Text 6. Body Clock

A circadian rhythm is an approximate daily periodicity, a roughly-24-hour cycle in the biochemical, physiological or behavioural processes of living beings, including plants, animals and fungi. The 'body clock' is the result of the Circadian Rhythm, which is the cycle of night and day in a 24 hour period.

The circadian rhythm also affects body temperature, blood pressure, digestive secretions and hormone production.

Circadian clocks regulate the daily fluctuations of many physiological and behavioural aspects in life, and are synchronised with our surrounding environment via light or temperature cycles. Natural changes in the length of the day mean that an animal's circadian clock often has to reset itself on a molecular level, to avoid getting out of sync with the changing calendar.

By following a carefully timed program of light and dark at the times your body clock is most responsive, you can quickly reset it to the new time zone. Instead of taking a week or more to adjust to an intercontinental journey, you can become fully adapted to the new time zone in just one or two days.A successful time zone shift depends on knowing the exact times to seek and avoid bright light. Exposure to light at the wrong time can actually make jetlag worse.

The proper schedule for light exposure depends a great deal on specific travel plans. Taking a night flight to Tokyo, for instance, creates very different demands than a day flight to Los Angeles. Personal variables are important too; if you're a 'night owl' you'll typically need a different schedule to a 'lark'What makes some of us "night owls "people who don't go to bed until 2 a.m. (or even later) while others are "larks" early birds who wake up bright-eyed and ready to go at the crack of dawn? The answer lies mostly in our internal body clock, which is largely determined by our genes. In addition to driving our 24-hour (or circadian) sleep-wake cycle, this clock regulates hormone levels, body temperature, blood pressure, alertness and performance ability.

The cycles themselves are controlled mainly by a region within the brain's hypothalamus known as the suprachiasmatic nucleus. This area responds to signals from the retina, specifically, the light that travels from our eyes to our brain, which is the most important factor in orienting our bodies to daytime alertness and night-time sleep.

Why do we wake up in the morning and go to sleep at night? Why do we feel hungry at certain times of the day? The reason is that we all have a body clock and it works like this. Your brain produces hormones like melatonin and adrenalin which make your body temperature rise and fall. When it falls you feel sleepy, when it rises you wake up. The body clock controls the production of these hormones, so that you wake up and feel sleepy at different times of the day. Here is a typical day in the life of your body.

7 am: When the sun comes up, light hits your eyelids and your brain switches off the sleep hormone, melatonin. Your temperature rises and you wake up. This is a good time to go jogging. Exercise produces adrenalin, which will make you more alert through the day.

8 am: Breakfast is the most important meal of the day. It gives you energy for the morning. However, you . shouldn't eat too much carbohydrate at this time. It's converted into energy very quickly, so you feel hungry again about an hour later. It's better to eat a more balanced meal with some protein, fibre, and a little carbohydrate.

9 - 11 am: Your mind is most alert in the morning because you have a lot of energy and your stress level is low. This is the best time for mental work.

11 am: Your brain has used about 20 per cent of your body's energy by now, so it's time for a snack. Good snacks for energy are nuts and fruit, such as apples and bananas.

Noon: Your temperature starts to fall and your stress level is rising. You should go for a walk or talk to a friend now. This will make you feel brighter and happier.

1 pm: This is the best time for lunch because your energy level is low.

2 pm: You feel sleepy because your brain naturally produces melatonin.

3 pm: Your temperature is rising again. Your body needs sugar for energy. Have a snack such as chocolate or a banana. It's better to eat a few snacks through the day rather than just two or three big meals. From now till six o'clock your memory is at its best, so this is a good time for learning.

6 pm: Your temperature is at its highest. If you want to do some heavy exercise, like weightlifting or aerobics, you should do it now because your energy level is high. Stress levels are high, too, and exercise helps to reduce stress.

7.30 pm: The best time to eat dinner is between seven and eight o'clock. However, you should always eat an evening meal at least two hours before you go to bed.

9 pm: Your temperature starts to fall again. Many people worry or feel depressed now because they think about the things that they have to do the following day.

10 pm: When it gets dark, your brain starts to produce the sleep hormone, melatonin. You feel tired and your body gets ready to go to sleep.