Aircrew who endure jet lag repeatedly can suffer problems with menstrual cycles, a reduction of brain power and transient psychotic disorders, according to a review.

Passengers who cross time zones less frequently are less likely to have serious problems, but they usually suffer sleep disturbance and changes in body function, a team from the Research Institute for Sport and Exercise Sciences at John Moores University in Liverpool say in The Lancet. Athletes often find that their performance is reduced after crossing multiple time zones.

There are many symptoms of jet lag, which vary between individuals and depend on the number of time zones crossed. These are caused because the natural rhythms of the body clock are no longer in time with the new time zone.

Sufferers reported poor and interrupted sleep, early or delayed sleep depending on the direction of travel, mood changes, headaches, irritability and gastrointestinal difficulties.

For most people, journeys that cross three times zones or fewer are unlikely to cause jet lag. Some people are more sensitive and may even be upset by the resetting of the clock to summer and winter time, a difference of only an hour.

The team gives a simple calculation of how long it takes to recover. When going east to west, they say that the recovery time is half a day for every time zone crossed.

On journeys from west to east, which have worse effects generally, the team recommends two thirds of a day for every time zone crossed. They say that it is not worth adjusting the body clock for trips of three days or fewer.

Adjustment of the body clock is helped by deliberately seeking or avoiding light at the new destination. It is also helpful to maintain daytime alertness at the new destination by taking exercise and/or using stimulants such as caffeine.

Some doctors have claimed that the use of melatonin, a hormone secreted during sleep, can reduce the symptoms. The team, led by Jim Waterhouse, cautioned against the use of melatonin until significant studies had been completed.

Now adjust your body clock

— Try to adjust the body clock by controlling exposure to light. After flights to the west with a five-hour time difference, for example, avoid bright light between midnight and 6am, and seek it out between 4pm and 10pm

— After flights to the east with a five-hour time difference, avoid bright light between 2am and 8am. Wear dark glasses, get indoors as soon as possible and dim the lights. Seek out bright light between 10am and 4pm

— Avoid sleeping on board unless it is night time at your destination

— Keep alert by day by using a harmless stimulant such as coffee. Sightseeing in bright sunlight or playing tennis or golf is an alternative

— On short trips of three days or fewer, stay on home time and try to organise sleep and engagements to fit in

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