Lewis Wolpert: 'Biological clocks are found throughout all living organisms'

I have always been puzzled by what determines how much sleep we need. I have always slept a lot and believed I needed to, and I also suffer badly with jet lag. It is now clear that time is embedded in our genes, and that biological clocks are found throughout all living organisms - from bacteria through worms to humans. We live in a world of day and night and have had to adapt. As a result, we spend an average of 20 years of our lives sleeping.

I have always been puzzled by what determines how much sleep we need. I have always slept a lot and believed I needed to, and I also suffer badly with jet lag. It is now clear that time is embedded in our genes, and that biological clocks are found throughout all living organisms - from bacteria through worms to humans. We live in a world of day and night and have had to adapt. As a result, we spend an average of 20 years of our lives sleeping.

At a large international meeting of neuroscientists, much of the discussion over coffee was whether those who were in a very different time zone to home could get over their jet lag by taking melatonin. There are recent studies suggesting that it can help. Melatonin is secreted by the pineal gland in the brain during darkness, and it sets the master body clock that we all have. This gland is located in a special part of the brain and controls our circadian - daily - rhythm.

This clock region has some 50,000 nerve cells and their genes are turned on and off in a complex manner to measure the passage of time. This clock can also control body temperature, which is at its highest at night and one degree lower after a good sleep.

While our clocks all run on a 24-hour cycle, they can affect our behaviour in quite different ways. Some of us - not me - are alert early in the morning, while others are best at night and go to bed very late. The historian Roy Porter wrote more than 100 books in his life. When I asked him how he did it, he told me that he got up very early each morning and was at work by 5am.

When I asked how long he continued he was puzzled by the question - clearly most of the day. Had his genes combined to give him a special clock?

The elderly, it has been found, produce less melatonin and so experience more disturbed sleep. But if they are exposed to bright light during the middle of the day, their melatonin production is higher at night and they sleep much better.

A serious age-related sleep problem occurs with Alzheimer's disease, as some nerve cells are lost from the master clock. As a result, the night /day cycle of sufferers may be out of synch with the true day and night by several hours. This can make those with Alzheimer's active when their carers want to sleep. Again, exposure to bright light during the day can help alleviate these symptoms.

Patients with seasonal affective disorder - winter blues - also have disturbed sleep patterns, and this condition can be treated with light. Many people have jobs that go against their natural biological clock, night shift workers being the obvious example. Their sleep can be seriously affected.

These issues and biological clocks in general are well described in a new book, Rhythms of Life, by Russell Foster and Leon Kreitzman. One of their most interesting conclusions is that doctors in general have ignored the typical times that particular illnesses occur, and thus do not pay attention to the best time at which medication should be given.

The greatest prevalence of asthmatic symptoms occurs around four in the morning and this is the best time to take medication. The risk of heart attacks and strokes is nearly 40 per cent higher between six in the morning and noon. Since such illnesses are associated with high blood pressure, it seems to make sense to take medication to reduce it in the morning.

Another example is provided by arthritis. Rheumatoid arthritis is characterised by stiffness in the morning, whereas the symptoms of osteoarthritis are worse in afternoon and evening. This difference in timing should probably determine when the appropriate medicine should be taken. And there is emerging evidence that taking anti-cancer drugs at different times of the day can have a dramatic impact on the success of particular treatments.

It is a bit disconcerting, too, to learn that death is most likely to occur between eight and ten in the morning.

Lewis Wolpert is professor of biology as applied to medicine at University College, London