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Jet lag

NHS Direct Online Health Encyclopaedia

The world is divided into 24 time zones. The Greenwich meridian in London is the base. The time changes by one hour for every 15 degrees travelled in either direction from the Greenwich meridian.

Jet lag happens when you cross over a number of time zones and disrupt the bodys normal 'circadian' rhythms or 'biological clock'.

Your internal body clock controls when you are sleepy and when you are alert, as well as hunger, digestion, bowel habits, urine production, body temperature, secretion of hormones and blood pressure. This biological clock is normally synchronised with your local time so that you feel hungry in the morning and sleepy in the evening.

When you travel across time zones, the body needs time to adjust.

Symptoms of jet lag vary from person to person and depend on the distance travelled and number of time zones crossed.

Symptoms may include:

Disturbed sleep patterns; sleepy during the day, but not able to sleep at night;
Disrupted digestion and bowel habits;
Feeling disorientated and/or clumsy;
Loss of appetite;
Lack of concentration/feeling less alert;
Memory problems;
Cold or flu-like symptoms;
Feeling weak and light-headed; and
Lack of energy.
It takes about one day to recover for each time zone you cross and can take up to a week to fully adjust. You can also suffer jet lag on the return journey, but to a different degree depending on the direction of travel.

When you cross time zones, you arrive hours ahead or behind the time in the country you fly from. The body has to adjust to new times of light, darkness and meals and often to differences in temperature.

The problem is worse when travelling east because the body is better able to adapt to a slightly longer day than a slightly shorter one. So, your body adapts better when travelling west because you are extending your day, rather than travelling east, when you are shortening it. In other words, it is easier to delay sleep for a few hours than force yourself to sleep when you are not ready.

The effects of jet lag can be intensified by dehydration, tiredness, lack of sleep, lack of oxygen in the aeroplane cabin, alcohol and stress. Those people who have a very strict routine tend to suffer most from jet lag. This is why children and babies, who can sleep almost anytime, rarely show symptoms of jet lag.

People who have to take medication at certain times of the day should seek medical advice before travelling.
It takes about one day to recover for each time zone you cross. There are various methods that may help you avoid jet lag or reduce its effects. Different people will prefer different methods.

Before the flight:

Try to get plenty of sleep in the days before you travel. A few days before you travel, you could start going to bed and getting up earlier (if travelling east) or later (if travelling west). If you book a flight that arrives late afternoon/early evening you can get some natural light and this will help regulate your body clock.

On the flight:

Adapt to local time as soon as you get on the flight by changing your watch (for short trips stay on your home time instead of adjusting your watch).
Take things easy in the first few days- dont schedule any important meetings.
If possible, break up long journeys with a stopover.
Avoid overeating and drinking alcohol on the flight.
Eat at the same meal times as your destination.
Drink plenty of water on the flight (and before and after).
Try and do some light exercise on your flight and during your trip.
Try to sleep or nap on the plane. This is especially important if it is going to be daytime when you arrive at your destination. Some people use sleeping tablets, but most last for eight hours and this means you wont be able to move around during the journey (See DVT).
When you arrive:

Get into a routine immediately.
Allow yourself time to adjust when you arrive dont schedule any important meetings for the first day.
Get some exercise every day.
Drink caffeine only at the times when you most need to be alert. This is often not first thing in the morning, but at around 3pm in the afternoon.
Drink plenty of fluids.
Take oral re-hydration sachets to ease dehydration.

Avoid sleeping until bedtime; do not nap during the day, as it will not help you adjust to the local time. Do not drink caffeine or alcohol or smoke three hours before you go to sleep, as they are stimulants. Do not eat a heavy meal before going to sleep (but do not go to bed hungry). A relaxing bath can help you feel sleepy before bed and the background sound of a fan or radio may help you sleep. Remember that sleeping tablets, which are only available on prescription, may make you drowsy the next day.

Try to get some natural light when you arrive if possible, as it will regulate or advance the biological clock. If you are travelling east, expose yourself to morning light and you should be able to go to sleep earlier. If you are travelling west, expose yourself to afternoon light and you should be able to go to sleep later (1).


Eat your meals at the correct times for the new time zone. Have meals containing protein for breakfast and lunch to keep you alert and have a meal containing carbohydrates for dinner to help you sleep.


Melatonin is a hormone that is naturally secreted in the evening from the pineal gland in the brain and tells the brain it is time to sleep. Melatonin has been used in experiments to prevent jet lag, but most evidence is inconclusive. It is unlicensed in the UK and not recommended for use as little is known of its long-term effects.

1. Manchester Online
© Queen's Printer and Controller of HMSO, 2005

Crown copyright material is reproduced with the permission of the controller of HMSO and the Queens Printer for Scotland.



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