Jet lag and shift work

Jet lag is a circadian problem, and the treatment is circadian, which is why melatonin helps and why it does not work the way people expect.

Melatonin is a timing signal. It is released by the pineal gland in the evening in response to darkness and it tells the body that night has begun. Taking it at the destination's bedtime for the first few nights after arrival advances the rhythm and reduces jet lag, and this is the best-established use. The timing is the active ingredient, not the dose — the trials used low doses (0.5-3 mg), higher doses are not clearly better, and taking it at the wrong hour shifts the rhythm in the wrong direction and makes things worse. It is not a general sleeping pill and it does not treat ordinary insomnia in the way a hypnotic does.

Light is the other lever and it is stronger than the tablet. Light is the dominant zeitgeber — the signal that sets the clock — and the rule is that light in the biological morning advances the clock and light in the biological evening delays it. Practical translation for travel: seek morning light at the destination and avoid bright light in the destination's late evening. For an eastward trip (which is harder) you want morning light; for a westward trip you want evening light. Getting this backwards extends the jet lag rather than shortening it.

The other measures. Shift the sleep schedule before travelling where the trip is long; hydrate; avoid alcohol on the flight, which fragments the second half of the night and dehydrates; eat at the destination's mealtimes; and get outside in daylight on arrival rather than napping in a dark room.

Shift work is the same problem chronically. Rotating shifts, and especially backwards rotation, produce a persistent circadian misalignment that is associated with metabolic and cardiovascular risk. The measures with evidence are forward-rotating schedules where the employer allows it, strategic napping before a night shift, bright light during the shift and darkness on the way home (sunglasses, a dark bedroom), caffeine early in the shift rather than late, and consistent sleep timing on days off where possible. Melatonin before a day sleep can help, with the same timing caveat. None of this removes the health cost of long-term night work; it reduces it.

What not to do. Do not take a large melatonin dose at a random time. Do not use alcohol as a sleep aid on a flight. Do not use sedating antihistamines to force sleep across time zones and then drive at the destination.