Jet lag: a practical, research-backed protocol

The circadian system adjusts to a new time zone at roughly 1 time zone per day on its own. With deliberate light exposure timing, that rate roughly doubles. The biology is well-mapped; the practical protocols are simpler than they look.

Eastward vs westward#

Eastward travel is harder for most people. Why: the human circadian period is slightly longer than 24 hours, so delaying (westward) the rhythm is easier than advancing (eastward). The same number of time zones causes more disruption and longer adjustment when going east.

A useful rule: westward, you stay up later than usual. Eastward, you go to bed earlier than usual. Match light exposure to those goals.

The phase-response curve to light#

The human PRC to bright light has two functional zones:

• Light in the late evening and early biological night → phase delay. Your clock shifts later.
• Light in the late biological night and early morning → phase advance. Your clock shifts earlier.

The crucial point: "morning" and "evening" mean your biological morning and evening, which is your home time when you've just arrived in a new zone.

A practical eastward protocol#

You've flown from London to Bangkok (+6 hours).

On arrival (Day 0): Stay outdoors in daylight in the local afternoon. Avoid bright light in the local evening (which is your biological night just before your normal wake; light here would shift you the wrong way). Aim for sleep at the local bedtime even if not tired.

Days 1–3: Maximise morning light exposure at the destination. Get outdoors as soon as possible after local sunrise. Minimise late-evening light. Keep meal timing aligned with the new zone.

Caffeine timing: Use caffeine in the local morning. Stop caffeine at least 8 hours before intended local bedtime; your slow-metaboliser buffer may need to be longer.

A practical westward protocol#

London to New York (–5 hours).

On arrival (Day 0): Stay up: bright light in the local evening helps delay your clock. Push bedtime later than feels natural.

Days 1–3: Light exposure in the late afternoon and evening at the destination. Avoid bright morning light initially (especially before about 04:00 destination time, which is your biological middle of the night).

What about melatonin?#

Melatonin has the most-evidenced jet lag use case of any sleep supplement. It's a POM in the UK; the licensed product is Circadin (see melatonin-uk-regulatory). For frequent long-haul travel, discussing prescribed melatonin with a GP is reasonable. We don't provide dosing here.

What about meal timing?#

Some chrono-nutrition research suggests aligning meal timing with the destination zone before arrival can accelerate adjustment. The evidence is less consolidated than the light-timing evidence but the cost is low. Skip the in-flight meal if it falls at destination night-time.

Common errors#

• Sleeping in late at the destination after eastward travel. Misses the morning light that would advance your clock.
• Bright phones in bed at the destination. Particularly damaging eastward when you're trying to advance.
• Trying to be productive in the first 24 hours. Acute cognitive performance is poor; accept a slower start.
• Wearable sleep tracking on the first night. Numbers will look bad. That's expected.

What we'd actually say#

Light timing does the most work. Outdoor light in the destination morning (eastward) or late afternoon/evening (westward), aggressively for 3–4 days, is the cheapest jet lag intervention and the best-evidenced.

For occasional 1–3 zone trips, you'll mostly adjust naturally in 2–3 days regardless. For 6+ zones, deliberate light timing matters more. For frequent long-haul work travel, discussing prescription melatonin with a GP makes sense.

When to talk to a clinician#

• Persistent insomnia or daytime sleepiness lasting weeks after travel
• Frequent long-haul travel as part of work: occupational health input may be useful
• New-onset cardiovascular symptoms in older travellers — long-haul flights carry separate risks