Aircrew working on long-haul routes face serious health hazards from jetlag, experts have warned.

Pilots and cabin crew do not build up resistance to the effects of flying long distances, said scientists.

Menstrual irregularities were well-known in female crew members who made repeated long-haul flights, and mental effects had also been reported, said the discussion paper in The Lancet medical journal.
The authors, led by Professor Jim Waterhouse, from the Research Institute for Sport and Exercise Sciences at Liverpool John Moores University, wrote: "Deficits of cognitive performance and increases in psychotic and major affective disorders have also been described.

"Such effects have not been reported in healthy travellers whose experience of timezone transitions is far less extensive than those who regularly travel long distances."
Jetlag occurs when crossing timezones disrupts the body's daily cycles, which are set by a clock mechanism in the brain.

It is directly linked to the body's core temperature, which lowers during sleep and increases in the waking hours.

Longer trips can result in interrupted, early or delayed sleep, mood changes, headaches, irritability and upset stomachs.

Sufferers generally need a recovery time equal to two-thirds of the timezones crossed.

The scientists said it was wrong to assume that long-haul aircrew become immune to jetlag.

"Experience of timezone transitions does not act as a protection, although many aircrew members change their sleep behaviour to keep jetlag difficulties to a minimum," they wrote.

Deliberately seeking or avoiding light at the new destination can help the body adjust to a new timezone, said the authors. Maintaining daytime alertness on arrival by taking exercise or drinking coffee could also help.