Is jet lag worse going east or west?
For most people, jet lag is worse going east. About 75% of us have an internal circadian clock that runs slightly longer than 24 hours, so delaying it (traveling west) feels natural while advancing it (traveling east) fights our biology. People with internal clocks that are shorter than 24 hours – about 25% of people – find eastward travel easier and westward travel harder.
Why is jet lag often worse going east?
When we travel west, we need to delay our circadian clock to a later time, and lengthen our day. When we travel east, we need to advance our circadian clock to an earlier time and shorten our day.
To understand these statements, let's consider two scenarios:
- Westward travel needs a delay: If I am having lunch in New York, people in LA (3 time zones west of New York) are having breakfast. People in LA do things later than people in New York, so in order to shift from New York to LA time, we need to delay our clock. When you travel to LA from New York, and go to bed at 11pm LA time, that is the equivalent of 2am in New York time, so you have stayed up 3 hours later than normal and 'lengthened' your day by 3 hours.
- Eastward travel needs an advance: If I am having lunch in New York, people in Paris (6 time zones east of New York) are having dinner. People in Paris do things earlier than people in New York, so in order to shift from New York to Paris time, we need to advance our clock. When you travel to Paris from New York, and go to bed at 11pm Paris time, that is the equivalent of 5pm in New York time, so you have gone to bed 6 hours earlier than normal and 'shortened' your day by 6 hours (which is why it is hard to go to sleep).
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The chronotype exception
How does this relate to your circadian clock and chronotype? About 75% of people have an internal circadian clock with a ‘day’ length (or circadian ‘period’) longer than 24 hours. This is the equivalent of naturally traveling a little bit west every day and so most people find it easier to travel west, as they are 'going with their clock', not against it. These people tend to be more evening types who naturally stay up later and so find it easier to lengthen their day.
About 25% of people have a circadian clock with a ‘day’ length shorter than 24 hours. This is the equivalent of naturally traveling a little bit east every day and so a quarter of people find it easier to travel east. These tend to be morning types who prefer to sleep and wake up earlier and so they can more easily shorten their day.
Of course, circadian period and chronotypes are a continuum, ranging from extreme morning to extreme evening types, and so there will be a range of how easily people can adapt to different directions. Take the chronotype quiz >
19 quick questions to find your chronotype, free.
How long does jet lag last in each direction?
Without intervention, jet lag typically lasts about one day per time zone crossed. A 6-hour westward trip might resolve in 6 days for an evening type, but the same shift eastward may take longer.
With correctly timed light exposure and avoidance – the most powerful tool for shifting the circadian clock – adaptation can be compressed to 3–4 time zones per day in either direction. That cuts recovery from multiple days to sometimes barely any noticeable jet lag on many trips.
How to recover faster, regardless of direction
Light is by far the most powerful tool for resetting your circadian clock – and the timing of both light exposure and light avoidance differs based on travel direction. Seeing light at the wrong time can shift your clock in the wrong direction and make jet lag worse. Eastward travel generally requires seeing light in the morning and avoiding it in the late evening to advance the clock; westward travel typically requires seeing light in the evening and avoiding it in the early morning to delay the clock, although the exact timings depend on your flight, sleep preferences and chronotype.
Correctly timed melatonin can accelerate the light-driven shift in both directions, but it works as a supporting tool – not a replacement for proper light timing.
Want to know how long your own trip will take to recover from? Try the free Timeshifter jet lag app.
FAQ
Is jet lag worse going east or west?
For most people, jet lag is worse traveling east because it requires advancing the circadian clock earlier – which goes against the natural tendency of the clock to drift slightly later each day. About 25% of people, typically morning chronotypes with shorter-than-24-hour circadian periods, find westward travel harder and eastward travel easier.
Why is jet lag often worse going east?
Around 75% of people have an internal circadian clock with a period greater than 24 hours, which means their clock naturally drifts slightly later each day. Eastward travel requires shifting the clock earlier (a phase advance), which goes against this natural drift, whereas westward travel ‘goes with the flow’. The opposite is true for those with a clock shorter than 24 hours.
How does chronotype affect jet lag direction?
The longer the circadian period, the more likely you are to have a more extreme evening chronotype, and people with a clock longer than 24 hours generally find westward travel easier because their clock naturally wants to delay. People with shorter periods, who tend to be more morning types, generally find eastward travel easier because their clock naturally wants to advance. Chronotype and circadian period exist on a continuum, so the difficulty of each direction varies along that spectrum.
How long does jet lag last when traveling east versus west?
Without intervention, jet lag typically lasts about one day per time zone crossed, but it may take longer to adapt when traveling against your chronotype. With correctly timed light exposure and light avoidance – the most powerful tool for shifting the circadian clock – adaptation can be compressed to 3–4 time zones per day in either direction.
References
- Czeisler CA, Duffy JF, Shanahan TL, Brown EN, Mitchell JF, Rimmer DW, et al. Stability, precision, and near-24-hour period of the human circadian pacemaker. Science, 1999; 284(5423): 2177–2181.
- Eastman CI, Burgess HJ. How to travel the world without jet lag. Sleep Medicine Clinics, 2009; 4(2): 241–255.
- Fowler PM, Knez W, Crowcroft S, Mendham AE, Miller J, Sargent C, Halson S, Duffield R. Greater effect of east versus west travel on jet lag, sleep, and team sport performance. Medicine & Science in Sports & Exercise, 2017; 49(12): 2548–2561.
