Shift Work Sleep Disorder

By Daniel T. Layish, MD, FACP, FCCP, FAASM

Optimal sleep and wakefulness requires proper alignment between an individual’s intrinsic circadian rhythm and their desired sleep wake schedule. The word circadian comes from the Latin “circa” meaning “about” and “dian” meaning “day”. Our intrinsic circadian rhythm is controlled by an internal clock in the hypothalamus (suprachiasmatic nucleus). The hypothalamus receives signals from the retina that entrain the circadian rhythm to the light dark cycle. The circadian rhythm affects the timing of sleep. There is also a homeostatic sleep drive, which controls sleep intensity, and it is determined by how long an individual has been awake.

of shift rotation. It may also vary depending upon a patient’s diurnal preference. It appears to be less common in individuals who identify themselves as “night owls”. Individuals with shift work sleep disorder have been found to have higher rates of peptic ulcer disease as well as more sleepiness related motor vehicle accidents. Other consequences of this disorder include absenteeism from work, higher rates of depression and missed family and social activities as well as chronic fatigue and poor work performance. There have also been studies which link shift work sleep disorder to glucose intolerance as well as higher risk for alcohol and substance use. Sleep

Shift work sleep disorder is a recurrent or persistent mismatch between a person’s habitual sleep wake schedule and their endogenous circadian rhythm. Shift work sleep disorder can be associated with insomnia or excessive sleepiness (or both). The conventional time cues (zeitgeber = “time giver” in German) of sunlight and social activities are frequently out of phase with the altered sleep schedule in an individual with shift work sleep disorder. Many shift workers revert back to their traditional daytime schedule during non-work days. By definition, the course of shift work sleep disorder parallels the period of the shift work and remits with termination of shift work. An individual with shift work sleep disorder may use a large portion of their free time for recovery of sleep, which may have negative social consequences such as marital discord and impaired social relationships. Shift work sleep disorder tends to be more common after age 50. Between 5 and 8% of the population is exposed to night work on a regular or periodic basis.

Shift work sleep disorder is usually a clinical diagnosis. A formal sleep study (polysomnogram) may be helpful to exclude other etiologies of a patient’s symptoms. The sleep study should ideally be performed during the regular hours of sleep of the individual having the study. To diagnose shift work sleep disorder one must exclude any other medical or psychiatric conditions which could account for the symptoms. In addition, the symptoms should not meet criteria for any other sleep disorder which can produce insomnia or excessive daytime sleepiness (such as Jet-lag syndrome). Women appear to be slightly more prone to developing shift work sleep disorder. Interestingly, women tend to quit their shift work less often than men. The occurrence of shift work sleep disorder may vary depending upon the speed and direction

diaries can be helpful in assessing patients with shift work sleep disorder. Actigraphy can be useful as an adjunct to history, physical exam and sleep diary. Actigraphy recording should consist of at least three consecutive 24-hour periods. Circadian rhythm markers (such as core body temperature monitoring or timing of melatonin secretion) are more difficult and typically are not used in routine clinical settings.

Treatment for shift work sleep disorder can include exposure to bright light in the work place as well as administration of wake promoting agents during evening work hours. Other treatments include scheduled napping as well as hypnotic agents to improve daytime sleep. Maintaining a regular sleep wake schedule during both work and non-work days is also recommended (as well as minimizing light or noise in the bedroom and allowing sufficient time in bed for sleep during the daytime). Other recommendations include limiting light exposure by using dark sunglasses during the morning trip home from work. The timing of light therapy is critical. The American Academy of Sleep Medicine recommends light exposure before the core temperature is reached in an individual with a morning/evening/night schedule (versus administrating light therapy after core temperature in an individual with a night/evening/morning schedule). Studies have utilized various light intensities from 2350 to 12,000 lux. Some but not all studies of bright light therapy have also restricted daytime light exposure. Different schedules of light exposure have also been used. Melatonin has both sleep promoting (hypnotic) and phase shifting properties. Melatonin (when given to night workers before their daytime sleep) may enhance daytime sleep and appears to have no effect on subsequent nighttime alertness. In a study published by Czeisler in The New England Journal of Medicine in 2005, modafinil resulted in decreased accidents/ near accidents during the commute home (versus placebo). Treatments for shift work sleep disorder can include modafinil (Provigil) as well as armodafinil (Nuvigil). These medications are nonamphetamine stimulants believed to act on the hypothalamus, although their exact mechanism of action is unknown.

Shifts can be permanent, fixed or rotating. Shift can rotate forward (clockwise) (from morning to evening to nighttime) or backward (from night to afternoon to early morning shift). Rotating shifts seem to cause more sleep difficulties than permanent shifts and counter clockwise rotation affects sleep wake activities more than clockwise rotation. The speed of rotation and the length of the shift may also impact an individual’s symptoms.

It appears that workers on permanent night shifts sleep one to four hours less than day workers and individuals on rotating shifts sleep about two hours less than day workers. There are several factors involved in this. Shift workers must try to sleep at a time when their circadian/wakefulness drive is exerting pressure on them to remain awake. The desire to spend time with family or take care of household or social obligations is also a factor. Environmental factors such as noise and light may also be obstacles to sleep quality for shift workers.

• Type of shifts (permanent, rotating).

• Duration of shifts.

• Speed of rotation (slow or fast).

• Direction of rotation (clockwise or counter clockwise).

• Social and family disruption.

• Exposure to natural or artificial light.

• Existing health problems.

• Age (over 50 is more adversely affected than younger individuals)

• Gender (female shift workers seem to have more difficulty coping with shift work than men).

In general, the circadian clock adjusts better to clockwise rotation because it is naturally easier to delay sleep to a later hour. Typically, longer shifts (such as 10-12 hours) cause more sleepiness than eight hour shifts. Women doing shift work tend to get less sleep than men when they are not working because of their persistent family and social obligations. Overall, night and rotating shift workers comprise approximately 6% of all workers. About 1% of the working population in the United States is believed to suffer from shift work disorder. Increased awareness of this disorder should allow more individuals to receive proper diagnosis and therapy.

Daniel Layish, MD, graduated magna cum laude from Boston University Medical School in 1990. He then completed an Internal Medicine Residency at Barnes Hospital (Washington University) in St.Louis, Missouri and a Pulmonary/Critical Care/Sleep Medicine Fellowship at Duke University in Durham, North Carolina. Since 1997, he has been a member of the Central Florida Pulmonary Group in Orlando. He serves as Co-director of the Adult Cystic Fibrosis Program in Orlando. He may be contacted at 407841-1100 or by visiting www.cfpulmonary.com.