Clock change will hit early risers hardest says St Thomas' sleep expert

So-called 'larks' who are naturally awake and alert in the morning will suffer most as they are more sensitive to the light and are therefore worst affected by the change in the time the sun rises.

Although environmental factors like light and noise obviously contribute to our ability to sleep at any particular time of day, a study by Dr Williams and his colleagues in 2003 found that our predisposition to being alert and awake in the morning or in the evening is also determined by our genes.

Their study found that a number of genes govern sleep and our body clocks and therefore influence when we are naturally at our most alert. This means that whether you are a 'lark' or an 'owl' can be largely hereditary and there is little you can do to change it.

Dr Williams who runs the sleep centre at St Thomas', said: "If you are a lark there is a good chance that you will worst affected by the clock change but almost everyone might feel some effect of losing an hour of sleep.

"We are generally a sleep deprived society and most people sleep, on average, for an extra two hours over the weekend to make up for the sleep they have missed during the week.

For those who have difficulties adjusting their sleep pattern to account for the clock change, Dr Williams has some advice:

• Relax before bedtime and try not to worry about sleeping;
• Don't drink caffeine or alcohol before bed;
• Try not to nap in the afternoon;
• Take regular exercise but make sure that you are finished three hours before bedtime;
• Try to keep a regular sleeping pattern;
• If light or noise affects your sleep try wearing an eye mask or ear plugs.