Why Jet Lag Hits Some People Harder Than Others
Quick answer
Jet lag severity comes down to how far your circadian rhythm has to shift and which direction. Flying east requires advancing your internal clock, going to bed and waking earlier, which most people's biology resists more than the delay required flying west. Age, chronotype, and how well you manage light exposure on arrival all shift the difficulty further, which is why the same flight can wreck one traveler and barely touch another.
Want to try this yourself? Open the Sleep page.
Two people can take the exact same flight and come out the other side in completely different shape, one fine after a day, the other wrecked for most of the week. Jet lag severity isn't random. It comes down to a handful of specific, mostly predictable factors.
Why eastward travel is generally worse
Flying east requires your circadian rhythm to advance, essentially forcing your body to feel ready for sleep and wakefulness earlier than its natural rhythm currently expects. Most people's internal clocks resist advancing more than they resist delaying, which is why flying west, and effectively getting a longer day, tends to be the easier direction for most travelers to adjust to.
Your chronotype interacts with travel direction
Whether you're naturally more of a night owl or an early riser changes which direction hits harder. Night owls, whose internal clock already runs later than average, tend to adjust to westward travel more easily, while early risers tend to handle eastward, earlier-shifting travel better, since each starts the trip already partway shifted in the direction that specific journey demands.
Age reduces circadian flexibility
Circadian rhythms generally become less adaptable with age, and this shows up clearly in jet lag research, older travelers consistently report more severe and longer-lasting symptoms than younger ones on comparable trips, independent of overall health or fitness.
What actually speeds up recovery
Strategic light exposure has some of the strongest evidence behind it for shortening jet lag, deliberately seeking bright light at times that nudge your circadian rhythm in the direction you need, and avoiding it at times that would push the wrong way. This is more effective than most over-the-counter remedies, and it's free, though it does require a bit of planning around your specific flight direction and arrival time.
Our Sleep page pairs a fading sound environment with a sleep timer if you're trying to force an earlier or later bedtime while your body adjusts, and the article on middle-of-the-night waking is worth a look if jet lag has you awake at odd hours during the adjustment period.