Sleep Disorders

Updated 23 May 2013

Your body's internal clock

The secret of your unique sleep needs can be revealed by considering your body’s internal clock, also called the circadian clock.


Your circadian clock is in the hypothalamus. It’s a structure the size of a pinhead; it responds to light received by the eye and regulates the secretion of melatonin, the sleep hormone.

In all people, with the exception of teenagers, the amount of melatonin secreted increases from sunset onwards – it’s literally the body’s Mr Sandman.

This part of the brain also synchronises other functions linked to going to sleep and waking up, including body temperature, hormone secretion, urination and blood pressure.

What causes jet lag?
If you visit someone in Australia you fly from west to east and cross several time zones. This interferes with your circadian rhythms in the worst possible way and results in jet lag. Crossing time zones in the other direction – from east to west (from Australia to South Africa, for example) also causes jet lag but not to the same degree.

Today artificial melatonin supplements and light therapy (doctors apply bright lights during sleep to restore normal biorhythms) are used to combat the effects of jet lag. Melatonin should however be used only under medical supervision. It builds up in the body and its side-effects haven’t yet been thoroughly researched.

Perils of shift-work
Jan Top of the Panorama Sleep Clinic says shift workers suffer from a similar type of exhaustion because their bodies’ normal exposure to light is disturbed. Fatigue among shift workers has resulted in serious industrial disasters.

The nuclear accidents at Chernobyl and Three Mile Island, the Exxon oil spill and most of the motor vehicle accidents on the road between Laingsburg and Beaufort West have been linked to sleep deprivation. Shifts should be limited to eight hours and the body must be allowed a rest period before shifts change, Top says.

(This is an edited version of a story that originally appeared in YOU Pulse / Huisgenoot-POLS magazine)


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Sleep disorders expert

Dr Alison Bentley is a general practitioner who has consulted in sleep medicine and sleep disorders, in both adults and children of all ages, for almost 30 years. She also researches and publishes on a number of sleep-related topics both in formal research journals and lay publications including as editor of Sleep Matters, an educational newsletter on sleep disorders for doctors.

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