wake cycle cycleofofbetween betweentwenty-six twenty-sixand andtwenty-eight twenty-eighthours hoursininlength. length.That That ofofKleitman, Kleitman,ininhis hisforties, forties,was wasaalittle littlecloser closerto, to,but butstill stilllonger longerthan, than, twenty-four twenty-fourhours. hours.Therefore, Therefore,when whenremoved removedfrom fromthe theexternal externalinfluinfluence enceofofdaylight, daylight,the theinternally internallygenerated generated“day” “day”ofofeach eachman manwas wasnot not exactly exactlytwenty-four twenty-fourhours, hours,but butaalittle littlemore morethan thanthat. that.Like Likean aninaccuinaccurate ratewristwatch wristwatchwhose whosetime timeruns runslong, long,with witheach eachpassing passing(real) (real)day dayinin the theoutside outsideworld, world,Kleitman Kleitmanand andRichardson Richardsonbegan begantotoadd addtime timebased based on ontheir theirlonger, longer,internally internallygenerated generatedchronometry. chronometry.

Since Since our our innate innate biological biological rhythm rhythm isis not not precisely precisely twenty-four twenty-four hours, hours,but butthereabouts, thereabouts,aanew newnomenclature nomenclaturewas wasrequired: required:the thecircadian circadian rhythm—that rhythm—thatis,is,one onethat thatisisapproximately, approximately,ororaround, around,one oneday dayininlength, length, and andnot notprecisely preciselyone oneday.* day.*InInthe theseventy-plus seventy-plusyears yearssince sinceKleitman Kleitman and andRichardson’s Richardson’sseminal seminalexperiment, experiment,we wehave havenow nowdetermined determinedthat that the theaverage averageduration durationofofaahuman humanadult’s adult’sendogenous endogenouscircadian circadianclock clock runs runsaround aroundtwenty-four twenty-fourhours hoursand andfifteen fifteenminutes minutesininlength. length.Not Nottoo too far faroff offthe thetwenty-four-hour twenty-four-hourrotation rotationofofthe theEarth, Earth,but butnot notthe theprecise precise timing timingthat thatany anyself-respecting self-respectingSwiss Swisswatchmaker watchmakerwould wouldever everaccept. accept.

Thankfully, Thankfully,most mostofofus usdon’t don’tlive liveininMammoth MammothCave, Cave,ororthe theconstant constant darkness darknessititimposes. imposes.We Weroutinely routinelyexperience experiencelight lightfrom fromthe thesun sunthat that comes comestotothe therescue rescueofofour ourimprecise, imprecise,overrunning overrunninginternal internalcircadian circadian clock. clock.Sunlight Sunlightacts actslike likeaamanipulating manipulatingfinger fingerand andthumb thumbon onthe thesidesidedial dialofofan animprecise imprecisewristwatch. wristwatch.The Thelight lightofofthe thesun sunmethodically methodicallyresets resets our ourinaccurate inaccurateinternal internaltimepiece timepieceeach eachand andevery everyday, day,“winding” “winding”us us back backtotoprecisely, precisely,not notapproximately, approximately,twenty-four twenty-fourhours. hours.† † ItItisisno nocoincidence coincidencethat thatthe thebrain brainuses usesdaylight daylightfor forthis thisresetting resetting purpose. purpose.Daylight Daylightisisthe themost mostreliable, reliable,repeating repeatingsignal signalthat thatwe wehave have ininour ourenvironment. environment.Since Sincethe thebirth birthofofour ourplanet, planet,and andevery everysingle single day daythereafter thereafterwithout withoutfail, fail,the thesun sunhas hasalways alwaysrisen risenininthe themorning morning and andset setininthe theevening. evening.Indeed, Indeed,the thereason reasonmost mostliving livingspecies specieslikely likely *This *Thisphenomenon phenomenonofofan animprecise impreciseinternal internalbiological biologicalclock clockhas hasnow nowbeen beenconsistently consistently observed observedininmany manydifferent differentspecies. species.However, However,ititisisnot notconsistently consistentlylong longininallallspecies, species,asas ititisisininhumans. humans.For Forsome, some,the theendogenous endogenouscircadian circadianrhythm rhythmruns runsshort, short,being beingless lessthan than twenty-four twenty-fourhours hourswhen whenplaced placedinintotal totaldarkness, darkness,such suchasashamsters hamstersororsquirrels. squirrels.For Forothers, others, such suchasashumans, humans,ititisislonger longerthan thantwenty-four twenty-fourhours. hours. †† Even Evensunlight sunlightcoming comingthrough throughthick thickcloud cloudon onaarainy rainyday dayisispowerful powerfulenough enoughtotohelp helpreset reset our ourbiological biologicalclocks. clocks.

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adopted adoptedaacircadian circadianrhythm rhythmisistotosynchronize synchronizethemselves themselvesand andtheir their activities, activities,both bothinternal internal(e.g., (e.g.,temperature) temperature)and andexternal external(e.g., (e.g.,feedfeeding), ing),with withthe thedaily dailyorbital orbitalmechanics mechanicsofofplanet planetEarth Earthspinning spinningon onits its axis, axis,resulting resultingininregular regularphases phasesofoflight light(sun (sunfacing) facing)and anddark dark(sun (sun hiding). hiding).

Yet Yetdaylight daylightisn’t isn’tthe theonly onlysignal signalthat thatthe thebrain braincan canlatch latchon ontotofor for the thepurpose purposeofofbiological biologicalclock clockresetting, resetting,though thoughititisisthe theprincipal principal and andpreferential preferentialsignal, signal,when whenpresent. present.So Solong longasasthey theyare arereliably reliably repeating, repeating,the thebrain braincan canalso alsouse useother otherexternal externalcues, cues,such suchasasfood, food, exercise, exercise,temperature temperaturefluctuations, fluctuations,and andeven evenregularly regularlytimed timedsocial social interaction. interaction.All Allofofthese theseevents eventshave havethe theability abilitytotoreset resetthe thebiologibiological calclock, clock,allowing allowingitittotostrike strikeaaprecise precisetwenty-four-hour twenty-four-hournote. note.ItItisis the thereason reasonthat thatindividuals individualswith withcertain certainforms formsofofblindness blindnessdo donot not entirely entirelylose losetheir theircircadian circadianrhythm. rhythm.Despite Despitenot notreceiving receivinglight lightcues cues due duetototheir theirblindness, blindness,other otherphenomena phenomenaact actasastheir theirresetting resettingtrigtriggers. gers.Any Anysignal signalthat thatthe thebrain brainuses usesfor forthe thepurpose purposeofofclock clockresetting resetting isistermed termedaazeitgeber, zeitgeber,from fromthe theGerman German“time “timegiver” giver”oror“synchronizer. “synchronizer.” ” Thus, Thus,while whilelight lightisisthe themost mostreliable reliableand andthus thusthe theprimary primaryzeitgezeitgeber, ber,there thereare aremany manyfactors factorsthat thatcan canbe beused usedininaddition additionto, to,ororininthe the absence absenceof, of,daylight. daylight.

The Thetwenty-four-hour twenty-four-hourbiological biologicalclock clocksitting sittingininthe themiddle middleofofyour your brain brainisiscalled calledthe thesuprachiasmatic suprachiasmatic(pronounced (pronouncedsoo-pra-kai-as-MATsoo-pra-kai-as-MATik) ik)nucleus. nucleus.As Aswith withmuch muchofofanatomical anatomicallanguage, language,the thename, name,while while far farfrom fromeasy easytotopronounce, pronounce,isisinstructional: instructional:supra, supra,meaning meaningabove, above, and andchiasm, chiasm,meaning meaningaacrossing crossingpoint. point.The Thecrossing crossingpoint pointisisthat thatofof the theoptic opticnerves nervescoming comingfrom fromyour youreyeballs. eyeballs.Those Thosenerves nervesmeet meetininthe the middle middleofofyour yourbrain, brain,and andthen theneffectively effectivelyswitch switchsides. sides.The Thesuprachiassuprachiasmatic maticnucleus nucleusisislocated locatedjust justabove abovethis thisintersection intersectionfor foraagood goodreason. reason.

ItIt“samples” “samples”the thelight lightsignal signalbeing beingsent sentfrom fromeach eacheye eyealong alongthe theoptic optic nerves nervesasasthey theyhead headtoward towardthe theback backofofthe thebrain brainfor forvisual visualprocessprocessing. ing.The Thesuprachiasmatic suprachiasmaticnucleus nucleususes usesthis thisreliable reliablelight lightinformation information totoreset resetits itsinherent inherenttime timeinaccuracy inaccuracytotoaacrisp crisptwenty-four-hour twenty-four-hourcycle, cycle, preventing preventingany anydrift. drift.

When WhenI Itell tellyou youthat thatthe thesuprachiasmatic suprachiasmaticnucleus nucleusisiscomposed composedofof 20,000 20,000brain braincells, cells,ororneurons, neurons,you youmight mightassume assumeititisisenormous, enormous,conconsuming sumingaavast vastamount amountofofyour yourcranial cranialspace, space,but butactually actuallyititisistiny. tiny.The The

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brain brainisiscomposed composedofofapproximately approximately100 100billion billionneurons, neurons,making makingthe the suprachiasmatic suprachiasmaticnucleus nucleusminuscule minusculeininthe therelative relativescheme schemeofofcerebral cerebral matter. matter.Yet Yetdespite despiteits itsstature, stature,the theinfluence influenceofofthe thesuprachiasmatic suprachiasmatic nucleus nucleuson onthe therest restofofthe thebrain brainand andthe thebody bodyisisanything anythingbut butmeek. meek.

This Thistiny tinyclock clockisisthe thecentral centralconductor conductorofoflife’s life’sbiological biologicalrhythmic rhythmic symphony—yours symphony—yoursand andevery everyother otherliving livingspecies. species.The Thesuprachiasmatic suprachiasmatic nucleus nucleuscontrols controlsaavast vastarray arrayofofbehaviors, behaviors,including includingour ourfocus focusininthis this chapter: chapter:when whenyou youwant wanttotobe beawake awakeand andasleep. asleep.

