Jet lag is a light problem: the long-haul protocol
A study published in SLEEP in April 2025 followed 60,000 trips and 1.5 million nights. It found something most travellers get wrong: you sleep enough again long before you sleep properly again.
The work came out of the National University of Singapore with data from a consumer sleep tracker. Sleep duration recovered to baseline in roughly two days. The timing of sleep, and its architecture, took more than a week, and the effect was worse travelling east. That gap is the whole reason a trip can feel fine on paper and wrong in the body on day five.
Melatonin and a dark cabin are not the main instrument. Light is. Your internal clock reads light, and it reads it differently depending on when the light arrives relative to your own low point of body temperature, which sits roughly two hours before your usual waking time. Light after that low point advances the clock. Light before it delays the clock. Everything below follows from those two sentences.
Flying east: you need to advance
Three days before. Move your bedtime and your wake time thirty to sixty minutes earlier each day. Take the morning light of your departure city as early as you can. This is the single highest-return thing you will do and it costs nothing.
On board. Set your watch to the destination on boarding and eat on the destination's schedule, not the cabin's. If it is night where you are going, sleep. If it is day, stay awake and keep the window shade up. Caffeine stops twelve hours before your intended destination bedtime.
On arrival. Get outside within the first hour of local morning, for thirty minutes minimum, without sunglasses. Avoid bright light in the local late evening. If you arrive in the local small hours, the light you want is later that morning, not immediately: light too early on an eastward trip pushes your clock the wrong way.
Flying west: you need to delay
Westward is the easier direction because the body drifts later on its own. Push your bedtime later in the days before departure, take light in the local late afternoon and early evening on arrival, and resist the nap that arrives at four in the afternoon. If you must sleep, twenty minutes, sitting up, before three o'clock.
Duration comes back in two days. Timing takes a week. Plan the trip around the second number, not the first.
Food, training and the first forty-eight hours
Eat at destination meal times from the first meal, even if you are not hungry, and put protein in the first one. Train easy on day one, outside and in daylight, and leave the hard session for day three. A long walk on arrival afternoon does more for the clock than an hour in a basement gym, because the point is the light rather than the effort.
This is also why the address matters more than the flight. A room that cannot be made dark at ten in the evening local time will hold you in the wrong phase for the whole stay, whatever you did on the plane. It is the one variable you cannot fix once you have arrived.
What this changes in a stay
The NUS finding, that timing takes a week to come back while duration takes two days, is the reason we ask for the flight before we propose an address. A room that cannot be made dark at ten in the evening local time will hold you in the wrong phase for the whole stay, and that is a question about the place rather than about the journey. We choose the address for the direction you are flying, we set the first two days around light rather than around activity, and where the stay calls for it we put you in touch with the people who work on sleep.
Frequently asked
How many days does jet lag last?
Sleep duration usually returns to normal within about two days. The timing and the structure of your sleep take more than a week, and longer travelling east, according to the NUS study published in SLEEP in April 2025.
Is jet lag worse flying east or west?
East. The body drifts naturally towards a later rhythm, so delaying the clock westward is easier than advancing it eastward.
Should I get morning light immediately after landing?
Going east, yes if you land in local morning, no if you land in the small hours: wait for later that morning. Going west, take the light of the local late afternoon instead.
Does melatonin fix jet lag?
It can help shift the clock at the right time of day, but it is secondary to light exposure and to a room that can be made properly dark. Anything you take is a matter for your doctor.