Jet Lag: What Actually Helps

Why direction matters so much

Flying east is harder than flying west, and the gap is substantial. Travelling east shortens your day and requires falling asleep earlier than your body wants, which is the harder direction to shift. Travelling west lengthens the day and requires staying up later, which most people manage without much difficulty.

The rough rule is that the body adjusts about an hour a day going east and closer to an hour and a half going west, though this varies considerably between individuals. A five-hour eastbound shift is a genuine several-day proposition; the same shift westbound is usually shorter.

This has a planning consequence. If you have any flexibility about which leg of a trip carries the important commitments, put them after the westbound leg rather than the eastbound one.

Light is the main lever

The body clock takes its strongest cue from light exposure, which makes light timing the most effective tool available and the one most people use accidentally rather than deliberately.

Getting light at the wrong time can push your clock in the wrong direction. Broadly, when travelling east you want morning light at the destination and to avoid bright light in the local evening. Travelling west, you want light in the local late afternoon and evening, which helps hold you awake until a reasonable bedtime.

For large time shifts, the timing becomes less intuitive, because light before or after your body's own low point has opposite effects. If you cross many zones regularly, it is worth reading a proper source on light timing rather than following a general rule.

Get onto local time immediately

Change your watch and your phone on boarding, and start thinking in destination time from that moment. It sounds trivial and it changes the decisions you make for the rest of the journey.

The single most valuable rule on arrival is to avoid a long nap on the first day. A short rest of twenty or thirty minutes is survivable; two or three hours in the afternoon feels wonderful and reliably adds days to the adjustment because it removes the sleep pressure you need to fall asleep at a local bedtime.

Eat on local mealtimes as well. Meal timing is a weaker cue than light but it is a real one, and it also keeps you upright and outside rather than in a dark room.

What the popular remedies are worth

The market for jet lag products is larger than the evidence behind most of them. Roughly:

• Melatonin has genuine support for shifting the body clock, but the timing and dose matter a great deal and taking it at the wrong hour can push you the wrong way. It is worth discussing with a clinician rather than guessing, and it is regulated differently in different countries.
• Hydration is worth attending to because cabin air is very dry, though it addresses the discomfort rather than the clock itself.
• Alcohol on the flight is actively counterproductive, degrading sleep quality and worsening dehydration.
• Sleeping tablets can get you through the flight but do not shift the underlying clock, and can leave you groggy at exactly the point you need daylight and activity.

Should you adjust before you go?

Shifting your sleep by an hour or two in the direction of travel for a few days beforehand genuinely helps, particularly eastbound where the adjustment is harder. It reduces the size of the shift you have to make on arrival.

It is worth being realistic about whether you will do it. For a large time difference, pre-adjusting enough to matter would disrupt your life at home more than the jet lag disrupts the trip. The pragmatic version is a couple of days of modest shift before a long eastbound flight, and no attempt at all for a short trip.

Short trips are a special case

For a trip of two or three days across a large time difference, fully adjusting is neither achievable nor necessarily desirable, since you would adjust just in time to fly home and adjust back.

In that case it can be better to stay closer to home time, scheduling important commitments during the hours that overlap with your normal waking day. It is not comfortable, but it avoids paying the adjustment cost twice for very little benefit.