Biology – is your internal clock running slow?

Do you have the time?

A closer look at our bodies’ internal clocks

Vanessa Fernandez Vidueira explores how the human body may not actually follow a 24-hour circadian cycle as previously thought, and how personal schedules could help us to become healthier and more productive.

“Early to bed and early to rise, makes a man healthy, wealthy, and wise". But wait, does it? It depends on how your internal body clock ticks. Did you know your internal clock doesn’t run on a precise 24-hour schedule?

Although it may be surprising to know that we will never have a perfect clock, the good news is there are things you can do to help your body stay on track.

Imagine you were put in an underground bunker, with nothing to tell you the time, to live in complete isolation for several weeks. Would you still be hungry, sleepy, or alert at the same times you are in your regular life? Scientists started to delve into these questions many years ago, after observing that daily leaf movements in plants prevailed even when the plants were exposed to constant darkness.

In 1938, the physiologist Nathaniel

Kleitman, and one of his students spent 32 days isolated in a cave to test the flexibility of their internal clocks.

By keeping temperature, illumination, and noise constant in the cave, and refraining from social interactions, they attempted to acclimatise to lengthy 28-hour days (9 hours sleep, 10 hours work, 9 hours leisure).

Despite the significantly longer days and the absence of any external cues, their body temperature continued to follow a cycle of around 24 hours.

However, the small sample size, difficulty to completely remove external cues, and differences in the participants’ responses resulted in the research being inconclusive.

More sophisticated experiments by

Jürgen Aschoff in the 60s confirmed that subjects in isolation still show clear cycles of body temperature, urine excretion, sleep, and wakefulness, amongst others. These cyclical patterns, which are now known to control physiological, psychological, and behavioural processes, are called “circadian rhythms” and are orchestrated by a x 20 Winter 2022 | eusci.org.uk

Illustration by Elizabeth Stroud

group of cells in the brain called the suprachiasmatic nucleus (SCN), your internal timekeeping mechanism.

While the world continued to cycle through dawn and dusk over a 24hour period, the participants in Aschoff’s bunker experiment settled into circadian rhythms closer to 25 hours. It turned out that our internal cycle is, in fact, slightly longer than 24 hours. No wonder you are always left wishing there was one more hour in the day! Although the reason for this is unknown, theories suggest that some flexibility in our “almost 24hour clock” allows for an easier adaptation to different photoperiods (day lengths).

The Earth continues to rotate inexorably with a 24-hour period. Like a watch that keeps falling behind, our bodies need to readjust everyday to the external time. They do so through external cues (termed zeitgebers - from the German word zeit meaning “time” and geber meaning “giver”) which allow them to synchronise to the natural 24-hour day. Light is the most powerful zeitgeber and regulates the release of x melatonin, the main hormone involved in the sleep-wake cycle. Other well-studied zeitgebers are meals, physical activity, and social interactions. Controlling these gives your body the right hints to know when you need to get ready to sleep or to be productive during the day.

Why can some people be up and alert at 6 am in the morning while others don’t feel rested if they don’t sleep until midday? You can probably identify yourself as an early bird, a night owl, or somewhere in between. Scientifically, a person’s natural predisposition to be asleep or awake at specific times is known as their chronotype. Your chronotype is not necessarily a product of your choice but dictated by internal biological rhythms and the consequent physiological variations such as body temperature and hormone release, which make you feel sleepy or fully alert at different times of the day.

Chronobiology research has important repercussions on a person’s health. Studies have shown, for example, that some cancer treatments have fewer side effects when x

administered at the time of day that best aligns with the patient’s internal clock. Recently, scientists have also found some aspects of immune activity to follow a circadian pattern, with immune responses being at their highest at the end of a resting period (early morning for humans). These findings could have implications for the most efficient times for vaccinations and immunotherapies.

When it comes to what is best, a healthy body clock should smoothly align with the external environment, that is, our sleep and wakefulness should be synchronised to the day and night cycle. The master clock in the SCN should also work in harmony with peripheral clocks located in other body tissues, with all of them ticking at the same rate. Any disruptions to these mechanisms could put your circadian rhythm out of sync, a disorder known as circadian misalignment. Such misalignments have been associated with an increased risk of health problems (obesity, type 2 diabetes, depression, and cardiovascular problems, amongst others).

While morning-types’ clocks can fit well to modern social schedules (such as school and work times), evening-types' internal timer is continuously fighting these social constraints, which puts night owls in a constant jet lag state. Not only do evening-types see their sleep reduced due to the early wake up times imposed by social demands, but they are also asked to be alert and perform at their best at a time of day when their bodies are not ready.

Flexible working schedules and later school start times are some of the measures which have been suggested to reduce evening-types’ disadvantages and increase performance, health, and wellbeing. Based on these recommendations, some school districts have already taken action and shifted their schedules to later start times. Improvements in academic performance and attendance rates, as well as a reduced number of car crashes in teen drivers were reported in schools with a start later than 8:35 am in a study conducted with over 9,000 students in the US.

At this point you may be wondering whether your chronotype can be changed. Although there is no definitive answer, if your parents enjoy late evenings and lie-ins, chances are you are following that pattern too. The reason is because chronotypes are mostly determined x genetically. Other factors such as age, sex, and environmental factors are involved as well. A marked shift towards eveningness is characteristic of the adolescent period, for example, and women usually show a greater tendency towards morningness. While most factors influencing your chronotype can’t be changed, using zeitgebers to help your body clock readjust daily can benefit your timekeeping machinery.

Here is how you can look after your internal clock:

1. Light exposure at the right time of day: light in the morning helps your clock to reset and increases alertness whereas minimising light exposure in the evenings (no electronic devices, dim lights, and so on) helps your body get ready to sleep.

2. Exercise but not close to bedtime.

3. Avoid caffeine late in the day and alcohol before bedtime.

While alcohol may help you to fall asleep, it decreases the quality of sleep.

4. Create a good environment for a good night’s sleep: have a power-down routine when closer to bedtime, keep your bedroom dark and the temperature low, use a good mattress and pillow, and avoid noises and distractions.

5. Try to keep bed and wake-up times consistent.

6. And probably the best piece of advice: don’t fight it.

Whenever possible, do the bulk of your work when you feel most productive, creative, awake, and rest when your body asks you to do so.

Illustration by Elizabeth Stroud

If we had ever wondered whether flexible working hours would benefit our biological rhythms and ability to synchronise with the environment, the Covid19 pandemic may have accidentally given us the answer. Increased sleep duration and decreased social jet lag have been reported during lockdowns, factors which have helped to decrease stress in some populations as well. We may not be able to change our chronotype, but we are starting to understand how personalised schedules can keep our body clocks in sync to “make us healthy, wealthy, and wise”.

Vanessa (@VanessaVidueira) is a PhD student exploring the role of chronotypes on sports performance in adolescence.