For Fordiurnal diurnalspecies speciesthat thatare areactive activeduring duringthe theday, day,such suchasashumans, humans, the thecircadian circadianrhythm rhythmactivates activatesmany manybrain brainand andbody bodymechanisms mechanismsinin the thebrain brainand andbody bodyduring duringdaylight daylighthours hoursthat thatare aredesigned designedtotokeep keepyou you awake awakeand andalert. alert.These Theseprocesses processesare arethen thenratcheted ratcheteddown downatatnighttime, nighttime, removing removingthat thatalerting alertinginfluence. influence.Figure Figure11shows showsone onesuch suchexample exampleofof aacircadian circadianrhythm—that rhythm—thatofofyour yourbody bodytemperature. temperature.ItItrepresents representsaveraverage agecore corebody bodytemperature temperature(rectal, (rectal,no noless) less)ofofaagroup groupofofhuman humanadults. adults.

Starting Startingatat“12 “12pm” pm”on onthe thefar farleft, left,body bodytemperature temperaturebegins beginstotorise, rise,peakpeaking inglate lateininthe theafternoon. afternoon.The Thetrajectory trajectorythen thenchanges. changes.Temperature Temperature begins beginstotodecline declineagain, again,dropping droppingbelow belowthat thatofofthe themidday middaystart-point start-point WhyWeSleep_TO_1_circadian.pdf WhyWeSleep_TO_1_circadian.pdf 1 1 5/11/17 5/11/17 10:27 10:27AM AM asasbedtime bedtimeapproaches. approaches.

Figure Figure1:1:Typical TypicalTwenty-Four-Hour Twenty-Four-HourCircadian CircadianRhythm Rhythm (Core (CoreBody BodyTemperature) Temperature) Rectal Temperature (°C) Rectal Temperature (°C)

37.2 37.2 37.1 37.1 37.0 37.0 36.9 36.9 36.8 36.8 36.7 36.7 36.6 36.6 1212pm pm 44pm pm 88pm pm 1212am am 44am am 88am am Time Time(Twenty-Four (Twenty-FourHours) Hours)

Your Yourbiological biologicalcircadian circadianrhythm rhythmcoordinates coordinatesaadrop dropinincore corebody body temperature temperature asas you you near near typical typical bedtime bedtime (figure (figure 1), 1), reaching reaching its its nadir, nadir,ororlow lowpoint, point,about abouttwo twohours hoursafter aftersleep sleeponset. onset.However, However,this this temperature temperaturerhythm rhythmisisnot notdependent dependentupon uponwhether whetheryou youare areactually actually

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asleep. asleep.IfIfI Iwere weretotokeep keepyou youawake awakeall allnight, night,your yourcore corebody bodytemperatemperature turewould wouldstill stillshow showthe thesame samepattern. pattern.Although Althoughthe thetemperature temperature drop drophelps helpstotoinitiate initiatesleep, sleep,the thetemperature temperaturechange changeitself itselfwill willrise rise and andfall fallacross acrossthe thetwenty-four-hour twenty-four-hourperiod periodregardless regardlessofofwhether whether you youare areawake awakeororasleep. asleep.ItItisisaaclassic classicdemonstration demonstrationofofaaprepropreprogrammed grammedcircadian circadianrhythm rhythmthat thatwill willrepeat repeatover overand andover overwithout without fail, fail,like likeaametronome. metronome.Temperature Temperatureisisjust justone oneofofmany manytwenty-fourtwenty-fourhour hourrhythms rhythmsthat thatthe thesuprachiasmatic suprachiasmaticnucleus nucleusgoverns. governs.WakefulWakefulness ness and and sleep sleep are are another. another. Wakefulness Wakefulness and and sleep sleep are are therefore therefore under underthe thecontrol controlofofthe thecircadian circadianrhythm, rhythm,and andnot notthe theother otherway way around. around. That That is,is, your your circadian circadian rhythm rhythm will will march march up up and and down down every everytwenty-four twenty-fourhours hoursirrespective irrespectiveofofwhether whetheryou youhave haveslept sleptoror not. not.Your Yourcircadian circadianrhythm rhythmisisunwavering unwaveringininthis thisregard. regard.But Butlook look across acrossindividuals, individuals,and andyou youdiscover discoverthat thatnot noteveryone’s everyone’scircadian circadian timing timingisisthe thesame. same.

MY MY RHYTHM RHYTHM IS IS NOT NOT YOUR YOUR RHYTHM RHYTHM Although Althoughhuman humanbeings beingsdisplay displayan anunyielding unyieldingtwenty-four-hour twenty-four-hourpatpattern, tern,the therespective respectivepeak peakand andtrough troughpoints pointsare arestrikingly strikinglydifferent differentfrom from one oneindividual individualtotothe thenext. next.For Forsome somepeople, people,their theirpeak peakofofwakefulness wakefulness arrives arrivesearly earlyininthe theday, day,and andtheir theirsleepiness sleepinesstrough trougharrives arrivesearly earlyatatnight. night.

These Theseare are“morning “morningtypes, types, ” ”and andmake makeup upabout about40 40percent percentofofthe thepopupopulace. lace.They Theyprefer prefertotowake wakeatatororaround arounddawn, dawn,are arehappy happytotodo doso, so,and and function functionoptimally optimallyatatthis thistime timeofofday. day.Others Othersare are“evening “eveningtypes, types, ” ”and and account accountfor forapproximately approximately30 30percent percentofofthe thepopulation. population.They Theynaturally naturally prefer prefergoing goingtotobed bedlate lateand andsubsequently subsequentlywake wakeup uplate latethe thefollowing following morning, morning,ororeven evenininthe theafternoon. afternoon.The Theremaining remaining30 30percent percentofofpeople people lie liesomewhere somewhereininbetween betweenmorning morningand andevening eveningtypes, types,with withaaslight slight leaning leaningtoward towardeveningness, eveningness,like likemyself. myself.

You Youmay maycolloquially colloquiallyknow knowthese thesetwo twotypes typesofofpeople peopleasas“morning “morning larks” larks”and and“night “nightowls, owls,” ”respectively. respectively.Unlike Unlikemorning morninglarks, larks,night nightowls owls are arefrequently frequentlyincapable incapableofoffalling fallingasleep asleepearly earlyatatnight, night,no nomatter matterhow how hard hardthey theytry. try.ItItisisonly onlyininthe theearly-morning early-morninghours hoursthat thatowls owlscan candrift drift off. off.Having Havingnot notfallen fallenasleep asleepuntil untillate, late,owls owlsofofcourse coursestrongly stronglydislike dislike waking wakingup upearly. early.They Theyare areunable unabletotofunction functionwell wellatatthis thistime, time,one one

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cause causeofofwhich whichisisthat, that,despite despitebeing being“awake, “awake,” ”their theirbrain brainremains remainsininaa more moresleep-like sleep-likestate statethroughout throughoutthe theearly earlymorning. morning.This Thisisisespecially especially true trueofofaaregion regioncalled calledthe theprefrontal prefrontalcortex, cortex,which whichsits sitsabove abovethe theeyes, eyes, and andcan canbe bethought thoughtofofasasthe thehead headoffice officeofofthe thebrain. brain.The Theprefrontal prefrontal cortex cortexcontrols controlshigh-level high-levelthought thoughtand andlogical logicalreasoning, reasoning,and andhelps helps keep keepour ouremotions emotionsinincheck. check.When Whenaanight nightowl owlisisforced forcedtotowake wakeup up too tooearly, early,their theirprefrontal prefrontalcortex cortexremains remainsininaadisabled, disabled,“offline” “offline”state. state.

Like Likeaacold coldengine engineafter afteran anearly-morning early-morningstart, start,itittakes takesaalong longtime time before beforeititwarms warmsup uptotooperating operatingtemperature, temperature,and andbefore beforethat thatwill willnot not function functionefficiently. efficiently.

An Anadult’s adult’sowlness owlnessororlarkness, larkness,also alsoknown knownasastheir theirchronotype, chronotype, isisstrongly stronglydetermined determinedby bygenetics. genetics.IfIfyou youare areaanight nightowl, owl,it’s it’slikely likely that thatone one(or (orboth) both)ofofyour yourparents parentsisisaanight nightowl. owl.Sadly, Sadly,society societytreats treats night nightowls owlsrather ratherunfairly unfairlyon ontwo twocounts. counts.First Firstisisthe thelabel labelofofbeing being lazy, lazy,based basedon onaanight nightowl’s owl’swont wonttotowake wakeup uplater laterininthe theday, day,due duetotothe the fact factthat thatthey theydid didnot notfall fallasleep asleepuntil untilthe theearly-morning early-morninghours. hours.OthOthers ers(usually (usuallymorning morninglarks) larks)will willchastise chastisenight nightowls owlson onthe theerroneous erroneous assumption assumptionthat thatsuch suchpreferences preferencesare areaachoice, choice,and andififthey theywere werenot notso so slovenly, slovenly,they theycould couldeasily easilywake wakeup upearly. early.However, However,night nightowls owlsare arenot not owls owlsby bychoice. choice.They Theyare arebound boundtotoaadelayed delayedschedule scheduleby byunavoidable unavoidable DNA DNAhardwiring. hardwiring.ItItisisnot nottheir theirconscious consciousfault, fault,but butrather rathertheir theirgenetic genetic fate. fate.

Second Secondisisthe theengrained, engrained,un-level un-levelplaying playingfield fieldofofsociety’s society’swork work scheduling, scheduling,which whichisisstrongly stronglybiased biasedtoward towardearly earlystart starttimes timesthat thatpunpunish ishowls owlsand andfavor favorlarks. larks.Although Althoughthe thesituation situationisisimproving, improving,stanstandard dardemployment employmentschedules schedulesforce forceowls owlsinto intoan anunnatural unnaturalsleep-wake sleep-wake rhythm. rhythm.Consequently, Consequently,job jobperformance performanceofofowls owlsasasaawhole wholeisisfar farless less optimal optimalininthe themornings, mornings,and andthey theyare arefurther furtherprevented preventedfrom fromexpressexpressing ingtheir theirtrue trueperformance performancepotential potentialininthe thelate lateafternoon afternoonand andearly early evening eveningasasstandard standardwork workhours hoursend endprior priortotoits itsarrival. arrival.Most Mostunforunfortunately, tunately,owls owlsare aremore morechronically chronicallysleep-deprived, sleep-deprived,having havingtotowake wakeup up with withthe thelarks, larks,but butnot notbeing beingable abletotofall fallasleep asleepuntil untilfar farlater laterininthe theeveevening. ning.Owls Owlsare arethus thusoften oftenforced forcedtotoburn burnthe theproverbial proverbialcandle candleatatboth both ends. ends.Greater Greaterillillhealth healthcaused causedby byaalack lackofofsleep sleeptherefore thereforebefalls befallsowls, owls, including includinghigher higherrates ratesofofdepression, depression,anxiety, anxiety,diabetes, diabetes,cancer, cancer,heart heart attack, attack,and andstroke. stroke.

