The human body clock will gradually readjust to a new time zone, though a rule of thumb is that it takes one day per time zone going west to adjust, and 1.5 days per time zone going east. "The adjustment westwards is easier because the day is lengthened, whereas flying east is much harder because the day effectively gets squashed," says Professor Jim Horne of Loughborough University's Sleep Research Centre.
Why jet lag occurs
"Jet lag is primarily about trying to sleep or work at the wrong time relative to your body clock," says Dr Chris Idzikowski of the Edinburgh Sleep Centre. There are some variations, such as "social jet lag" experienced by different chronotypes - larks and night owls - and those who do shift work.
How the biological clock 's sleep-wake cycle is governed
"To get a good night's sleep you must have been awake for long enough that the pressure is on for sleep to happen," says Idzikowski. "Over and above that the biological clock has around a five-hour window where it is happy for sleep to occur."
Two key phenomena govern the biological clock's workings: the presence of light, and melatonin. Increasing amounts of light at dawn are detected by photoreceptive ganglions in the retina which feed information along the optical nerve, branching into the suprachiasmatic nucleus located in the hypothalamus, which in turn controls the biological clock. Still with us? "The first part of the brain that knows about light and dark is the biological clock." (The ganglions are particularly sensitive to blue light, which can be filtered out using orangetinted glasses.)
Meanwhile, melatonin, which causes drowsiness, is secreted by the pineal gland in response to darkness. "It slows down the body clock, but it is suppressed by light, such as dawn, and that speeds the body clock up again," says Idzikowski.
"Those two time periods can be manipulated according to new time zones."
**What to do
\1. Think locally.** If you're travelling across more than three time zones, use local light information to adjust the body clock. For instance, if you are flying to New York - perhaps you set off at 10am BST and arrive in the afternoon - expose yourself to light for the period that would have been night-time at your departure, then avoid light afterwards.
\2. Work the web. Go to bodyclock.com and input your usual waking time, plus information on your departure and arrival times.
The website generates instructions on either seeking or avoiding light at specified times. Synchronisation can also be helped by:
\3. Make some dietary adjustments. Trying reducing food intake for 24 hours before you fly, and resynchronise the digestive system to the rhythm of the local destination. If you want a more developed dietary approach, consider the Anti-Jet-Lag Diet, said to have been tested on US military personnel.
4. Try some exercise. Evidence suggests that exercising between 5pm and 7pm at the destination can help the body clock to adjust, says Idzikowski.
5. Should you sleep on the plane? Not necessarily. "Ignore flight times and look at synchronising to local times," says Idzikowski. Setting your watch to the destination time the moment you board the plane will also help you to adjust.
Want more Wired UK magazine? Make sure you get your copy every month - subscribe online today.
This article was originally published by WIRED UK
