Jet lag & daylight-saving

Jet lag is your clock failing to fast-forward or rewind on demand — and the direction of the flight decides how much it hurts. This page turns the parent topic's summary into a working protocol: light exposure schedules, timed low-dose melatonin, and the east-vs-west asymmetry, plus what the daylight-saving shift teaches us every year.

Why East Is Harder Than West

The asymmetry comes straight from the clock's hardware. Measured under forced-routine conditions, the human circadian pacemaker runs about 24.2 hours (Science, 1999) — slightly longer than a day. A long internal day drifts later naturally, which means phase delays (sleeping later) come easily and phase advances (sleeping earlier) come hard. Flying west asks your clock to do the easy thing; flying east asks it to do the hard thing.

The practical rule of thumb that follows: count on roughly half a day to a full day of adjustment per time zone crossed westbound, and closer to a day or more per time zone eastbound. A New York-to-London flight (five zones east) can take the better part of a week to fully clear; the return flight often barely registers after two or three days. It isn't your imagination — the same trip has two different prices. Recovery also slows with age, so budget more days than the rules of thumb suggest.

The Melatonin Protocol

The strongest single intervention is also the cheapest: low-dose melatonin at the right time. The Cochrane review of randomized trials concluded that melatonin taken at bedtime in the destination time zone reduced jet lag, and that doses of 2–5 mg were effective — with 0.5 mg performing similarly while producing less daytime sleepiness (Cochrane Database of Systematic Reviews, 2002). The schedule that fits the evidence:

• 🌙 Start the night you arrive. Take 0.5–1 mg at destination bedtime; continue for two to four nights, or until sleep feels normal.
• ⏱️ Timing is the dose. Melatonin's clock-shifting effect depends on taking it relative to your body's evening — bedtime dosing on arrival is the schedule the trials support.
• 🚗 Expect sleepiness. Don't drive or operate anything dangerous after a dose; melatonin makes you drowsy — that's partly the point.

⚠️ Melatonin is a supplement, not a regulated drug: contents vary between brands, and it can interact with medications such as blood thinners. If you take regular medication, are pregnant, or are dosing a child, check with a clinician first — and note that measured supplement contents frequently diverge from labels, so third-party-tested brands are worth the effort.

Light: The Steering Wheel for Travel

The master signal is also the main steering mechanism for re-entrainment. The rule of thumb is direction-specific, and it reverses the instinct most travelers have:

• 🌅 Eastbound: seek morning light, dodge late-evening light. Morning exposure advances the clock toward the earlier destination schedule; bright evenings fight the advance and prolong the jet lag.
• 🌇 Westbound: seek afternoon and evening light, skip bright early mornings. Late-day light delays the clock toward the later destination schedule; an early-morning run does the opposite of what you need.
• 📅 Start before you fly. For consequential trips, shifting bedtime 30–60 minutes per night toward the destination for several nights before departure reduces the total shift on arrival (Sleep Medicine Clinics, 2009).

On the plane itself, the useful moves are mundane: set your watch to destination time, sleep or stay awake according to that clock, skip the alcohol (it fragments whatever sleep you do get — see the sleep saboteurs topic), and treat caffeine as a destination-morning tool only. The same logic says don't board the flight already sleep-deprived: a weekend of bad sleep before departure stacks sleep debt on top of the clock shift, and the two compound.

Arrival discipline matters as much as the flight. Stay awake until a local bedtime that's plausibly within reach, get the direction-correct light dose outdoors rather than through a hotel window, and eat on local time from the first meal. A short nap on arrival is fine — 20 minutes, before mid-afternoon — but a four-hour crash at 2pm local time is simply rebooking the jet lag for later in the week.

The Protocol, by Direction

Daylight-Saving Time: The One-Hour Experiment

Twice a year, hundreds of millions of people get jet lag without boarding a plane. The spring transition — losing an hour, effectively an eastward shift — is the informative one. Swedish registry data showed a modest but real rise in heart attacks in the days after the spring shift, concentrated in the first three days, with the reverse pattern in autumn (New England Journal of Medicine, 2008). A Michigan study found roughly a quarter more heart attacks on the Monday after springing forward (Open Heart, 2014), and US data spanning two decades linked the week after the spring transition to about a 6% rise in fatal traffic accidents — tens of deaths per year — with no equivalent fall-transition effect (Current Biology, 2020).

These are short-term, population-level blips; your personal risk from one lost hour is small. The deeper lesson is what the one-hour shift proves: even a single hour of circadian disruption measurably shows up in cardiovascular and accident statistics. The American Academy of Sleep Medicine's position, grounded in this biology, is to abolish seasonal time changes in favor of permanent standard time, which aligns more closely with the human clock (Journal of Clinical Sleep Medicine, 2020). The policy argument follows the biology: permanent standard time keeps morning light aligned with the clock, while permanent daylight-saving — the other proposal — pushes light later into the evening, which the circadian literature says is the wrong direction for the average sleeper.

Questions, Answered Briefly

• 💊 Is 0.5 mg of melatonin really enough? In the Cochrane trials, low doses reduced jet lag comparably to 2–5 mg with less daytime sleepiness — more is not better.
• 🍽️ Does the "fast on the plane" trick work? The anti-jet-lag diets that skip in-flight meals are mechanistically plausible, but trial support is sparse — the Cochrane review does not back them over timed light and melatonin.
• 🧭 What about a five-day trip? That's the break-even zone. If obligations are flexible, partial anchoring to home time works; if you must perform on local time from day one, adapt fully.
• 😴 Do sleep medications help? They force sleep without shifting the clock — acceptable once or twice, not a re-entrainment strategy. Tolerance and hangover effects argue against relying on them (see the saboteurs topic).

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