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InInthis thisregard, regard,aasocietal societalchange changeisisneeded, needed,offering offeringaccommodations accommodations not not dissimilar dissimilar toto those those we we make make for for other other physically physically determined determined differences differences(e.g., (e.g.,sight sightimpaired). impaired).We Werequire requiremore moresupple supplework workschedules schedules that thatbetter betteradapt adapttotoall allchronotypes, chronotypes,and andnot notjust justone oneininits itsextreme. extreme.

You Youmay maybe bewondering wonderingwhy whyMother MotherNature Naturewould wouldprogram programthis this variability variabilityacross acrosspeople. people.As Asaasocial socialspecies, species,should shouldwe wenot notall allbe besynsynchronized chronizedand andtherefore thereforeawake awakeatatthe thesame sametime timetotopromote promotemaximal maximal human humaninteractions? interactions?Perhaps Perhapsnot. not.As Aswe’ll we’lldiscover discoverlater laterininthis thisbook, book, humans humanslikely likelyevolved evolvedtotoco-sleep co-sleepasasfamilies familiesororeven evenwhole wholetribes, tribes, not notalone aloneororasascouples. couples.Appreciating Appreciatingthis thisevolutionary evolutionarycontext, context,the the benefits benefits ofof such such genetically genetically programmed programmed variation variation inin sleep/wake sleep/wake timing timingpreferences preferencescan canbe beunderstood. understood.The Thenight nightowls owlsininthe thegroup group would wouldnot notbe begoing goingtotosleep sleepuntil untilone oneorortwo twoa.m., a.m.,and andnot notwaking waking until untilnine nineororten tena.m. a.m.The Themorning morninglarks, larks,on onthe theother otherhand, hand,would would have haveretired retiredfor forthe thenight nightatatnine ninep.m. p.m.and andwoken wokenatatfive fivea.m. a.m.ConseConsequently, quently,the thegroup groupasasaawhole wholeisisonly onlycollectively collectivelyvulnerable vulnerable(i.e., (i.e.,every every person personasleep) asleep)for forjust justfour fourrather ratherthan thaneight eighthours, hours,despite despiteeveryone everyone still stillgetting gettingthe thechance chancefor foreight eighthours hoursofofsleep. sleep.That’s That’spotentially potentiallyaa50 50 percent percentincrease increaseininsurvival survivalfitness. fitness.Mother MotherNature Naturewould wouldnever neverpass pass on onaabiological biologicaltrait—here, trait—here,the theuseful usefulvariability variabilityininwhen whenindividuals individuals within withinaacollective collectivetribe tribego gototosleep sleepand andwake wakeup—that up—thatcould couldenhance enhance the thesurvival survivalsafety safetyand andthus thusfitness fitnessofofaaspecies speciesby bythis thisamount. amount.And And so soshe shehasn’t. hasn’t.

MELATONIN MELATONIN Your Yoursuprachiasmatic suprachiasmaticnucleus nucleuscommunicates communicatesits itsrepeating repeatingsignal signalofof night nightand andday daytotoyour yourbrain brainand andbody bodyusing usingaacirculating circulatingmessenger messenger called calledmelatonin. melatonin.Melatonin Melatoninhas hasother othernames, names,too. too.These Theseinclude include“the “the hormone hormoneofofdarkness” darkness”and and“the “thevampire vampirehormone. hormone.” ”Not Notbecause becauseititisis sinister, sinister,but butsimply simplybecause becausemelatonin melatoninisisreleased releasedatatnight. night.Instructed Instructed by bythe thesuprachiasmatic suprachiasmaticnucleus, nucleus,the therise riseininmelatonin melatoninbegins beginssoon soon after afterdusk, dusk,being beingreleased releasedinto intothe thebloodstream bloodstreamfrom fromthe thepineal pinealgland, gland, an anarea areasituated situateddeep deepininthe theback backofofyour yourbrain. brain.Melatonin Melatoninacts actslike like aapowerful powerfulbullhorn, bullhorn,shouting shoutingout outaaclear clearmessage messagetotothe thebrain brainand and body: body:“It’s “It’sdark, dark,it’s it’sdark!” dark!”At Atthis thismoment, moment,we wehave havebeen beenserved servedaawrit writ

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MATTHEW MATTHEW WALKER WALKER

ofofnightime, nightime,and andwith withit,it,aabiological biologicalcommand commandfor forthe thetiming timingofofsleep sleep onset.* onset.* InInthis thisway, way,melatonin melatoninhelps helpsregulate regulatethe thetiming timingofofwhen whensleep sleepoccurs occurs by bysystemically systemicallysignaling signalingdarkness darknessthroughout throughoutthe theorganism. organism.But Butmelamelatonin toninhas haslittle littleinfluence influenceon onthe thegeneration generationofofsleep sleepitself: itself:aamistaken mistaken assumption assumption that that many many people people hold. hold. To To make make clear clear this this distinction, distinction, think thinkofofsleep sleepasasthe theOlympic Olympic100-meter 100-meterrace. race.Melatonin Melatoninisisthe thevoice voice ofofthe thetiming timingofficial officialthat thatsays says“Runners, “Runners,on onyour yourmark, mark, ” ”and andthen thenfires fires the thestarting startingpistol pistolthat thattriggers triggersthe therace. race.That Thattiming timingofficial official(melatonin) (melatonin) governs governswhen whenthe therace race(sleep) (sleep)begins, begins,but butdoes doesnot notparticipate participateininthe the race. race.InInthis thisanalogy, analogy,the thesprinters sprintersthemselves themselvesare areother otherbrain brainregions regions and and processes processes that that actively actively generate generate sleep. sleep. Melatonin Melatonin corrals corrals these these sleep-generating sleep-generatingregions regionsofofthe thebrain braintotothe thestarting startingline lineofofbedtime. bedtime.

Melatonin Melatoninsimply simplyprovides providesthe theofficial officialinstruction instructiontotocommence commencethe the event eventofofsleep, sleep,but butdoes doesnot notparticipate participateininthe thesleep sleeprace raceitself. itself.

For For these these reasons, reasons, melatonin melatonin isis not not aa powerful powerful sleeping sleeping aid aid inin and andofofitself, itself,atatleast leastnot notfor forhealthy, healthy,non-jet-lagged non-jet-laggedindividuals individuals(we’ll (we’ll explore explorejet jetlag—and lag—andhow howmelatonin melatonincan canbe behelpful—in helpful—inaamoment). moment).

There Theremay maybe belittle, little,ififany, any,quality qualitymelatonin melatoninininthe thepill. pill.That Thatsaid, said,there there isisaasignificant significantsleep sleepplacebo placeboeffect effectofofmelatonin, melatonin,which whichshould shouldnot notbe be underestimated: underestimated:the theplacebo placeboeffect effectis,is,after afterall, all,the themost mostreliable reliableeffect effect ininall allofofpharmacology. pharmacology.Equally Equallyimportant importanttotorealize realizeisisthe thefact factthat that over-the-counter over-the-countermelatonin melatoninisisnot notcommonly commonlyregulated regulatedby bygoverning governing bodies bodiesaround aroundthe theworld, world,such suchasasthe theUS USFood Foodand andDrug DrugAdminisAdministration tration(FDA).

(FDA).Scientific Scientificevaluations evaluationsofofover-the-counter over-the-counterbrands brandshave have found foundmelatonin melatoninconcentrations concentrationsthat thatrange rangefrom from83 83percent percentless lessthan than that thatclaimed claimedon onthe thelabel, label,toto478 478percent percentmore morethan thanthat thatstated. stated.† † Once Oncesleep sleepisisunder underway, way,melatonin melatoninslowly slowlydecreases decreasesininconcentration concentration across acrossthe thenight nightand andinto intothe themorning morninghours. hours.With Withdawn, dawn,asassunlight sunlight enters entersthe thebrain brainthrough throughthe theeyes eyes(even (eventhrough throughthe theclosed closedlids), lids),aabrake brake pedal pedalisisapplied appliedtotothe thepineal pinealgland, gland,thereby therebyshutting shuttingoff offthe therelease releaseofof melatonin. melatonin.The Theabsence absenceofofcirculating circulatingmelatonin melatoninnow nowinforms informsthe thebrain brain *For *Fornocturnal nocturnalspecies specieslike likebats, bats,crickets, crickets,fireflies, fireflies,ororfoxes, foxes,this thiscall callhappens happensininthe themorning. morning. †† L.L.A.A.Erland Erlandand andP.P.K.K.Saxena, Saxena,“Melatonin “Melatoninnatural naturalhealth healthproducts productsand andsupplements: supplements:prespresence enceofofserotonin serotoninand andsignificant significantvariability variabilityofofmelatonin melatonincontent, content, ” ”Journal JournalofofClinical ClinicalSleep Sleep Medicine Medicine2017;13(2):275–81.

2017;13(2):275–81.

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and andbody bodythat thatthe thefinish finishline lineofofsleep sleephas hasbeen beenreached. reached.ItItisistime timetotocall call the therace raceofofsleep sleepover overand andallow allowactive activewakefulness wakefulnesstotoreturn returnfor forthe therest rest ofofthe theday. day.InInthis thisregard, regard,we wehuman humanbeings beingsare are“solar “solarpowered. powered. ” ”Then, Then, asaslight lightfades, fades,so, so,too, too,does doesthe thesolar solarbrake brakepedal pedalblocking blockingmelatonin. melatonin.

As Asmelatonin melatoninrises, rises,another anotherphase phaseofofdarkness darknessisissignaled signaledand andanother another sleep sleepevent eventisiscalled calledtotothe thestarting startingline. line.

You Youcan cansee seeaatypical typicalprofile profileofofmelatonin melatoninrelease releaseininfigure figure2.2.ItItstarts starts aafew fewhours hoursafter afterdusk. dusk.Then Thenititrapidly rapidlyrises, rises,peaking peakingaround aroundfour foura.m. a.m.

Thereafter, Thereafter, ititbegins beginstotodrop dropasasdawn dawnapproaches, approaches, falling falling totolevels levelsthat that WhyWeSleep_TO_2_melatonin.pdf WhyWeSleep_TO_2_melatonin.pdf 1 1 5/11/17 5/11/17 10:29 10:29AM AM are areundetectable undetectableby byearly earlytotomidmorning. midmorning.

