Your Body Clock - The Rhythm of Life

Your body clock governs and synchronises your natural pattern of physical and behavioural processes, such as sleep and wake cycles, body temperature, blood pressure and the release of hormones. They are timed roughly to a 24 hour period, although without naturally occurring light signals, we would probably operate nearer to a 25 hour schedule.

We all have a timing mechanism, or 'clock,' that controls periods of activity and inactivity. These clocks are known as circadian rhythms - circadian comes from the Latin circa meaning about, and dia meaning day. You’ve probably noticed that you sometimes feel more energetic and alert during certain periods of the day, and more lethargic and run-down at other times of the day. While many people refer to circadian rhythms as a single process, there are actually a number of body clocks that fluctuate throughout the day. For example, mental alertness tends to peak twice in a day at around 11am and 8pm, while physical strength tends to be at its height at around 10am and 5pm.

The actual 'clock' is a cluster of around 10,000 nerve cells that lie buried deep within part of the brain called the hypothalamus. Light coming in through our eyes 'trains' the body clock to keep in time with day or night, and even resets it slightly each day.

One of the most important ways in which the body clock works is by triggering the production of hormones, such as the stress hormones, adrenalin and cortisol, which are produced by the adrenal glands. And melatonin, a hormone secreted during darkness by the pineal gland in the brain, helps to regulate sleep cycles.

As we get older sleep tends to be more easily disrupted by external influences, such as light and sound, and internal ones such as stress and anxiety. We also become less able to have a lie-in, especially at the weekends. For most people, studies show that the pressure to sleep builds up throughout the day and peaks around 9pm-10pm. At this time, the body's temperature starts to drop and then lowers approximately one degree during sleep. As it starts to rise again, around 4am, the process of waking begins.

Melatonin acts as a regulating switch, adjusting the body clock forwards or backwards. The pineal gland, located deep within the brain, produces and secretes the chemical melatonin at high levels during the night. A number of factors can affect melatonin secretion, especially light and many common medications. For example, a lamp turned off at bedtime causes the stimulation of the pineal gland, and sunrise triggers the chemical process that enables a person to begin waking up.

Bright light can help reset your circadian rhythms. If your body clock is out of sync, perhaps as a result of jet lag, light can help to realign your body's circadian rhythm with the new time zone.

Fortunately we don't suffer permanent jetlag when we go abroad because the body clock resets itself when our eyes are exposed to light. A small number of nerve fibres in the retina feed in to the body clock and adjusts the rhythm, according to whether it is light or dark. This system allows the clock to adapt to changes in day length and the demands of every-day living. But the system is not perfect and does not kick in immediately, which is why we feel jet-lagged after a long haul flight, or especially tired after working a night-shift.

Now check out our hour-by-hour guide to see how you can get the best out of your day by pinpointing the optimum times for working up a sweat, enjoying a glass of wine, using some serious brainpower - or even making love!

MIDNIGHT - 1.00am
If you're pregnant and near your due date, this is the time you are most likely to go into labour as the hormone that starts the process, progesterone, is at its highest level.

2.00 - 3.00am
Time of deepest sleep.

4.00 - 5.00am
Lowest body temperature.

There is a rise in blood pressure at this time, and melatonin secretion stops. Levels of cortisol, a hormone related to stress but which can help mind function, rise rapidly between 6am and 8am as the body prepares for the day ahead.

The levels of hormones which stimulate sex drive - testosterone (in men and women) and progesterone and oestrogen (in women) - are up to five times higher at this time of day. Good time to try for a baby!

The ideal time to weigh yourself is before breakfast, without clothes and after the toilet (bowel movements are most likely to occur now). Weight fluctuates at period time and during the day when you take on food and fluids. Ideally weigh yourself just once a week, at the same time.   

This is the best time to have breakfast as your digestive system is at its most efficient, and any fats absorbed from food are less likely to be deposited in your body.

10.00 - 11.00am
Heart rate and blood pressure have ‘warmed up’. Your mind is at its sharpest. Concentration levels, short-term memory and logical reasoning are at their best. This is the right time to make decisions or to sit an exam.

NOON - 1.00pm
Mental slump time! Take time to sit down and enjoy lunch. A walk in fresh air may help to feel more energised. And a daily dose of vitamin D from sunlight, especially during the winter months, is essential for healthy bones and a strong immune system.

2.00 - 3.00pm
That mid-afternoon drowsy feeling is likely to hit around now as your lunch is digested and energy levels drop. An afternoon nap would be very welcome now, but obviously not if you are working or have children to look after!

4.00 - 5.00pm
Adrenaline levels are at their highest, so an ideal time for exercise. Also your lungs are working at maximum efficiency and muscles are at their warmest and most flexible. Hand-eye co-ordination is good, so great time for playing sports.

6.00 - 8.00pm
Eat your evening meal as your body is the most relaxed, and smell and taste are at their peak so you'll enjoy your meal more. Your liver is at its most active in detoxifying the body and the digestive system is at full capacity, so now is the time to enjoy a glass of wine over dinner. Your stomach produces more acid in the early evening, so this is when you are most likely to suffer indigestion.

9.00 - 10.00pm
Metabolism is now slowing down, which means less energy is burned. Be aware that eating high calorie food now is more likely to be stored as excess body fat.

10.00 - 11.00pm
Libido is at its highest point, so ideal time to make love. Also, ovulation is most likely in women at this time, so chances of conception are high.