How to beat jet lag: light, sleep and timing

Jet lag happens when your body clock is still running on home time after you cross time zones. The fastest way to reset it is light at the right time of day, combined with switching your sleep and meals to local time as quickly as you can. As a rule of thumb, adjusting takes about a day per time zone when travelling east and somewhat less when travelling west. The jet lag calculator works out the shift and a simple plan from your departure and destination time zones; this guide explains the reasoning behind it.

Why jet lag happens

Your sleep, alertness, body temperature, hunger and digestion follow a roughly 24-hour circadian rhythm, set by a master clock in the brain. Light reaching the eyes is its strongest cue. A flight moves you to a new time zone in hours, but the clock shifts only gradually, so for several days you can be sleepy at midday and wide awake at 3 am. The NHS lists the main symptoms as difficulty sleeping at bedtime and waking in the morning, tiredness, difficulty staying awake during the day, poor sleep, and problems with concentration and memory, sometimes with indigestion or nausea. Jet lag is different from travel fatigue, which comes from the journey itself and fades after a good night's sleep: a long flight from north to south causes tiredness but no jet lag.

Why east is harder than west

Most people's internal clock runs slightly longer than 24 hours, so it finds it easier to delay, going to bed later, than to advance, going to bed earlier. Flying west, say from London to New York, means staying up a few hours later than usual, which most people manage. Flying east, from New York to London or London to Tokyo, means trying to fall asleep while your body thinks it is still evening, which is harder. That is why the calculator assumes about one hour of adjustment a day going east and about one and a half going west: five hours east suggests about five days, five hours west about four. Crossings of more than 12 hours are treated as the shorter way round. For short trips of two or three days, the NHS suggests you could stay on home time to avoid adjusting twice.

Before you fly

• For bigger shifts, move your bedtime and wake time by about an hour a day for a few days before you leave: earlier for trips east, later for trips west. The calculator suggests how many days.
• Get plenty of rest beforehand; starting a trip short of sleep makes everything worse.
• Check local times at your destination with the time zone converter, remembering that daylight saving can change the difference by an hour.

On the plane

• Set your watch or phone to destination time when you board, and sleep or stay awake to match it.
• Use an eye mask and earplugs if it is night at your destination.
• Drink water, and walk around the cabin and stretch regularly.
• Go easy on alcohol and caffeine, which can make jet lag worse.

After you arrive

Switch to local time straight away: eat at local mealtimes and go to bed at a normal local bedtime. Then use light deliberately, because morning light moves the body clock earlier and evening light moves it later:

• After flying east, get bright daylight in the morning and avoid bright light late in the evening. For very large eastward jumps of eight hours or more, early morning light can land at the wrong point in your body's cycle and push the clock the wrong way, so for the first couple of days seek late-morning light instead.
• After flying west, get daylight in the late afternoon and early evening, and stay up until a normal local bedtime.
• Avoid long daytime sleeps. If you must nap, keep it to 20 to 30 minutes and before mid-afternoon.
• Use caffeine in the morning rather than late in the day; the caffeine calculator shows how much will still be in your system at bedtime.

The sleep calculator can help you pick a wake-up time for your first local night, and if you work across time zones regularly, Working across time zones covers scheduling meetings without wrecking anyone's sleep.

Melatonin and sleeping tablets

Melatonin is the hormone your body releases in the evening to signal night. It is sold as a supplement in some countries, but in the UK it is prescription-only, and the NHS does not recommend it for jet lag because there is not enough evidence that it works. Sleeping tablets can help with short-term sleeplessness, but they can be addictive and should only be used briefly. Talk to a doctor or pharmacist before taking either, especially if you take other medicines, are pregnant or have a health condition. For most trips, light, timing and patience do most of the work. This guide is general information, not medical advice.