Figure Figure2:2:The TheCycle CycleofofMelatonin Melatonin

Melatonin (pg/mL plasma) Melatonin (pg/mL plasma)

5050 4040 3030 2020 1010 00

Noon Noon 66pm pm Midnight Midnight 66am am Noon Noon Time Time

HAVE HAVE RHYTHM, RHYTHM, WON’T WON’T TRAVEL TRAVEL The Theadvent adventofofthe thejet jetengine enginewas wasaarevolution revolutionfor forthe themass masstransit transitofof human humanbeings beingsaround aroundthe theplanet. planet.However, However,ititcreated createdan anunforeseen unforeseenbiobiological logicalcalamity: calamity:jet jetplanes planesoffered offeredthe theability abilitytotospeed speedthrough throughtime timezones zones faster fasterthan thanour ourtwenty-four-hour twenty-four-hourinternal internalclocks clockscould couldever everkeep keepup upwith with ororadjust adjustto. to.Those Thosejets jetscaused causedaabiological biologicaltime timelag: lag:jet jetlag. lag.As Asaaresult, result,we we feel feeltired tiredand andsleepy sleepyduring duringthe theday dayininaadistant distanttime timezone zonebecause becauseour our internal internalclock clockstill stillthinks thinksititisisnighttime. nighttime.ItIthasn’t hasn’tyet yetcaught caughtup. up.IfIfthat that were werenot notbad badenough, enough,atatnight, night,we weare arefrequently frequentlyunable unabletotoinitiate initiateoror maintain maintainsleep sleepbecause becauseour ourinternal internalclock clocknow nowbelieves believesitittotobe bedaytime. daytime.

Take Takethe theexample exampleofofmy myrecent recentflight flighthome hometotoEngland Englandfrom fromSan San Francisco.

Francisco.London Londonisiseight eighthours hoursahead aheadofofSan SanFrancisco.

Francisco.When WhenI Iarrive arrive

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MATTHEW MATTHEW WALKER WALKER

inin England, England, despite despite the the digital digital clock clock inin London’s London’s Heathrow Heathrow Airport Airport telling tellingme meititisisnine ninea.m., a.m.,my myinternal internalcircadian circadianclock clockisisregistering registeringaa very verydifferent differenttime—California time—Californiatime, time,which whichisisone onea.m. a.m.I Ishould shouldbe befast fast asleep. asleep.I Iwill willdrag dragmy mytime-lagged time-laggedbrain brainand andbody bodythrough throughthe theLondon London day dayininaastate stateofofdeep deeplethargy. lethargy.Every Everyaspect aspectofofmy mybiology biologyisisdemanding demanding sleep; sleep;sleep sleepthat thatmost mostpeople peopleback backininCalifornia Californiaare arebeing beingswaddled swaddledinin atatthis thistime. time.

The Theworst, worst,however, however,isisyet yettotocome. come.By Bymidnight midnightLondon Londontime, time,I I am amininbed, bed,tired tiredand andwanting wantingtotofall fallasleep. asleep.But Butunlike unlikemost mostpeople peopleinin London, London,I Ican’t can’tseem seemtotodrift driftoff. off.Though Thoughititisismidnight midnightininLondon, London,my my internal internalbiological biologicalclock clockbelieves believesitittotobe befour fourp.m., p.m.,which whichititisisininCaliCalifornia. fornia.I Iwould wouldnormally normallybe bewide wideawake, awake,and andso soI Iam, am,lying lyingininbed bedinin London.

London.ItItwill willbe befive fiveororsix sixhours hoursbefore beforemy mynatural naturaltendency tendencytotofall fall asleep asleeparrives . . . arrives . . .just justasasLondon Londonisisstarting startingtotowake wakeup, up,and andI Ihave havetotogive give aapublic publiclecture. lecture.What Whataamess. mess.

This Thisisisjet jetlag: lag:you youfeel feeltired tiredand andsleepy sleepyduring duringthe theday dayininthe thenew newtime time zone zonebecause becauseyour yourbody bodyclock clockand andassociated associatedbiology biologystill still“think” “think”ititisis nighttime. nighttime.At Atnight, night,you youare arefrequently frequentlyunable unabletotosleep sleepsolidly solidlybecause because your yourbiological biologicalrhythm rhythmstill stillbelieves believesitittotobe bedaytime. daytime.

Fortunately, Fortunately,my mybrain brainand andbody bodywill willnot notstay stayininthis thismismatched mismatched limbo limboforever. forever.I Iwill willacclimatize acclimatizetotoLondon Londontime timeby byway wayofofthe thesunlight sunlight signals signalsininthe thenew newlocation. location.But Butit’s it’saaslow slowprocess. process.For Forevery everyday dayyou youare are ininaadifferent differenttime timezone, zone,your yoursuprachiasmatic suprachiasmaticnucleus nucleuscan canonly onlyrereadjust adjust by byabout aboutone onehour. hour.ItIttherefore thereforetook tookme meabout abouteight eightdays daystotoreadjust readjust totoLondon Londontime timeafter afterhaving havingbeen beenininSan SanFrancisco, Francisco,since sinceLondon Londonisis eight eighthours hoursahead aheadofofSan SanFrancisco.

Francisco.Sadly, Sadly,after aftersuch suchepic epicefforts effortsby bymy my suprachiasmatic suprachiasmaticnucleus’s nucleus’stwenty-four-hour twenty-four-hourclock clocktotodrag dragitself itselfforward forward inintime timeand andget getsettled settledininLondon, London,ititfaces facessome somedepressing depressingnews: news:I Inow now have havetotofly flyback backtotoSan SanFrancisco Franciscoafter afternine ninedays. days.My Mypoor poorbiological biological clock clockhas hastotosuffer sufferthis thisstruggle struggleall allover overagain againininthe thereverse reversedirection! direction!

You Youmay mayhave havenoticed noticedthat thatititfeels feelsharder hardertotoacclimate acclimatetotoaanew newtime time zone zonewhen whentraveling travelingeastward eastwardthan thanwhen whenflying flyingwestward. westward.There Thereare are atatleast leasttwo tworeasons reasonsfor forthis. this.First, First,the theeastward eastwarddirection directionrequires requiresthat that you youfall fallasleep asleepearlier earlierthan thanyou youwould wouldnormally, normally,which whichisisaatall tallbiological biological order orderfor forthe themind mindtotosimply simplywill willinto intoaction. action.InIncontrast, contrast,the thewestward westward direction directionrequires requiresyou youtotostay stayup uplater, later,which whichisisaaconsciously consciouslyand andpragprag-

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matically maticallyeasier easierprospect. prospect.Second, Second,you youwill willremember rememberthat thatwhen whenshut shut off offfrom fromany anyoutside outsideworld worldinfluences, influences,our ournatural naturalcircadian circadianrhythm rhythm isisinnately innatelylonger longerthan thanone oneday—about day—abouttwenty-four twenty-fourhours hoursand andfifteen fifteen minutes. minutes.Modest Modestasasthis thismay maybe, be,this thismakes makesititsomewhat somewhateasier easierfor foryou you totoartificially artificiallystretch stretchaaday daythan thanshrink shrinkit.it.When Whenyou youtravel travelwestward— westward— ininthe thedirection directionofofyour yourinnately innatelylonger longerinternal internalclock—that clock—that“day” “day”isis longer longerthan thantwenty-four twenty-fourhours hoursfor foryou youand andwhy whyititfeels feelsaalittle littleeasier easiertoto accommodate accommodateto. to.Eastward Eastwardtravel, travel,however, however,which whichinvolves involvesaa“day” “day”that that isisshorter shorterininlength lengthfor foryou youthan thantwenty-four twenty-fourhours, hours,goes goesagainst againstthe the grain grainofofyour yourinnately innatelylong longinternal internalrhythm rhythmtotostart startwith, with,which whichisiswhy why ititisisrather ratherharder hardertotodo. do.

West Westororeast, east,jet jetlag lagstill stillplaces placesaatorturous torturousphysiological physiologicalstrain strainon on the thebrain, brain,and andaadeep deepbiological biologicalstress stressupon uponthe thecells, cells,organs, organs,and andmajor major systems systemsofofthe thebody. body.And Andthere thereare areconsequences. consequences.Scientists Scientistshave havestudstudied iedairplane airplanecabin cabincrews crewswho whofrequently frequentlyfly flyon onlong-haul long-haulroutes routesand and have havelittle littlechance chancetotorecover. recover.Two Twoalarming alarmingresults resultshave haveemerged. emerged.First, First, parts partsofoftheir theirbrains—specifically brains—specificallythose thoserelated relatedtotolearning learningand andmemmemory—had ory—hadphysically physicallyshrunk, shrunk,suggesting suggestingthe thedestruction destructionofofbrain braincells cells caused causedby bythe thebiological biologicalstress stressofoftime-zone time-zonetravel. travel.Second, Second,their theirshortshortterm termmemory memorywas wassignificantly significantlyimpaired. impaired.They Theywere wereconsiderably considerablymore more forgetful forgetfulthan thanindividuals individualsofofsimilar similarage ageand andbackground backgroundwho whodid didnot not frequently frequentlytravel travelthrough throughtime timezones. zones.Other Otherstudies studiesofofpilots, pilots,cabin cabincrew crew members, members,and andshift shiftworkers workershave havereported reportedadditionally additionallydisquieting disquietingconconsequences, sequences,including includingfar farhigher higherrates ratesofofcancer cancerand andtype type22diabetes diabetesthan than the thegeneral generalpopulation—or population—oreven evencarefully carefullycontrolled controlledmatch matchindividuals individuals who whodo donot nottravel travelasasmuch. much.

Based Basedon onthese thesedeleterious deleteriouseffects, effects,you youcan canappreciate appreciatewhy whysome some people peoplefaced facedwith withfrequent frequentjet jetlag, lag,including includingairline airlinepilots pilotsand andcabin cabin crew, crew,would wouldwant wanttotolimit limitsuch suchmisery. misery.Often, Often,they theychoose choosetototake takemelamelatonin toninpills pillsininan anattempt attempttotohelp helpwith withthe theproblem. problem.Recall Recallmy myflight flightfrom from San SanFrancisco FranciscototoLondon.

London.After Afterarriving arrivingthat thatday, day,I Ihad hadreal realdifficulty difficulty getting gettingtotosleep sleepand andstaying stayingasleep asleepthat thatnight. night.InInpart, part,this thiswas wasbecause because melatonin melatoninwas wasnot notbeing beingreleased releasedduring duringmy mynighttime nighttimeininLondon.

