Each year, thousands of people experience problems concentrating, loss of appetite, indigestion and disrupted sleep patterns for several days after they have flown across different time zones for their annual holiday or on business.
Research, published today in the Journal of the Royal Society of Medicine, shows how people can minimise jet lag by understanding how their bodies respond to light at different times.
Dr Jim Waterhouse, from the Research Institute for Sport and Exercise Sciences at Liverpool John Moores University, has worked out methods of avoiding jet lag without taking any drugs to induce sleep.
"The most effective way to avoid jet lag is to understand the way light affects the body clock," he said.
A pair of receptors inside the brain regulates the human body clock, which controls when to wake up and when to fall asleep. Travelling to another time zone, or doing shift work, can throw these receptors out of phase with daylight hours and there is a delay as they try to adjust. Scientists believe that it is the retina at the back of the eye or possibly the skin that senses the light and sends the information to the brain.
Although some researchers have had success adjusting the body clock with melatonin, a hormone that can advance or delay clock phases, this is not an option for many people as it is banned in Britain.
Dr Waterhouse said body temperature drops at around 4am. "If there is a light pulse in the following six hours, the body clock advances by a few hours. If the pulse takes place in the six hours before 4am there is delay," he said. "Light at other times has no effect."
Going east, it is harder to adjust to local time than when going west and the traveller who tries to get over jet lag by getting out and about at the first opportunity could be delaying the body clock, said Dr Waterhouse. This is one reason why jet lag tends to last longer after an eastward flight than after a westward flight."Portable light sources - battery- operated visors, or torches - allow a traveller to switch on when necessary even during the flight," said Dr Waterhouse.Reuse content