International travel and health

Jet lag

Jet lag is the term used for the symptoms caused by the disruption of the body’s “internal clock” and the approximate 24-h (circadian) rhythms it controls. Disruption occurs when crossing multiple time zones, i.e. when flying east to west or west to east. Jet lag may lead to indigestion and disturbance of bowel function, general malaise, daytime sleepiness, difficulty in sleeping at night, and reduced physical and mental performance. Its effects are often combined with tiredness caused by the journey itself. Jet lag symptoms gradually wear off as the body adapts to the new time zone.

Jet lag cannot be prevented but there are ways of reducing its effects (see below). Travellers who take medication according to a strict timetable (e.g. insulin, oral contraceptives) should seek medical advice from their doctor or a travel medicine clinic before their journey.

General measures to reduce the effects of jet lag

  • Be as well rested as possible before departure, and use any opportunity to rest during medium to long-haul flights. Even short naps (less than 40 min) can be helpful.
  • Eat light meals and limit consumption of alcohol. Alcohol increases urine output, with the result that sleep may be disturbed by the need to urinate. While it can accelerate the onset of sleep, alcohol impairs the quality of sleep, making it less restful. The after-effects of excessive consumption of alcohol (“hangover”) can exacerbate the effects of jet lag and travel fatigue. Alcohol should therefore be consumed in moderation, if at all, before and during the flight. Caffeine should be limited to normal amounts and avoided within 4–6 h of an expected period of sleep. If coffee is drunk during the daytime, small amounts every 2 h or so are preferable to a single large cup.
  • At destination, try to create the right conditions when preparing for sleep and get as much sleep in as normal in the 24 h after arrival. A minimum block of 4 h sleep during the local night – known as “anchor sleep” – is thought to be necessary to allow the body’s internal clock to adapt to the new time zone. If possible, make up the total sleep time by taking naps during the day in response to feelings of sleepiness. When taking a nap during the day, eyeshades and earplugs may help. Exercise during the day may help to promote a good night’s sleep, but avoid strenuous exercise within 2 h of trying to sleep.
  • The cycle of light and dark is one of the most important factors in setting the body’s internal clock. A well-timed exposure to daylight, preferably bright sunlight, at the destination will usually help adaptation. When flying west, exposure to daylight in the evening and avoidance in the morning (e.g. by using eye shades or dark glasses) may be helpful; flying east, exposure to light in the morning and avoidance in the evening are to be recommended.
  • Short-acting sleeping pills may be helpful. They should be used only in accordance with medical advice and should not normally be taken during the flight, as they may increase immobility and therefore the risk of developing DVT.
  • Melatonin is available in some countries. It is normally sold as a food supplement and therefore is not subject to the same strict control as medications (for example, it has not been approved for use as a medication in the United States, but can be sold as a food supplement). The timing and effective dosage of melatonin have not been fully evaluated and its side-effects, particularly in long-term use, are unknown. Moreover, manufacturing methods are not standardized: the dose per tablet can vary considerably and some harmful compounds may be present. For these reasons, melatonin cannot be recommended.
  • Trying to adjust to local time for short trips of up to 2–3 days may not be the best coping strategy, because the body clock may not have an opportunity to synchronize to the new time zone, and re-synchronization to the home time zone may be delayed after the return flight. If in doubt, seek specialist travel medicine advice.
  • Individuals react in different ways to time zone changes. Frequent flyers should learn how their own bodies respond and adopt habits accordingly. Advice from a travel medicine clinic may help in formulating an effective coping strategy.