London.My My melatonin melatoninrise risewas wasstill stillmany manyhours hoursaway, away,back backon onCalifornia Californiatime. time.But But let’s let’simagine imaginethat thatI Iwas wasgoing goingtotouse useaalegitimate legitimatecompound compoundofofmelatomelatonin ninafter afterarriving arrivingininLondon.

London.Here’s Here’show howititworks: works:atataround aroundseven seventoto

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eight eightp.m. p.m.London Londontime timeI Iwould wouldtake takeaamelatonin melatoninpill, pill,triggering triggeringan anartiartificial ficialrise riseinincirculating circulatingmelatonin melatoninthat thatmimics mimicsthe thenatural naturalmelatonin melatonin spike spikecurrently currentlyoccurring occurringininmost mostofofthe thepeople peopleininLondon.

London.As Asaaconseconsequence, quence,my mybrain brainisisfooled fooledinto intobelieving believingit’s it’snighttime, nighttime,and andwith withthat that chemically chemicallyinduced inducedtrick trickcomes comesthe thesignaled signaledtiming timingofofthe thesleep sleeprace. race.ItIt will willstill stillbe beaastruggle struggletotogenerate generatethe theevent eventofofsleep sleepitself itselfatatthis thisirregular irregular time time( (for forme), me),but butthe thetiming timingsignal signaldoes doessignificantly significantlyincrease increasethe thelikelilikelihood hoodofofsleep sleepininthis thisjet-lagged jet-laggedcontext. context.

SLEEP SLEEP PRESSURE PRESSURE AND AND CAFFEINE CAFFEINE Your Yourtwenty-four-hour twenty-four-hourcircadian circadianrhythm rhythmisisthe thefirst firstofofthe thetwo twofactors factors determining determiningwake wakeand andsleep. sleep.The Thesecond secondisissleep sleeppressure. pressure.At Atthis thisvery very moment, moment,aachemical chemicalcalled calledadenosine adenosineisisbuilding buildingup upininyour yourbrain. brain.ItIt will willcontinue continuetotoincrease increaseininconcentration concentrationwith withevery everywaking wakingminute minute that thatelapses. elapses.The Thelonger longeryou youare areawake, awake,the themore moreadenosine adenosinewill willaccuaccumulate. mulate.Think Thinkofofadenosine adenosineasasaachemical chemicalbarometer barometerthat thatcontinuously continuously registers registersthe theamount amountofofelapsed elapsedtime timesince sinceyou youwoke wokeup upthis thismorning. morning.

One Oneconsequence consequenceofofincreasing increasingadenosine adenosineininthe thebrain brainisisan anincreasincreasing ingdesire desiretotosleep. sleep.This Thisisisknown knownasassleep sleeppressure, pressure,and andititisisthe thesecond second force forcethat thatwill willdetermine determinewhen whenyou youfeel feelsleepy, sleepy,and andthus thusshould shouldgo gototo bed. bed.Using Usingaaclever cleverdual-action dual-actioneffect, effect,high highconcentrations concentrationsofofadenosine adenosine simultaneously simultaneouslyturn turndown downthe the“volume” “volume”ofofwake-promoting wake-promotingregions regionsinin the thebrain brainand andturn turnup upthe thedial dialon onsleep-inducing sleep-inducingregions. regions.As Asaaresult resultofof that thatchemical chemicalsleep sleeppressure, pressure,when whenadenosine adenosineconcentrations concentrationspeak, peak,an an irresistible irresistibleurge urgefor forslumber slumberwill willtake takehold.* hold.*ItIthappens happenstotomost mostpeople people after aftertwelve twelvetotosixteen sixteenhours hoursofofbeing beingawake. awake.

You Youcan, can,however, however,artificially artificiallymute mutethe thesleep sleepsignal signalofofadenosine adenosineby by using usingaachemical chemicalthat thatmakes makesyou youfeel feelmore morealert alertand andawake: awake:caffeine. caffeine.

Caffeine Caffeineisisnot notaafood foodsupplement. supplement.Rather, Rather,caffeine caffeineisisthe themost mostwidely widely used used(and (andabused) abused)psychoactive psychoactivestimulant stimulantininthe theworld. world.ItItisisthe thesecond second most mosttraded tradedcommodity commodityon onthe theplanet, planet,after afteroil. oil.The Theconsumption consumptionofof caffeine caffeinerepresents representsone oneofofthe thelongest longestand andlargest largestunsupervised unsuperviseddrug drug *Assuming *Assumingyou youhave haveaastable stablecircadian circadianrhythm, rhythm,and andhave havenot notrecently recentlyexperienced experiencedjet jet travel travelthrough throughnumerous numeroustime timezones, zones,ininwhich whichcase caseyou youcan canstill stillhave havedifficulty difficultyfalling falling asleep asleepeven evenififyou youhave havebeen beenawake awakefor forsixteen sixteenhours. hours.

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studies studiesever everconducted conductedon onthe thehuman humanrace, race,perhaps perhapsrivaled rivaledonly onlyby by alcohol, alcohol,and andititcontinues continuestotothis thisday. day.

Caffeine Caffeineworks worksby bysuccessfully successfullybattling battlingwith withadenosine adenosinefor forthe thepriviprivilege legeofoflatching latchingon ontotoadenosine adenosinewelcome welcomesites—or sites—orreceptors—in receptors—inthe the brain. brain.Once Oncecaffeine caffeineoccupies occupiesthese thesereceptors, receptors,however, however,ititdoes doesnot notstimstimulate ulatethem themlike likeadenosine, adenosine,making makingyou yousleepy. sleepy.Rather, Rather,caffeine caffeineblocks blocks and andeffectively effectivelyinactivates inactivatesthe thereceptors, receptors,acting actingasasaamasking maskingagent. agent.It’s It’s the theequivalent equivalentofofsticking stickingyour yourfingers fingersininyour yourears earstotoshut shutout outaasound. sound.

By Byhijacking hijackingand andoccupying occupyingthese thesereceptors, receptors,caffeine caffeineblocks blocksthe thesleepisleepiness nesssignal signalnormally normallycommunicated communicatedtotothe thebrain brainby byadenosine. adenosine.The The upshot: upshot:caffeine caffeinetricks tricksyou youinto intofeeling feelingalert alertand andawake, awake,despite despitethe thehigh high levels levelsofofadenosine adenosinethat thatwould wouldotherwise otherwiseseduce seduceyou youinto intosleep. sleep.

Levels Levels ofof circulating circulating caffeine caffeine peak peak approximately approximately thirty thirty minutes minutes after afteroral oraladministration. administration.What Whatisisproblematic, problematic,though, though,isisthe thepersispersistence tenceofofcaffeine caffeineininyour yoursystem. system.InInpharmacology, pharmacology,we weuse usethe theterm term “half-life” “half-life”when whendiscussing discussingaadrug’s drug’sefficacy. efficacy.This Thissimply simplyrefers referstotothe the length lengthofoftime timeitittakes takesfor forthe thebody bodytotoremove remove50 50percent percentofofaadrug’s drug’sconconcentration. centration.Caffeine Caffeinehas hasan anaverage averagehalf-life half-lifeofoffive fivetotoseven sevenhours. hours.Let’s Let’s say saythat thatyou youhave haveaacup cupofofcoffee coffeeafter afteryour yourevening eveningdinner, dinner,around around7:30 7:30 p.m. p.m.This Thismeans meansthat thatby by1:30 1:30a.m., a.m.,50 50percent percentofofthat thatcaffeine caffeinemay maystill still be beactive activeand andcirculating circulatingthroughout throughoutyour yourbrain braintissue. tissue.InInother otherwords, words, by by1:30 1:30a.m., a.m.,you’re you’reonly onlyhalfway halfwaytotocompleting completingthe thejob jobofofcleansing cleansingyour your brain brainofofthe thecaffeine caffeineyou youdrank drankafter afterdinner. dinner.

There’s There’snothing nothingbenign benignabout aboutthat that50 50percent percentmark, mark,either. either.Half Halfaa shot shotofofcaffeine caffeineisisstill stillplenty plentypowerful, powerful,and andmuch muchmore moredecomposition decomposition work worklies liesahead aheadthroughout throughoutthe thenight nightbefore beforecaffeine caffeinedisappears. disappears.Sleep Sleep will willnot notcome comeeasily easilyororbe besmooth smooththroughout throughoutthe thenight nightasasyour yourbrain brain continues continuesits itsbattle battleagainst againstthe theopposing opposingforce forceofofcaffeine. caffeine.Most Mostpeople people do donot notrealize realizehow howlong longitittakes takestotoovercome overcomeaasingle singledose doseofofcaffeine, caffeine, and andtherefore thereforefail failtotomake makethe thelink linkbetween betweenthe thebad badnight nightofofsleep sleepwe we wake wakefrom fromininthe themorning morningand andthe thecup cupofofcoffee coffeewe wehad hadten tenhours hoursearlier earlier with withdinner. dinner.

Caffeine—which Caffeine—whichisisnot notonly onlyprevalent prevalentinincoffee, coffee,certain certainteas, teas,and and many manyenergy energydrinks, drinks,but butalso alsofoods foodssuch suchasasdark darkchocolate chocolateand andice ice cream, cream,asaswell wellasasdrugs drugssuch suchasasweight-loss weight-losspills pillsand andpain painrelievers— relievers— isisaacommon commonculprit culpritthat thatkeeps keepspeople peoplefrom fromfalling fallingasleep asleepeasily easilyand and

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sleeping sleepingsoundly soundlythereafter, thereafter,typically typicallymasquerading masqueradingasasinsomnia, insomnia,an an actual actualmedical medicalcondition. condition.Also Alsobe beaware awarethat thatde-caffeinated de-caffeinateddoes doesnot not mean meannon-caffeinated. non-caffeinated.Depending Dependingon onthe thedecaffeination decaffeinationmethod methodand and the thebean beanthat thatisisused, used,one onecup cupofofdecaf decafcan canhave havebetween between33totoasashigh highasas 10 10percent percentofofthe thedose doseofofaaregular regularcup cupofofcoffee. coffee.

