The Tick-Tock of Our Biological Clock

HE_sleep-alarm-clock_s4x3_leadWe live in a world where sleep is for the weak, but perhaps the lack of sleep is what weakens us the most. We constantly engage ourselves intellectually and socially yet undervalue the necessity of several hours of mindless sleep. We pull all-nighters weekday after weekday and try to compensate for our accumulated sleep debt by sleeping in on weekends. It is important to consider the effects of this college lifestyle on our biological clocks.

A sleep cycle is regulated by the biological clock. When all external cues (like light and alarm clocks) are taken away, our biological clocks become free-running and assume a day with a period of approximately 25 hours. But even with external cues, not all of us follow the same sleep schedule. To establish a standard measurement for sleep cycles, chronobiologists assign individuals a chronotype (midpoint of sleep) that takes into account sleep duration and sleep onset. For instance, going to bed at 12 a.m. and waking up at 10 a.m. on normal weekends gives a chronotype of 5. To give some context, 60 percent of the worldwide population has a chronotype between 3:30 and 5:30. Our chronotypes are constantly shifting during our lifespan: as we get older, our chronotype moves later and later in the day until we reach the end of adolescence, at which point we slowly return to our baseline chronotype. We essentially end life at the same chronotype we had as infants.

With this in mind, consider the time most teenagers have to get up to go to school. The 6 a.m. alarm is a huge impediment to students with late chronotypes, since their alarm clocks wake them up they are awoken by their alarms soon after their biological clocks allow them to fall asleep. This disturbance of circadian rhythm causes lack of concentration and motivation, fatigue, and unhealthy eating habits to some extent. School administrators often claim that if their students slept earlier, they would be able to get up from a restful sleep in time for school. While early chronotypes can accommodate the early wake-up call, most adolescents have maturing circadian rhythms that shift their chronotypes later into the night. Studies show that delaying school start time by just one hour “enhance[s] students’ cognitive performance by improving their attention level, increasing rate of performance, as well as reducing their mistakes and impulsivity.” When these results were conveyed to school administrators, the biggest concerns they voiced were the complicated system and associated cost of bussing and coordinating this time with after-school activities.

We have rarely ever lived in synchrony with our biological clocks. Besides the jet lag felt by individuals traveling between time zones, social jet lag interferes with the biological clocks of sedentary individuals. Social jet lag is quantified as the difference between midsleep on free days and midsleep on work days, which can quickly accumulate for college students due to the late night skype sessions and the early morning sports practices. Another contributor to social jet lag is our generation’s dim exposure to day light due to long office hours complemented by the omnipresence of light at night with TV screens and computer monitors. It is no wonder that we are out of sync with the sun’s day-night cycle when we consider how much we expose ourselves to artificial light at times when the eyes expect darkness.

But how serious are the effects on our biological clocks? The circadian rhythm controls our complex biochemical processes through gene regulation. This biological clock creates cyclic physiological systems like core temperature, sleep cycle, and metabolite production, which change the way our body reacts to the environment. When we perturb our circadian rhythm, not only do we feel the sleep debt pull down on our eyelids, but also we put stress on our bodies’ natural functions, which in the long-term can lead to disease. In fact, the World Health Organization has recently classified “shift work that involves circadian disruption” as a potential cause of cancer: “Several decades of epidemiological research have clearly shown that shift workers develop more health problems than day workers. These include sleep problems, depression, cardiovascular pathologies, digestive tract issues, diabetes … and obesity … ”

The severity of these effects has prompted in depth research on the subject of circadian rhythms Dr. Erik Herzog and Dr. Paul Taghert of Washington University School of Medicine investigate how the disruption of the circadian rhythm is associated with mental illnesses, metabolic disorders, and problems in fertility by studying the molecular mechanisms and gene expressions that contribute to an individual’s circadian rhythm.

Compounding research shows that there are many different types of cells throughout the body that operate on a clock-like schedule. The biological clock is located in the suprachiasmatic nucleus in the brain. It receives light signals from the melanopsin photoreceptor, which is similar to the rods and cones in eyes.  If this area is lesioned, experiments involving rodents have shown a the failure to maintain a consistent sleep-wake, activity-rest schedule. The day-night environment is simulated by computerized chambers, and activity-rest schedules are represented by the rodents running on wheels. In a 1-credit seminar class called “Clocksclub”, Dr. Herzog and Dr. Taghert discuss these results and more in a forum for clocks researchers to share their lab experiences with their colleagues and interested undergraduate students.


Main Reference:
Roenneberg, Till. Internal Time: Chronotypes, Social Jet Lag, and Why You’re so Tired. Cambridge, Mass.: Harvard UP, 2012. Print.

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Neha Prasad is a junior from New Jersey. She can be reached at

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