When the clocks go back: reset your body clock in a few days.

When the clocks go back, the time changes overnight but your body clock, your circadian rhythm, takes longer. Sleep, appetite and mood can feel it for up to three weeks. Three signals on the new time shorten that: light, meals and movement.

This year it's Sunday 25 October: an extra hour in bed, on paper. Then on Monday you're awake at five, starving by half eleven, and it's dark when you leave the office. People I work with tell me the same every October: "I wake before the alarm and can't get back to sleep."

What happens to your body when the clocks go back?

It usually throws sleep, appetite and mood off schedule. For a few days your body stays on the old time: your six is its seven.

• Early waking. Awake an hour early, and flagging on the sofa by nine.
• Hunger at odd times. Your stomach wants lunch at half eleven and dinner at six.
• A slower head. Tiredness, irritability, poor focus.

How long does it take to adjust to the clock change?

Up to three weeks. As you get older, usually longer.

October is the easy direction. It's like flying one time zone west: your day gets longer and your body clock only has to run late, which it finds easier than running early. That's why March, losing an hour, hits harder.

You have more than one clock. The one in your brain is set mainly by light. Your liver, muscles and fat have their own, and mealtimes help set them. If light and dinner tell different times, they drift out of step.

One hour matters to your heart, too. In countries that change the clocks, heart attacks rose by about a quarter the day after the spring change and fell by about a fifth after the autumn one. Road accidents showed the same pattern.

How do you adjust to the clock change quickly?

Give your body the new time's signals from day one, and keep the same alarm at weekends. Regular hours usually mean deeper sleep.

Morning light first. Every day, in October as in March, ten minutes outdoors within an hour of waking, without sunglasses: that's the signal that resets your clock. Daylight later helps too: a 10 to 15 minute walk outside after lunch gives you daylight and better digestion. Now it's dark by five, that counts even more: the serotonin you make in daylight becomes melatonin in the dark.

Meals on the new time, from the first. Lunch at half twelve, even if you're hungry at half eleven. A savoury breakfast helps: eggs, Greek yoghurt or nuts.

Move by day. Train in the morning or afternoon. Hard exercise close to bedtime can keep your brain switched on.

In the evening, your usual bedtime. The commonest October mistake is giving in to early sleepiness: bed at nine, wide awake at five, body clock stuck on the old time. Dim lights, a book, screens off an hour before sleep, and bed at your normal time.

A week of clear signals usually makes the new time yours. For long-haul flights, see the article on jet lag.