We all have an internal body clock (sometimes referred to as our circadian rhythm), which controls when we feel sleepy and when we feel active. The clock is governed by daylight – so we get used to a regular rhythm of daylight and darkness. Travelling to a different time zone means that your body clock will be out of sync with local time, and you may end up feeling sleepy during the day and unable to sleep at night.
The world is divided into 24 time zones, with each one an hour different from the next. All the time zones are measured from a reference point known as the Greenwich Meridian in London, UK. The time changes by one hour for every 15 degrees travelled in either direction from the Meridian.
You can get symptoms of jet lag if you cross three or more time zones. This means that if you fly from the UK to Europe, Africa or the Middle East you probably won't be as affected. But most people will have some symptoms travelling from the UK to Asia, Australasia, the Pacific islands, the USA and Canada or Central and South America.
Jet lag tends to be more of a problem if you're flying east because your body finds it harder to adjust to a shorter day than a longer one.
The symptoms of jet lag are different for everyone, and also depend on how many time zones you have crossed and in which direction you have travelled.
Usually it makes you feel tired and low in energy during the day. It disturbs your sleep, so you may have trouble getting off to sleep, or wake up often at night or early in the morning. You might have difficulty concentrating, and be a bit clumsy or irritable because you’re so tired.
You may also have other symptoms, such as indigestion, altered bowel habits and a low appetite. You may also feel generally unwell.
How severe, and how long your symptoms last for, will generally depend on the number of time zones you cross in your flight. You may start to feel better in a couple of days, but if you have travelled a very long distance it can take up to 14 days to feel better.
Different body rhythms adjust at different rates. So, for example, you might feel your digestion has recovered but still have trouble sleeping.
There are a few things that can make jet lag worse. These include the following.
- Tiredness – be as well rested before your flight as you can, and rest during the flight.
- Alcohol – although it may help you nod off, alcohol impairs the quality of sleep and having a hangover can make jet lag feel worse, so if you drink any alcohol before or during your flight, make sure it’s just a small amount.
- Caffeine – this can disrupt sleep too. Stick to the amounts you normally drink and don’t drink caffeine within a few hours of when you plan to go to sleep.
Help your body clock adjust
If you’re staying at your destination for more than two or three days, it’s worth trying to help your body adjust to the new time zone. It may help to begin shifting your internal clock before you leave – try getting up and going to bed slightly earlier if you're flying east, or getting up and going to bed later if you're flying west.
As soon as you board your flight, adjust your watch to the destination time. If you arrive in the evening, try not to sleep too much on the plane so that you can go to bed when you arrive. And sleep as much as you can if your flight arrives in the morning, so you can stay awake through the day.
When you arrive, try to get into the local routine immediately and spend the day outdoors, because natural light can help your body clock adjust. If you travelled west, try to get more morning light after you arrive and avoid it in the afternoon. If you went east, seek afternoon light and avoid morning light. Avoid exposure to bright sunlight – use sunglasses, eye masks and blackout curtains to help keep light out.
If you're travelling on business, it may be helpful to arrange important meetings to coincide with daytime in your home country.
If you’re only staying a couple of days, your body may not have time to adjust to local time. Sometimes it’s best to just to stick to your usual (home) timings. If you’re not sure, make an appointment at a travel clinic to see a travel medicine expert.
There aren’t any medicines specifically available for jet lag. However, there’s evidence to suggest that the hormone melatonin can be useful in people who are travelling across more than five time zones. Melatonin has not been licensed yet for jet lag, but if a doctor who specialises in travel has experience in this area, he or she may be able to prescribe it to you as an off-licence medication. Talk to a doctor at a travel clinic if you’re travelling somewhere where you think you will need this treatment.
If you’re tired when you need to be alert, caffeine can help as a temporary pick-up. But don’t drink lots of coffee in the hours before you need to get to sleep.
It you know you have trouble with sleeping when you have jet lag, talk to a specialist at a travel clinic before you go. He or she might suggest taking sleeping tablets for a couple of days, until your body clock adjusts. It’s best not to take these on the flight because they may keep you still in your seat for too long and increase your risk of deep vein thrombosis (DVT). Also, they can mix badly with alcohol to make you even sleepier.
For more information on how to cope with jet lag, seek advice from a travel clinic.
- National Travel Health Network and Centre
- Normal sleep, sleep physiology, and sleep deprivation. eMedicine. www.emedicine.medscape.com, published 5 December 2011
- Ker K, Edwards PJ, Felix LM, et al. Caffeine for the prevention of injuries and errors in shift workers. Cochrane Database of Systematic Reviews 2010, Issue 5. doi: 10.1002/14651858.CD008508
- Sleeplessness and circadian rhythm disorder. eMedicine. www.emedicine.medscape.com, published 7 June 2012
- Sleep disorders – shift work and jet lag. Prodigy. www.prodigy.clarity.co.uk, published July 2009
- International travel and health. World Health Organization. www.who.int, published 2012
- Jet lag: rapid time-zone change syndrome. World Health Organization. www.searo.who.int, published 19 August 2011
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- National Travel Health Network and Centre
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