What is the internal body clock?
Your body clock is what enables you to synchronise the working of your body with the day and night. 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 resets it slightly every day.
Your body clock and hormones
When allowed to run naturally your body clock operates on a cycle of just over 24 hours. It controls everything from the time it is easiest to exercise (early evening) to the time you are most like to have a heart attack (in the morning) or stroke (between 6 am and 8 am or 6 pm and 8 pm).
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 produced by the adrenal glands, and melatonin, a hormone secreted during darkness by the pineal gland in the brain, which helps regulate sleep cycles.
You can reset your body clock
'It is possible to schedule certain tasks to coincide with peak performance in a particular area,' says Dr Derk-Jan Dijk, Professor of Sleep and Physiology and co-director of the Centre for Chronobiology at Surrey University, an expert on the sleep patterns of older people. We can also control our circadian or daily rhythms to a degree through sleep, melatonin and light.
Take a nap
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 sleep in, especially at the weekends, and this can result in sleep debt. Napping is the best way round this.
'An early afternoon nap at the weekend, can help to redress sleep imbalance,' says Professor Dijk. However he cautions, 'Don't nap for too long, as this can stop you getting to sleep at a normal time that night.'
Melatonin as a regulator
Melatonin acts as a regulating switch, pushing the body clock forwards or backwards. Melatonin production falls as we get older, which may explain why younger people find it easier to drop off and to sleep longer without interruption.
It's been suggested that melatonin supplements (not available in the UK because of safety concerns although you can get them on the Internet) could help treat insomnia as well as jet lag and sleep problems experienced by shift workers.
Beat jet lag symptoms
Experts are still divided on its usefulness, however. According to one British expert, eight out of 10 studies show that melatonin helps jet lag. US research published in May 2006, meanwhile, suggests that supplements are only effective in encouraging sleep during daylight, when the body is not producing its own melatonin. At night when melatonin is being secreted, taking a supplement appears no better than placebo. Short-term melatonin appears to be safe. However it should not be taken by people taking warfarin or with epilepsy. Consult your doctor before taking it.
Your circadian rhythm
Bright light can help reset your circadian rhythms, according to Professor Dijk. ‘If you find your body clock is out of sync – as a result of jet lag, for example – light can help to realign your body's circadian rhythm with the new time zone.'