The regularity of such journeys offers air crew no protection from the effects of jet lag, and can lead to decreased brain power and increased occurrence of major affective disorders.
Jim Waterhouse (Liverpool John Moores University, UK) and colleagues also looked at the effects of jet lag on athletes-finding impaired performance in training after crossing multiple time zones.
The symptoms of jet lag are diverse and are caused by inappropriate timing of the body clock in the new time zone. Sufferers report poor and interrupted sleep, early/delayed sleep depending on the direction of travel, mood changes, headaches, irritability and gastrointestinal difficulties. Flights east generally cause worse symptoms than those west. Sufferers of jetlag generally need a number of days to recover roughly equal to two thirds of the time zones crossed-with westbound flights, this number is half the time zones crossed.
The crossing of time zones disrupts the body's daily cycles (termed circadian rhythms). Sleep is badly affected because one such circadian rhythm-the body's core temperature-takes time to adjust. The hormone melatonin- usually secreted during sleep-is also implicated in jet lag symptoms. Journeys that cross three time zones or less are unlikely to cause jet lag. For journeys of over three time zones which will last less than three days, it is not worth adjusting the body clock.
For longer journeys (of over three time zones for more than three days), deliberately seeking or avoiding light at the new destination helps the body clock adjust, as does maintaining daytime alertness at the new destination by taking exercise and/or using regular stimulants such as caffeine. But they caution against the use of external melatonin until significant field studies have been completed
The authors conclude: "A more detailed understanding of the molecular changes associated with time zone changes is needed, with a view to developing drugs to promote clock adjustment, and further assessments of new sleep-promoting and alertness promoting drugs."
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Contact: Tom Reilly