Managing Jet Lag

Jet lag (or circadian misalignment) occurs when rapid travel across multiple time zones places the internal circadian clock out of phase with the local environment. The suprachiasmatic nucleus (SCN) in the hypothalamus drives a biological rhythm of approximately 24 hours — one that cannot shift instantly to match a new time zone.

Jet lag symptoms arise because different physiological systems reset at different rates. Melatonin, cortisol, body temperature, digestion, and cognitive function all have their own circadian rhythms, and these realign at different speeds — producing the mixed-up feeling of jet lag for days after arrival.

Symptom	Cause	Typical Duration
Daytime sleepiness	Sleep phase misaligned with local day	1–5 days depending on time zones crossed
Night waking / insomnia	Circadian alerting signal active at wrong time	2–7 days
Digestive disruption	Gut microbiome has its own circadian rhythm	2–4 days
Cognitive impairment	Sleep disruption and circadian misalignment	1–5 days
Mood disturbance	Disrupted serotonin and cortisol rhythms	1–3 days

As a rough rule, most people require approximately one day of recovery per time zone crossed without active intervention. Active strategies can roughly halve this.

The human circadian clock naturally runs slightly longer than 24 hours — approximately 24.2 hours on average. This means the brain finds it easier to delay the clock (stay up later and wake later) than to advance it (go to sleep earlier and wake earlier).

• Westward travel requires delaying the clock — staying up later at the destination. Because the brain is already inclined toward clock delay, westward adjustment is easier. A rule of thumb: recovery takes about half a day per time zone crossed westward.
• Eastward travel requires advancing the clock — going to sleep earlier and waking earlier at the destination. This fights against the clock's natural tendency. Recovery takes about one day per time zone crossed eastward.

Travel Direction	Clock Adjustment Needed	Difficulty	Recovery Estimate
West (e.g., London to New York, −5 zones)	Delay clock by 5 hours	Moderate	~2–3 days with intervention
East (e.g., New York to London, +5 zones)	Advance clock by 5 hours	Hard	~4–5 days with intervention
West (>7 zones)	May be easier to go the other direction	Context-dependent	Variable

Tip: If crossing more than 9 time zones westward, travelling eastward (the long way) may actually be faster to adapt to, despite seeming counterintuitive — you are only advancing by a smaller number of zones.

Light is the primary zeitgeber for the circadian clock and the most powerful tool for resetting it after travel. The key principle is phase-shifting: light exposure at the right time of the local day can advance or delay the clock to align with the new environment.

The phase response curve (PRC) for light tells us:

• Bright light in the morning (at the destination's local morning) advances the clock — helpful for eastward travel
• Bright light in the evening delays the clock — helpful for westward travel
• Avoid bright light at the wrong time — exposure during your origin body's subjective night will worsen, not help, realignment

Travel Direction	Seek Light When	Avoid Light When
Eastward	Early local morning (6–9am at destination)	Late evening at destination
Westward	Late afternoon and early evening at destination	First 2 hours of local morning

Warning: Getting light exposure at the wrong time (e.g., early morning sun after eastward travel when your body thinks it's the middle of the night) can delay your recovery. When in doubt about timing, tools like the Timeshifter app (designed with circadian scientists) can generate personalised light schedules.

Melatonin is a chronobiotic (clock-shifter) rather than a sedative. At low doses taken at the right time, it signals the brain that it is nighttime and helps advance or maintain the sleep phase. It does not knock you out — it nudges the circadian clock.

Most over-the-counter melatonin doses (3–10 mg) are significantly higher than physiologically necessary. Research by MIT sleep scientist Richard Wurtman found that 0.3–0.5 mg is as effective as higher doses for phase-shifting, without the grogginess the next morning that higher doses can cause.

Travel Direction	When to Take Melatonin	Dose
Eastward travel	At destination's local bedtime (10–11pm) for 3–5 nights	0.3–0.5 mg
Westward travel	Generally less necessary; if used, take 1–2 hours before sleep	0.3–0.5 mg
Short trips (<3 days)	Consider not adjusting — may be easier to stay on home schedule	N/A

Melatonin is not regulated as a drug in the US (sold OTC as a supplement) but is prescription-only in many European countries. Its side effects are mild at low doses; at high doses (5–10 mg), morning grogginess and vivid dreams are common. It is generally considered safe for short-term use.

Proactive strategies before and during a long-haul flight can significantly accelerate post-arrival adjustment.

Pre-flight (2–3 days before):

• For eastward travel: advance your sleep time by 30–60 minutes per day; avoid evening light; take low-dose melatonin at the target destination's bedtime
• For westward travel: delay bedtime by 30–60 minutes per day; seek evening light
• Avoid alcohol in the 2–3 days before to ensure baseline sleep quality

In-flight:

• Set your watch to the destination time zone immediately on boarding
• Sleep during the flight if it is nighttime at the destination; stay awake if it is daytime
• Avoid alcohol — it dehydrates and fragments sleep without aiding adaptation
• Hydrate actively; cabin air is typically 10–20% humidity (well below the 40–60% comfort range)
• Use a sleep mask and earplugs if sleeping; seek bright overhead light if staying awake

In-Flight Action	Purpose
Sleep mask + earplugs	Protect sleep quality during flight rest
Avoid caffeine if sleeping in-flight	Allows flight sleep to consolidate
Caffeine strategically if staying awake	Maintains alertness for arrival adjustment
Move / stretch hourly	Circulation and reduces DVT risk