The The“jolt” “jolt”ofofcaffeine caffeinedoes doeswear wearoff. off.Caffeine Caffeineisisremoved removedfrom fromyour your system systemby byan anenzyme enzymewithin withinyour yourliver,* liver,*which whichgradually graduallydegrades degradesitit somepeople peoplehave haveaamore more over overtime. time.Based Basedininlarge largepart parton ongenetics, genetics,† †some efficient efficientversion versionofofthe theenzyme enzymethat thatdegrades degradescaffeine, caffeine,allowing allowingthe the liver livertotorapidly rapidlyclear clearititfrom fromthe thebloodstream. bloodstream.Others, Others,however, however,have haveaa slower-acting slower-actingversion versionofofthe theenzyme. enzyme.ItIttakes takesfar farlonger longerfor fortheir theirsystem system totoeliminate eliminatethe thesame sameamount amountofofcaffeine. caffeine.As Asaaresult, result,they theyare arevery verysensensitive sitivetotocaffeine’s caffeine’seffects. effects.One Onecup cupofoftea teaororcoffee coffeeininthe themorning morningwill will last lastmuch muchofofthe theday, day,and andshould shouldthey theyhave haveaasecond secondcup, cup,even evenearly early ininthe theafternoon, afternoon,they theywill willfind findititdifficult difficulttotofall fallasleep asleepininthe theevening. evening.

Aging Agingalso alsoalters altersthe thespeed speedofofcaffeine caffeineclearance: clearance:the theolder olderwe weare, are,the the longer longeritittakes takesour ourbrain brainand andbody bodytotoremove removecaffeine, caffeine,and andthus thusthe themore more sensitive sensitivewe webecome becomeininlater laterlife lifetotocaffeine’s caffeine’ssleep-disrupting sleep-disruptinginfluence. influence.

IfIfyou youare aretrying tryingtotostay stayawake awakelate lateinto intothe thenight nightby bydrinking drinkingcofcoffee, fee,you youshould shouldbe beprepared preparedfor foraanasty nastyconsequence consequencewhen whenyour yourliver liver successfully successfullyevicts evictsthe thecaffeine caffeinefrom fromyour yoursystem: system:aaphenomenon phenomenoncomcommonly monlyknown knownasasaa“caffeine “caffeinecrash. crash. ” ”Like Likethe thebatteries batteriesrunning runningdown downon on aatoy toyrobot, robot,your yourenergy energylevels levelsplummet plummetrapidly. rapidly.You Youfind findititdifficult difficulttoto function functionand andconcentrate, concentrate,with withaastrong strongsense senseofofsleepiness sleepinessonce onceagain. again.

We Wenow nowunderstand understandwhy. why.For Forthe theentire entiretime timethat thatcaffeine caffeineisisininyour your system, system,the thesleepiness sleepinesschemical chemicalititblocks blocks(adenosine) (adenosine)nevertheless neverthelessconcontinues tinuestotobuild buildup. up.Your Yourbrain brainisisnot notaware awareofofthis thisrising risingtide tideofofsleepsleepencouraging encouragingadenosine, adenosine,however, however,because becausethe thewall wallofofcaffeine caffeineyou’ve you’ve created createdisisholding holdingititback backfrom fromyour yourperception. perception.But Butonce onceyour yourliver liver dismantles dismantlesthat thatbarricade barricadeofofcaffeine, caffeine,you youfeel feelaavicious viciousbacklash: backlash:you you *There *There are are other other factors factors that that contribute contribute toto caffeine caffeine sensitivity, sensitivity, such such asas age, age, other other medications medicationscurrently currentlybeing beingtaken, taken,and andthe thequantity quantityand andquality qualityofofprior priorsleep. sleep.A.A.Yang, Yang, A.A.A.A.Palmer, Palmer,and andH.H.dedeWit, Wit,“Genetics “Geneticsofofcaffeine caffeineconsumption consumptionand andresponses responsestotocafcaffeine, feine, ” ”Psychopharmacology Psychopharmacology311, 311,no. no.33(2010): (2010):245–57, 245–57,http://www.ncbi.nlm.nih.gov/pmc/ http://www.ncbi.nlm.nih.gov/pmc/ articles/PMC4242593/. articles/PMC4242593/. †† The Theprincipal principalliver liverenzyme enzymethat thatmetabolizes metabolizescaffeine caffeineisiscalled calledcytochrome cytochromeP450 P4501A2.

1A2.

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are arehit hitwith withthe thesleepiness sleepinessyou youhad hadexperienced experiencedtwo twoororthree threehours hoursago ago before beforeyou youdrank drankthat thatcup cupcoffee coffeeplus plusall allthe theextra extraadenosine adenosinethat thathas has accumulated accumulatedininthe thehours hoursininbetween, between,impatiently impatientlywaiting waitingfor forcaffeine caffeine totoleave. leave.When Whenthe thereceptors receptorsbecome becomevacant vacantby byway wayofofcaffeine caffeinedecomdecomposition, position,adenosine adenosinerushes rushesback backininand andsmothers smothersthe thereceptors. receptors.When When this thishappens, happens,you youare areassaulted assaultedwith withaamost mostforceful forcefuladenosine-trigger adenosine-trigger urge urgetotosleep—the sleep—theaforementioned aforementionedcaffeine caffeinecrash. crash.Unless Unlessyou youconsume consume even evenmore morecaffeine caffeinetotopush pushback backagainst againstthe theweight weightofofadenosine, adenosine,which which would wouldstart startaadependency dependencycycle, cycle,you youare aregoing goingtotofind findititvery, very,very verydifdifficult ficulttotoremain remainawake. awake.

To To impress impress upon upon you you the the effects effects ofof caffeine, caffeine, I I footnote footnote esoteric esoteric research researchconducted conductedininthe the1980s 1980sby byNASA. NASA.Their Theirscientists scientistsexposed exposedspispiders derstotodifferent differentdrugs drugsand andthen thenobserved observedthe thewebs websthat thatthey theyconstructconstructed.* ed.*Those Thosedrugs drugsincluded includedLSD, LSD,speed speed(amphetamine), (amphetamine),marijuana, marijuana,and and caffeine. caffeine.The Theresults, results,which whichspeak speakfor forthemselves, themselves,can canbe beobserved observedinin figure figure3.3.The Theresearchers researchersnoted notedhow howstrikingly strikinglyincapable incapablethe thespiders spiders WhyWeSleep_TO_3_effects.pdf WhyWeSleep_TO_3_effects.pdf 1 1 3/16/17 3/16/17aa10:40 10:40 AM AM or were wereininconstructing constructing anything anythingresembling resembling normal normal orlogical logicalweb webthat that would wouldbe beofofany anyfunctional functionaluse usewhen whengiven givencaffeine, caffeine,even evenrelative relativetoto other otherpotent potentdrugs drugstested. tested.

Figure Figure3:3:Effects EffectsofofVarious VariousDrugs Drugson onSpider SpiderWeb WebBuilding Building Normal Normal

LSD LSD

Speed Speed

Marijuana Marijuana

Caffeine Caffeine

ItItisisworth worthpointing pointingout outthat thatcaffeine caffeineisisaastimulant stimulantdrug. drug.Caffeine Caffeineisis also alsothe theonly onlyaddictive addictivesubstance substancethat thatwe wereadily readilygive givetotoour ourchildren childrenand and teens—the teens—theconsequences consequencesofofwhich whichwe wewill willreturn returntotolater laterininthe thebook. book.

*R. *R.Noever, Noever,J. J.Cronise, Cronise,and andR.R.A.A.Relwani, Relwani,“Using “Usingspider-web spider-webpatterns patternstotodetermine determinetoxictoxicity, ity, ” ”NASA NASATech TechBriefs Briefs19, 19,no. no.44(1995): (1995):82; 82;and andPeter PeterN.N.Witt Wittand andJerome JeromeS.S.Rovner, Rovner,Spider Spider Communication: Communication:Mechanisms Mechanismsand andEcological EcologicalSignificance Significance(Princeton (PrincetonUniversity UniversityPress, Press,1982).

1982).

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IN IN STEP, STEP, OUT OUT OF OF STEP STEP Setting Settingcaffeine caffeineaside asidefor foraamoment, moment,you youmay mayhave haveassumed assumedthat thatthe thetwo two governing governingforces forcesthat thatregulate regulateyour yoursleep—the sleep—thetwenty-four-hour twenty-four-hourcircacircadian dianrhythm rhythmofofthe thesuprachiasmatic suprachiasmaticnucleus nucleusand andthe thesleepsleep-pressure pressure signal signalofofadenosine—communicate adenosine—communicatewith witheach eachother otherso soasastotounite unitetheir their influences. influences.InInactual actualfact, fact,they theydon’t. don’t.They Theyare aretwo twodistinct distinctand andseparate separate systems systemsthat thatare areignorant ignorantofofeach eachother. other.They Theyare arenot notcoupled; coupled;though, though, they theyare areusually usuallyaligned. aligned.

Figure Figure44encompasses encompassesforty-eight forty-eighthours hoursofoftime timefrom fromleft lefttotoright— right— two twodays daysand andtwo twonights. nights.The Thedotted dottedline lineininthe thefigure figureisisthe thecircacircadian dianrhythm, rhythm,also alsoknown knownasasProcess-C. Process-C.Like Likeaasine sinewave, wave,ititreliably reliablyand and repeatedly repeatedlyrises risesand andfalls, falls,and andthen thenrises risesand andfalls fallsonce oncemore. more.Starting Starting on onthe thefar farleft leftofofthe thefigure, figure,the thecircadian circadianrhythm rhythmbegins beginstotoincrease increaseits its activity activityaafew fewhours hoursbefore beforeyou youwake wakeup. up.ItItinfuses infusesthe thebrain brainand andbody body with withan analerting alertingenergy energysignal. signal.Think Thinkofofititlike likeaarousing rousingmarching marchingband band approaching approaching from from a a distance. distance.

At At first, first, the the signal signal is is faint, faint, but but gradually gradually WhyWeSleep_TO_4_twofactors.pdf WhyWeSleep_TO_4_twofactors.pdf 1 1 5/11/17 5/11/17 10:30 10:30AM AM ititbuilds, builds,and andbuilds, builds,and andbuilds buildswith withtime. time.By Byearly earlyafternoon afternoonininmost most healthy healthyadults, adults,the theactivating activatingsignal signalfrom fromthe thecircadian circadianrhythm rhythmpeaks. peaks.

