Jet lag: what works, what does not, and why east is worse

General information for travellers, not medical advice. Speak to a pharmacist or doctor before taking anything, especially if you take other medication.

Jet lag is not tiredness. It is a mismatch between the clock in your head and the clock on the wall, and it affects sleep, digestion, concentration and mood independently. That is why a full night's sleep on arrival does not fix it, and why you can be wide awake at three in the morning and unable to think at three in the afternoon.

The mechanism is worth understanding, because it tells you exactly what to do.

Why the body clock drifts

The human circadian rhythm runs slightly longer than 24 hours in most people - closer to 24.2. Light resets it each day. Left in a bunker with no daylight, people drift later, which is why staying up late is easy and getting up early is not.

This asymmetry is the entire reason eastward travel is harder. Flying west lengthens your day, which your body already wants to do. Flying east shortens it, which it resists. The rough rule of thumb is one day of adjustment per time zone going east, and rather less going west.

Light is the lever. Everything else is minor.

Light exposure at the right time shifts the body clock. Light at the wrong time shifts it the wrong way, which is how people accidentally make jet lag last a week.

The simplified rule, based on your body clock rather than local time:

• Travelling east (you need to advance, to get sleepy earlier): seek bright light in the local morning and avoid it in the local evening. Sunglasses on the evening walk are not an affectation.
• Travelling west (you need to delay): seek light in the local late afternoon and evening, avoid bright light early in the morning.

One important trap: for large eastward shifts of eight hours or more, morning light in the first day or two can land on the wrong side of your body's low point and push you the wrong way. For those, get light in the middle of the local day for the first 48 hours, then shift earlier.

A plan that works for most trips

1. Two or three days before departure, shift your bedtime by an hour a day towards the destination. Even one hour helps.
2. Set your watch to the destination when you board, and start thinking in those terms immediately.
3. Sleep on the plane only if it is night at your destination. Otherwise stay awake, even if the cabin lights are off.
4. On arrival, get outside. Twenty to thirty minutes of daylight does more than any supplement.
5. Do not nap for more than 20–30 minutes on the first day, and not after mid-afternoon.
6. Go to bed at a plausible local hour - not 7pm because you are wrecked. Aim for 10pm and accept a rough first night.
7. Eat at local mealtimes from the first meal. Digestion has its own clock and food helps drag it across.

Melatonin, caffeine and alcohol

Melatonin is a timing signal rather than a sleeping pill, and it is the one supplement with reasonable evidence behind it for eastward travel. Small doses taken in the early local evening are what shifts the clock; large doses mostly make you drowsy. It is prescription-only in some countries and sold in supermarkets in others. Ask a pharmacist.

Caffeine is useful and easy to overuse. It helps you stay awake through the first local afternoon, which is genuinely the hardest part. It also has a half-life of around five hours, so a four o'clock coffee is still working at nine.

Alcohol is the one that consistently makes things worse. It shortens the time to fall asleep and wrecks the quality of sleep afterwards, and at altitude in a dry cabin it dehydrates you faster than on the ground.

The flight itself

Cabin air is drier than most deserts - relative humidity on a long-haul flight often sits below 20%. That is why you are thirsty, why your eyes hurt, and why food tastes bland: low pressure and dry air dull the perception of sweet and salty, which is exactly why airline meals are seasoned so heavily.

• Drink water steadily. Bring an empty bottle through security and fill it airside.
• Get up and walk every couple of hours. Circulation, not exercise, is the point.
• Eye mask and earplugs, or noise-cancelling headphones. Controlling light is controlling the clock.
• Take your shoes off, wear something you can sleep in, and accept that dignity is not the objective.
• Choose a window seat if you intend to sleep and an aisle if you intend to move. Deciding this in advance is worth more than any seat-hack.

Trips too short to bother

If you are away for two or three days across a large time difference, do not try to adapt at all. Stay on home time as far as your schedule allows, keep the important meetings in the overlap, and use light and caffeine tactically. Adapting to a new clock and then immediately adapting back is worse than not adapting.

What does not work

• Fasting for sixteen hours before landing. Popular, uncomfortable, and the evidence is weak.
• Sleeping tablets on the plane. They produce unconsciousness rather than restorative sleep, and they suppress breathing at cabin altitude.
• "Powering through" with no sleep at all. You will crash at four in the afternoon and wake at two in the morning, restarting the cycle.
• Special jet-lag diets. Meal timing helps; the specific composition of the meals does not, as far as anyone has demonstrated.

Give the first day nothing important

The most effective jet-lag strategy is scheduling. Do not land and go straight into the thing you came for. Give the first day a long walk, a simple meal, a market, an early night - things that are pleasant, outdoors, and forgiving if you are operating at 70%.

Two days later you will be on local time and the trip will effectively begin. Plan the itinerary that way and jet lag becomes a mild inconvenience rather than a third of the holiday.