Passengers on long-haul flights are being urged to wear sunglasses in a bid to reduce the effects of jet lag.
Scientists discover wearing sunglasses can help beat jet lag
Scientists in Edinburgh have found that people can adjust their body clocks when travelling to different time zones by altering their light patterns.
Jet lag, which causes feelings of sleepiness and muscle inefficiency, is affected by the biological clock.
The study, conducted by Edinburgh Sleep Centre for British Airways, monitored more than 1,000 passengers.
Dr Chris Idzikowski, director of The Edinburgh Sleep Centre, said that without using sunglasses it took a day to recover for every hour of time difference travelled westwards.
He said: "The biological clock is 20,000 nerve cells in the brain, it is a physical thing and not made up like many people think.
"When passengers are travelling west it's like a long day for the biological clock but when flying east, the clock tries to go into reverse which is obviously harder."
Dr Idzikowski has drawn up a jet lag checker for passengers, which tailors the amount of time and when passengers are to wear sunglasses.
He added: "The internal body clock steps up at dawn which is when we can manipulate exposure to light, it's a way of fooling the biological clock.
"I have used this technique on a flight but you have to be aware of immigration officials as they can ask you to take them off, which weakens the outcome."