Figure Figure4:4:The TheTwo TwoFactors FactorsRegulating RegulatingSleep Sleepand andWakefulness Wakefulness Sleep Sleepreduces reducesadenosine adenosine

(Decreasing (Decreasingsleep sleeppressure, pressure,ororProcess-S) Process-S)

Process-S Process-S

(Sleep (Sleepdrive) drive)

Process-C Process-C

Circadian Circadian (Wake (Wakedrive) drive)

7 7am am

sleep sleep 1111pm pm 7 7am am

sleep sleep 1111pm pm 7 7am am

Now Nowlet letus usconsider considerwhat whatisishappening happeningtotothe theother othersleep-controlling sleep-controlling factor: factor:adenosine. adenosine.Adenosine Adenosinecreates createsaapressure pressuretotosleep, sleep,also alsoknown knownasas Process-S. Process-S.Represented Representedby bythe thesolid solidline lineininfigure figure4,4,the thelonger longeryou youare are awake, awake,the themore moreadenosine adenosinebuilds buildsup, up,creating creatingan anincreasing increasingurge urge(pres(pressure) sure)totosleep. sleep.By Bymidmid-totolate latemorning, morning,you youhave haveonly onlybeen beenawake awakefor foraa handful handfulofofhours. hours.As Asaaresult, result,adenosine adenosineconcentrations concentrationshave haveincreased increased

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only only aa little. little. Furthermore, Furthermore, the the circadian circadian rhythm rhythm isis on on its its powerful powerful upswing upswing ofof alertness. alertness. This This combination combination ofof strong strong activating activating output output from fromthe thecircadian circadianrhythm rhythmtogether togetherwith withlow lowlevels levelsofofadenosine adenosineresult result ininaadelightful delightfulsensation sensationofofbeing beingwide wideawake. awake.(Or (Oratatleast leastititshould, should,so so long longasasyour yoursleep sleepwas wasofofgood goodquality qualityand andsufficient sufficientlength lengththe thenight night before. before.IfIfyou youfeel feelasasthough thoughyou youcould couldfall fallasleep asleepeasily easilymidmorning, midmorning, you youare arevery verylikely likelynot notgetting gettingenough enoughsleep, sleep,ororthe thequality qualityofofyour yoursleep sleep isisinsufficient.) insufficient.)The Thedistance distancebetween betweenthe thecurved curvedlines linesabove abovewill willbe beaa direct directreflection reflectionofofyour yourdesire desiretotosleep. sleep.The Thelarger largerthe thedistance distancebetween between the thetwo, two,the thegreater greateryour yoursleep sleepdesire. desire.

For Forexample, example,atateleven elevena.m., a.m.,after afterhaving havingwoken wokenup upatateight eighta.m., a.m.,there there isisonly onlyaasmall smalldistance distancebetween betweenthe thedotted dottedline line(circadian (circadianrhythm) rhythm)and and solid solidline line(sleep (sleeppressure), pressure),illustrated illustratedby bythe thevertical verticaldouble doublearrow arrowininfigfigure ure5.5.This This minimal minimaldifference differencemeans there there isisaaAMweak weaksleep sleepdrive, drive,and andaa WhyWeSleep_TO_5_urge.pdf WhyWeSleep_TO_5_urge.pdf 1means 1 5/11/17 5/11/17 10:31 10:31 AM strong strongurge urgetotobe beawake awakeand andalert. alert.

Figure Figure5:5:The TheUrge UrgetotoBe BeAwake Awake Strong Strongurge urgetotobe beawake awake

(Small (Smalldistance distancebetween betweenProcess-C Process-Cand andProcess-S) Process-S)

Process-S Process-S

(Sleep (Sleepdrive) drive)

Process-C Process-C

Circadian Circadian (Wake (Wakedrive) drive)

7 7am am

sleep sleep 1111pm pm 7 7am am

sleep sleep 1111pm pm 7 7am am

However, However,by byeleven elevenp.m. p.m.it’s it’saavery verydifferent differentsituation, situation,asasillustrated illustrated ininfigure figure6.6.You’ve You’venow nowbeen beenawake awakefor forfifteen fifteenhours hoursand andyour yourbrain brain isisdrenched drenchedininhigh highconcentrations concentrationsofofadenosine adenosine(note (notehow howthe thesolid solid line lineininthe thefigure figurehas hasrisen risensharply). sharply).InInaddition, addition,the thedotted dottedline lineofofthe the circadian circadian rhythm rhythm isis descending, descending, powering powering down down your your activity activity and and alertness alertnesslevels. levels.As Asaaresult, result,the thedifference differencebetween betweenthe thetwo twolines lineshas has grown grownlarge, large,reflected reflectedininthe thelong longvertical verticaldouble doublearrow arrowininfigure figure6.6.

This Thispowerful powerfulcombination combinationofofabundant abundantadenosine adenosine(high (highsleep sleepprespressure) sure)and anddeclining decliningcircadian circadianrhythm rhythm(lowered (loweredactivity activitylevels) levels)triggers triggers aastrong strongdesire desirefor forsleep. sleep.

WhyWeSleep_TO_6_urgetosleep.pdf WhyWeSleep_TO_6_urgetosleep.pdf

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MATTHEW MATTHEW WALKER WALKER Figure Figure6:6:The TheUrge UrgetotoSleep Sleep Greatest Greatesturge urgetotosleep sleep

(Greatest (Greatestdistance distancebetween betweenProcess-C Process-Cand andProcess-S) Process-S)

Process-S Process-S

(Sleep (Sleepdrive) drive)

Process-C Process-C

Circadian Circadian (Wake (Wakedrive) drive)

7 7am am

sleep sleep 1111pm pm 7 7am am

sleep sleep 1111pm pm 7 7am am

What Whathappens happenstotoall allofofthe theaccumulated accumulatedadenosine adenosineonce onceyou youdo dofall fall asleep? asleep?During Duringsleep, sleep,aamass massevacuation evacuationgets getsunder underway wayasasthe thebrain brain has hasthe thechance chancetotodegrade degradeand andremove removethe theday’s day’sadenosine. adenosine.Across Across the thenight, night,sleep sleeplifts liftsthe theheavy heavyweight weightofofsleep sleeppressure, pressure,lightening lighteningthe the adenosine adenosineload. load.After Afterapproximately approximatelyeight eighthours hoursofofhealthy healthysleep sleepininan an adult, adult,the theadenosine adenosinepurge purgeisiscomplete. complete.Just Justasasthis thisprocess processisisending, ending, the themarching marchingband bandofofyour yourcircadian circadianactivity activityrhythm rhythmhas hasfortuitously fortuitously returned, returned,and andits itsenergizing energizinginfluence influencestarts startstotoapproach. approach.When Whenthese these two twoprocesses processestrade tradeplaces placesininthe themorning morninghours, hours,wherein whereinadenosine adenosine has hasbeen beenremoved removedand andthe therousing rousingvolume volumeofofthe thecircadian circadianrhythm rhythmisis becoming becominglouder louder(indicated (indicatedby bythe themeeting meetingofofthe thetwo twolines linesininfigure figure6), 6), we wenaturally naturallywake wakeup up(seven (sevena.m. a.m.on onday daytwo, two,ininthe thefigure figureexample). example).FolFollowing lowingthat thatfull fullnight nightofofsleep, sleep,you youare arenow nowready readytotoface faceanother anothersixteen sixteen hours hoursofofwakefulness wakefulnesswith withphysical physicalvigor vigorand andsharp sharpbrain brainfunction. function.

INDEPENDENCE INDEPENDENCE DAY, DAY, AND AND NIGHT NIGHT Have Haveyou youever everpulled pulledan an“all-nighter”—forgoing “all-nighter”—forgoingsleep sleepand andremaining remaining awake awakethroughout throughoutthe thefollowing followingday? day?IfIfyou youhave, have,and andcan canremember remember much muchofofanything anythingabout aboutit,it,you youmay mayrecall recallthat thatthere therewere weretimes timeswhen when you youfelt felttruly trulymiserable miserableand andsleepy, sleepy,yet yetthere therewere wereother othermoments momentswhen, when, despite despitehaving havingbeen beenawake awakefor forlonger, longer,you youparadoxically paradoxicallyfelt feltmore morealert. alert.

Why? Why?I Idon’t don’tadvise adviseanyone anyonetotoconduct conductthis thisself-experiment, self-experiment,but butassessassessing ingaaperson’s person’salertness alertnessacross acrosstwenty-four twenty-fourhours hoursofoftotal totalsleep sleepdeprideprivation vationisisone oneway waythat thatscientists scientistscan candemonstrate demonstratethat thatthe thetwo twoforces forces determining determiningwhen whenyou youwant wanttotobe beawake awakeand andasleep—the asleep—thetwenty-fourtwenty-four-

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hour hour circadian circadian rhythm rhythm and and the the sleepiness sleepiness signal signal ofof adenosine—are adenosine—are independent, independent,and andcan canbe bedecoupled decoupledfrom fromtheir theirnormal normallockstep. lockstep.

Let’s Let’sconsider considerfigure figure7,7,showing showingthe thesame sameforty-eight-hour forty-eight-hourslice sliceofof time timeand andthe thetwo twofactors factorsininquestion: question:the thetwenty-four-hour twenty-four-hourcircadian circadian rhythm rhythmand andthe thesleep sleeppressure pressuresignal signalofofadenosine, adenosine,and andhow howmuch muchdisdistance tancethere thereisisbetween betweenthem. them.InInthis thisscenario, scenario,our ourvolunteer volunteerisisgoing going totostay stayawake awakeall allnight nightand andall allday. day.As Asthe thenight nightofofsleep sleepdeprivation deprivation marches marchesforward, forward,the thesleep sleeppressure pressureofofadenosine adenosine(upper (upperline) line)rises risesproprogressively, gressively,like likethe therising risingwater waterlevel levelininaaplugged pluggedsink sinkwhen whenaafaucet faucethas has WhyWeSleep_TO_7_ebbandflow.pdf WhyWeSleep_TO_7_ebbandflow.pdf 1 1 5/11/17 5/11/17 10:32 10:32 AM been beenleft left on. on.ItItwill willnot notdecline declineacross across the thenight. night.

ItItAMcannot, cannot,since sincesleep sleep isisabsent. absent.

Figure Figure7:7:The TheEbb Ebband andFlow FlowofofSleep SleepDeprivation Deprivation Overpowering Overpoweringurge urgetotosleep sleep Weak Weakurge urgetotosleep sleep Strong Strongurge urgetotosleep sleep Process-S Process-S

(Sleep (Sleepdrive) drive)

Process-C Process-C

Circadian Circadian (Wakedrive) drive) (Wake am 7 7am

awake awake sleep awake awake sleep pm 7 7am am pm 7 7am am 1111pm 1111pm

By Byremaining remainingawake, awake,and andblocking blockingaccess accesstotothe theadenosine adenosinedrain drain that thatsleep sleepopens opensup, up,the thebrain brainisisunable unabletotorid riditself itselfofofthe thechemical chemicalsleep sleep pressure. pressure.The Themounting mountingadenosine adenosinelevels levelscontinue continuetotorise. rise.This Thisshould should mean meanthat thatthe thelonger longeryou youare areawake, awake,the thesleepier sleepieryou youfeel. feel.But Butthat’s that’snot not true. true.Though Thoughyou youwill willfeel feelincreasingly increasinglysleepy sleepythroughout throughoutthe thenighttime nighttime phase, phase,hitting hittingaalow lowpoint pointininyour youralertness alertnessaround aroundfive fivetotosix sixa.m., a.m.,therethereafter, after,you’ll you’llcatch catchaasecond secondwind. wind.How Howisisthis thispossible possiblewhen whenadenosine adenosine levels levelsand andcorresponding correspondingsleep sleeppressure pressurecontinue continuetotoincrease? increase?

