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Your body's circadian clock

The secret of your unique sleep needs can be revealed by considering your body’s internal clock, also called the circadian clock (circadian comes from a Latin word meaning ‘‘around the day’’). It refers to the body’s response to external things – sunlight, for example – during a 24-hour cycle.

Your body's internal 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 the US 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 Europe, for example) also causes jet lag but not to the same degree.

Perils of shift-work

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 many of the motor vehicle accidents on long stretches of road 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.

(Elise-Marie Tancred and the Health24 team)

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