This guide is for the traveller crossing several time zones with something important at the other end: the consultant flying overnight to a client meeting, the family heading east for a wedding, the student flying home for the holidays with exams waiting on return. Jet lag can make the first days of a trip foggy and frustrating. You cannot remove it entirely, but planning sleep, light and naps around your destination can shorten it noticeably.
This article is general information. If you have a sleep disorder, take regular medication or are considering melatonin or sleep aids, ask a doctor or travel clinic first.
What jet lag is
The CDC’s travel health reference, the Yellow Book chapter on jet lag disorder, describes jet lag as a sleep disorder caused by rapid travel across time zones, producing a temporary mismatch between your internal body clock and local time. It notes that jet lag is more than low energy. Symptoms can include disturbed sleep, poorer concentration, daytime sleepiness, general malaise and stomach upsets.
The diagnostic criteria the chapter cites refer to travel across at least two time zones, with symptoms appearing within one to two days after travel.
Why east is harder than west
According to the Yellow Book, most people find it easier to shift their body clock later than earlier, because the average internal rhythm runs slightly longer than 24 hours. Travelling west asks your body to stay up later, which comes more naturally. Travelling east asks it to go to sleep earlier.
The chapter gives average adaptation rates of about 1.5 hours a day after westward travel and 1 hour a day after eastward travel. Without any planning, a trip across six time zones eastward could take several days to adjust to fully.
Going east, chase the morning light. Going west, hold on to the evening light.
Before you fly
Choose your arrival time with care
The Yellow Book’s planning tips include choosing a flight that arrives at a time that lets you get the right amount of daylight at the destination.
Shift your sleep a little
The chapter suggests shifting sleep 1 hour earlier per day for eastward trips, or 1 hour later for westward trips, in the 2 to 3 days before departure. Even a partial shift reduces how far your body has to move after you land.
Consider a jet lag calculator
The Yellow Book mentions jet lag calculators that personalise timing for light, darkness, caffeine and melatonin based on your itinerary. They take the guesswork out of when to seek or avoid light.
During the flight
The Yellow Book’s in-flight tips:
- Time meals, sleep and light exposure to the destination time zone.
- Stay hydrated, as dehydration can worsen physical symptoms; avoid excess alcohol.
- Avoid sedative medications with long half-lives.
The chapter also notes that alcohol tends to fragment sleep, and that both alcohol and caffeine can contribute to dehydration.
A simple in-flight routine
1. Set your watch and phone to destination time when you board.
2. If it is night at your destination, use an eye mask and earplugs and try to sleep.
3. If it is day there, keep the window shade open where possible and stay awake.
4. Drink water regularly.
Using light: the most powerful tool
The Yellow Book explains that bright light in the morning tends to shift the body clock earlier, while light in the evening tends to shift it later. The best timing depends on the direction of travel and the number of time zones.
| Direction | Seek light | Avoid light |
|---|---|---|
| Eastward (for example, New York to London) | Early morning at the destination | Evening at the destination |
| Westward (for example, London to Los Angeles) | Evening at the destination | Very early morning |
The CDC chapter includes a tip sheet adapted from the Walter Reed Army Institute of Research that turns this into practical steps: for eastward travel, get bright light in the early morning and avoid light in the evening, using sunglasses or window shades; for westward travel, the reverse.
When crossing many time zones, the right timing can become counterintuitive, which is where a calculator helps.
After you arrive
The Yellow Book’s post-flight advice:
- Maximise natural light at the destination. Getting outdoors is one of the most effective things you can do.
- Avoid long daytime naps. They make it harder to sleep at night.
- Use short naps if needed. The chapter says naps of 20 to 30 minutes can help sustain alertness during the local day.
On the first day
Stay awake until a reasonable local bedtime if you can. A short walk in daylight, a meal at local mealtimes and a short nap if needed are better than collapsing at 3pm.
Caffeine
The chapter notes caffeine has a half-life of about 5 hours and advises avoiding stimulants in the hours before bed. A morning coffee at your destination is fine; an afternoon espresso may cost you the first night’s sleep.
Melatonin and sleep medication
The Yellow Book discusses timed melatonin and some prescription medications as options. It stresses that timing matters: melatonin taken at the wrong time can make the mismatch worse. It also cautions that melatonin is not regulated by the US Food and Drug Administration, so the dose in a product may differ from its label. Speak to a doctor or pharmacist before using either, especially if you take other medicines.
Short trips: do not adjust at all
The CDC’s tip sheet recommends that for short trips, such as less than two days, you avoid adapting to the new time zone and keep your sleep, activity and meal schedule on home time. Schedule important meetings for times that fall within your normal waking day.
Frequent travellers
The Yellow Book notes that planning matters most for frequent travellers, because insufficient sleep and circadian disruption have significant and additive health effects. If you cross time zones often, a consistent routine, calculator-based plans and recovery days after major trips are worth building into your schedule.
A sample eastward plan: New York to London
- Three days before: go to bed and get up 1 hour earlier each day.
- Flight day: evening departure; set watch to London time; eat lightly and try to sleep on board.
- Arrival morning: go outside for daylight early; avoid sunglasses unless advised by a calculator.
- Afternoon: short nap of 20 to 30 minutes if needed; no caffeine late in the day.
- Evening: dim lights; go to bed at a normal London bedtime.
The itinerary is illustrative; adjust it for your route.
A sample westward plan: London to Los Angeles
- Two or three days before: stay up and sleep in about 1 hour later each day.
- Flight day: daytime departure; set watch to Los Angeles time; stay awake for most of the flight.
- Arrival afternoon: spend time outdoors in the late afternoon and evening light.
- Evening: try to stay up until a normal local bedtime, even if you feel tired early.
- First morning: if you wake very early, keep lights low and rest rather than starting the day at 4am.
Jet lag checklist
- Arrival time chosen with daylight in mind
- Sleep shifted 1 hour per day for 2 to 3 days before departure
- Watch set to destination time on boarding
- Water during the flight; little or no alcohol
- Light sought and avoided at the right times for your direction
- Long naps avoided; short naps of 20 to 30 minutes if needed
- No caffeine in the hours before bed
- Melatonin or medication only after advice from a professional
- Trips under two days kept on home time
Takeaway
Jet lag comes from your body clock lagging behind local time, and it is usually worse after flying east. Shift your sleep before you go, live on destination time from the moment you board, use light at the right time of day, keep naps short and stay on home time for very short trips.