The Theanswer answerresides resideswith withyour yourtwenty-four-hour twenty-four-hourcircadian circadianrhythm, rhythm, which whichoffers offersaabrief briefperiod periodofofsalvation salvationfrom fromsleepiness. sleepiness.Unlike Unlikesleep sleep pressure, pressure,your yourcircadian circadianrhythm rhythmpays paysno noattention attentiontotowhether whetheryou youare are asleep asleepororawake. awake.Its Itsslow, slow,rhythmic rhythmiccountenance countenancecontinues continuestotofall falland and rise risestrictly strictlyon onthe thebasis basisofofwhat whattime timeofofnight nightororday dayititis.is.No Nomatter matter what whatstate stateofofadenosine adenosinesleepiness sleepinesspressure pressureexists existswithin withinthe thebrain, brain,the the

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MATTHEW MATTHEW WALKER WALKER

twenty-four-hour twenty-four-hourcircadian circadianrhythm rhythmcycles cycleson onasasper perusual, usual,oblivious oblivioustoto your yourongoing ongoinglack lackofofsleep. sleep.

IfIfyou youlook lookatatfigure figure77once onceagain, again,the thegraveyard-shift graveyard-shiftmisery miseryyou you experience experiencearound aroundsix sixa.m. a.m.can canbe beexplained explainedby bythe thecombination combinationofofhigh high adenosine adenosinesleep sleeppressure pressureand andyour yourcircadian circadianrhythm rhythmreaching reachingits itslowest lowest point. point.The Thevertical verticaldistance distanceseparating separatingthese thesetwo twolines linesatatthree threea.m. a.m.isis large, large,indicated indicatedby bythe thefirst firstvertical verticalarrow arrowininthe thefigure. figure.But Butififyou youcan can make makeititpast pastthis thisalertness alertnesslow lowpoint, point,you’re you’reininfor foraarally. rally.The Themorning morning rise riseofofthe thecircadian circadianrhythm rhythmcomes comestotoyour yourrescue, rescue,marshaling marshalingan analertalerting ingboost boostthroughout throughoutthe themorning morningthat thattemporarily temporarilyoffsets offsetsthe therising rising levels levelsofofadenosine adenosinesleep sleeppressure. pressure.As Asyour yourcircadian circadianrhythm rhythmhits hitsits its peak peakaround aroundeleven elevena.m., a.m.,the thevertical verticaldistance distancebetween betweenthe thetwo tworespecrespective tivelines linesininfigure figure77has hasbeen beendecreased. decreased.

The Theupshot upshotisisthat thatyou youwill willfeel feelmuch muchless lesssleepy sleepyatateleven elevena.m. a.m.than than you youdid didatatthree threea.m., a.m.,despite despitebeing beingawake awakefor forlonger. longer.Sadly, Sadly,this thissecond second wind winddoesn’t doesn’tlast. last.As Asthe theafternoon afternoonlumbers lumberson, on,the thecircadian circadianrhythm rhythm begins beginstotodecline declineasasthe theescalating escalatingadenosine adenosinepiles pileson onthe thesleep sleepprespressure. sure.Come Comelate lateafternoon afternoonand andearly earlyevening, evening,any anytemporary temporaryalertness alertness boost boosthas hasbeen beenlost. lost.You Youare arehit hitby bythe thefull fullforce forceofofan animmense immenseadeadenosine nosinesleep sleeppressure. pressure.By Bynine ninep.m., p.m.,there thereexists existsaatowering toweringvertical verticaldisdistance tancebetween betweenthe thetwo twolines linesininfigure figure7.7.Short Shortofofintravenous intravenouscaffeine caffeine ororamphetamine, amphetamine,sleep sleepwill willhave haveits itsway, way,wrestling wrestlingyour yourbrain brainfrom fromthe the now nowweak weakgrip gripofofblurry blurrywakefulness, wakefulness,blanketing blanketingyou youininslumber. slumber.

AM AM I I GETTING GETTING ENOUGH ENOUGH SLEEP? SLEEP? Setting Settingaside asidethe theextreme extremecase caseofofsleep sleepdeprivation, deprivation,how howdo doyou youknow know whether whetheryou’re you’reroutinely routinelygetting gettingenough enoughsleep? sleep?While Whileaaclinical clinicalsleep sleep assessment assessmentisisneeded neededtotothoroughly thoroughlyaddress addressthis thisissue, issue,an aneasy easyrule ruleofof thumb thumbisistotoanswer answertwo twosimple simplequestions. questions.First, First,after afterwaking wakingup upininthe the morning, morning,could couldyou youfall fallback backasleep asleepatatten tenororeleven elevena.m.? a.m.?IfIfthe theanswer answer isis“yes, “yes, ” ”you youare arelikely likelynot notgetting gettingsufficient sufficientsleep sleepquantity quantityand/or and/orqualquality. ity.Second, Second,can canyou youfunction functionoptimally optimallywithout withoutcaffeine caffeinebefore beforenoon? noon?IfIf the theanswer answerisis“no, “no, ” ”then thenyou youare aremost mostlikely likelyself-medicating self-medicatingyour yourstate stateofof chronic chronicsleep sleepdeprivation. deprivation.

Both Bothofofthese thesesigns signsyou youshould shouldtake takeseriously seriouslyand andseek seektotoaddress address

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your yoursleep sleepdeficiency. deficiency.They Theyare aretopics, topics,and andaaquestion, question,that thatwe wewill will cover coverinindepth depthininchapters chapters13 13and and14 14when whenwe wespeak speakabout aboutthe thefactors factors that thatprevent preventand andharm harmyour yoursleep, sleep,asaswell wellasasinsomnia insomniaand andeffeceffective tivetreatments. treatments.InIngeneral, general,these theseun-refreshed un-refreshedfeelings feelingsthat thatcompel compel aa person person toto fall fall back back asleep asleep midmorning, midmorning, oror require require the the boosting boosting ofofalertness alertnesswith withcaffeine, caffeine,are areusually usuallydue duetotoindividuals individualsnot notgiving giving themselves themselvesadequate adequatesleep sleepopportunity opportunitytime—at time—atleast leasteight eightorornine nine hours hoursininbed. bed.When Whenyou youdon’t don’tget getenough enoughsleep, sleep,one oneconsequence consequence among amongmany manyisisthat thatadenosine adenosineconcentrations concentrationsremain remaintoo toohigh. high.Like Like an anoutstanding outstandingdebt debton onaaloan, loan,come comethe themorning, morning,some somequantity quantity ofofyesterday’s yesterday’sadenosine adenosineremains. remains.You Youthen thencarry carrythat thatoutstanding outstanding sleepiness sleepinessbalance balancethroughout throughoutthe thefollowing followingday. day.Also Alsolike likeaaloan loaninin arrears, arrears,this thissleep sleepdebt debtwill willcontinue continuetotoaccumulate. accumulate.You Youcannot cannothide hide from fromit.it.The Thedebt debtwill willroll rollover overinto intothe thenext nextpayment paymentcycle, cycle,and andthe the next, next,and andthe thenext, next,producing producingaacondition conditionofofprolonged, prolonged,chronic chronicsleep sleep deprivation deprivationfrom fromone oneday daytotoanother. another.This Thisoutstanding outstandingsleep sleepobligaobligation tionresults resultsininaafeeling feelingofofchronic chronicfatigue, fatigue,manifesting manifestingininmany manyforms forms ofofmental mentaland andphysical physicalailments ailmentsthat thatare arenow nowrife rifethroughout throughoutindusindustrialized trializednations. nations.

Other Otherquestions questionsthat thatcan candraw drawout outsigns signsofofinsufficient insufficientsleep sleepare: are:IfIf you youdidn’t didn’tset setan analarm alarmclock, clock,would wouldyou yousleep sleeppast pastthat thattime? time?(If(Ifso, so,you you need needmore moresleep sleepthan thanyou youare aregiving givingyourself.) yourself.)Do Doyou youfind findyourself yourselfatat your yourcomputer computerscreen screenreading readingand andthen thenrereading rereading(and (andperhaps perhapsrereadrereading ingagain) again)the thesame samesentence? sentence?(This (Thisisisoften oftenaasign signofofaafatigued, fatigued,underunderslept sleptbrain.) brain.)Do Doyou yousometimes sometimesforget forgetwhat whatcolor colorthe thelast lastfew fewtraffic traffic lights lightswere werewhile whiledriving? driving?(Simple (Simpledistraction distractionisisoften oftenthe thecause, cause,but butaa lack lackofofsleep sleepisisanother anotherculprit.) culprit.)

Of Ofcourse, course,even evenififyou youare aregiving givingyourself yourselfplenty plentyofoftime timetotoget getaa full fullnight nightofofshut-eye, shut-eye,next-day next-dayfatigue fatigueand andsleepiness sleepinesscan canstill stilloccur occur because becauseyou youare aresuffering sufferingfrom froman anundiagnosed undiagnosedsleep sleepdisorder, disorder,ofofwhich which there thereare arenow nowmore morethan thanaahundred. hundred.The Themost mostcommon commonisisinsomnia, insomnia, followed followedby bysleep-disordered sleep-disorderedbreathing, breathing,ororsleep sleepapnea, apnea,which whichincludes includes heavy heavysnoring. snoring.Should Shouldyou yoususpect suspectyour yoursleep sleepororthat thatofofanyone anyoneelse else totobe bedisordered, disordered,resulting resultinginindaytime daytimefatigue, fatigue,impairment, impairment,orordistress, distress, speak speaktotoyour yourdoctor doctorimmediately immediatelyand andseek seekaareferral referraltotoaasleep sleepspespecialist. cialist.Most Mostimportant importantininthis thisregard: regard:you youmay maynot notneed needtotoseek seekout out