On a typical day, we get up at about the same time in the morning and retire at about the same time every night.

That’s thanks to our internal circadian rhythm that controls our sleep wake cycle.

The system is regulated by the cells in the suprachiasmatic nucleus or SCN – located in the hypothalamus deep in the brain.

“The cells in the SCN generate their own near 24 hour rhythm,’ explains Dr. Benjamin Rusak, a professor of psychology and psychiatry at Dalhousie University in Halifax who has a special interest in sleep cycles.

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The SCN uses light and other external cues to control sleep – not how much you sleep or the quality of your sleep, but when you sleep, says Rusak.

The system works well when the internal cues are synchronized with the external environment “People who are typically day active do just fine; they wake in in the morning and they go to sleep at night and they sleep for the appropriate amount of time,” says Rusak.

But when those external cues are missing, things can get a bit out of whack. If you lived in a cave without daylight, your internal clock would gradually add a bit more time to your 24 hour rhythm – to the point where over the course of a month or so, you could be significantly out of synch, according to Dr. Rusak.

Melatonin, a natural hormone produced by the small pineal gland in the brain, helps to keep sleep and wake patterns on a 24 hour cycle.

Exposure to natural light instead of artificial light has a positive impact on the biological clock. Dr. Colleen Carney, Associate Professor, Department of Psychology, Ryerson University, Toronto, cites a study in which subjects were taken camping, where there was no intrusion of artificial light or sound. After being exposed to this natural setting for a week, the subjects’ circadian clocks shifted an average of about two hours earlier. Participants “naturally” awoke at dawn and fell asleep at dusk; but their total sleep time didn’t change. “They slept beautifully, like babies” even though the campground was actually quite noisy,” commented Carney.

This shift to an earlier cycle was correlated with the natural rise and fall of melatonin levels. Melatonin, a natural hormone produced by the small pineal gland in the brain, helps to keep sleep and wake patterns on a 24 hour cycle. Levels of melatonin normally begin to rise in the mid to late evening, remain high for most of the night, and then drop off in the early morning hours.

Light affects how much melatonin your body produces. During the shorter days of the winter months, your body may produce melatonin at different times of the day. Melatonin levels naturally slowly drop with age.

Moving from time zone to time zone may impact your circadian rhythm, too. “If you travel extensively, we recommend that you get as much light during the day of where you’re going and if can’t sleep at night to try to take melatonin before you go to bed to re-establish a normal sleep cycle.” says Dr. Atul Khullar, a psychiatrist, sleep specialist, and Medical Director, Northern Alberta Sleep Clinic (MedSleep Edmonton).

When the circadian rhythm is disrupted, any number of physical, emotional and mental problems can develop. Some people have what’s known as Circadian Rhythm Sleep Disorder – either an Advanced Phase or Delayed Phase type, depending on whether they’re an extreme morning lark who can’t stay awake after dinner but wakes up very early in the morning, or an extreme night owl, who finds it difficult to fall asleep before 3 am or so, says Dr. Maureen Ceresney, a sleep specialist at the University of British Columbia, Vancouver.

According to the American Academy of Sleep Medicine, another genetic circadian rhythm disorder is called ‘non-24 hour sleep phase disorder’ where sufferers sleep in 3-4 hour intervals during the day.

Circadian rhythm disorders are treated with medication, bright light therapy that uses artificial light to reinforce the internal clock, behavioural changes, and melatonin, which is available over the counter as a supplement.

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