Most long-distance travelers have felt the discombobulation of changing time zones: being excessively tired during the daytime but struggling to sleep at night.
Jet lag often emerges when people hop several time zones. The majority struggle more when flying east because our body clock is typically just over 24 hours. "It's a little bit harder to shift earlier," Helen Burgess, a professor at the University of Michigan's Sleep and Circadian Research Laboratory, told Live Science.
What is jet lag?
Jet lag is a mismatch between our internal body clock and our time zone.
"Jet lag derives from the simple fact that jets travel so fast they leave your body rhythms behind," Dr. Charles Czeisler, a professor of sleep medicine at Harvard Medical School, told Live Science. Before flights, people traveled overland or via ship so slowly that their circadian clock didn't get out of alignment.
Jet lag is the body's normal response to skipping time zones. "If the circadian system is working correctly, you should have a problem with jet lag," Czeisler said. But some populations — such as older people, frequent fliers or those with mood or sleep disorders — are more likely to feel symptoms.
Jet lag might seem trivial, but even a small dose can have serious health implications. When the clocks move forward — essentially causing an hour's jet lag — there's an increase in fatal car accidents, Czeisler said. Getting behind the wheel straight after a long-haul flight is dangerous because a lack of sleep is a known cause of car crashes.
Shifting circadian rhythms can even "flip people into mania or depression," Czeisler said. Research has found that jet-lag-related mental health conditions such as depression and hypomania can be severe enough to require hospitalization, while another study has shown that chronic jet lag could increase the risk of neurological disorders.
Minimizing jet lag
The best way to adjust to your new time zone is through light exposure. "Light is the strongest signal that shifts the timing of the clock," Burgess said.
But the timing has to be right: exposure to light at the wrong time can push your clock in the wrong direction, making jet lag last longer.
Around two or three hours before your usual wake-up time, your body clock switches from interpreting light as evening light — making you sleepy — to morning light, which wakes you up. "Light before the crossover point will shift you later, and light after the crossover point will shift you earlier," Burgess said. This is why napping isn't always the right solution.
If you usually wake up at 6 a.m., your crossover point will be around 3 a.m. If you travel to a time zone six hours ahead and land at 7 a.m., your internal clock reads around 1 a.m. So your body interprets the morning light as evening light, pushing your clock later rather than helping you adjust.
To get light when you need it, go outside, use light boxes, or put on wearable light therapy devices. To avoid light when it will push you in the wrong direction, nap, stay inside, or wear sunglasses or glasses that block blue light.
To minimize jet lag further, stay hydrated, avoid alcohol, and be mindful of caffeine intake — "maybe just one cup of coffee" at strategic times, Burgess said, noting that caffeine's long half-life makes it harder to sleep later. Adjusting to local mealtimes as soon as possible also helps. Some people may speak to medical professionals about whether melatonin is suitable for them.
You can also prevent jet lag by shifting your body clock to the new time zone before you arrive. "On average, we can only shift the clock earlier by about an hour and a half a day," Burgess said — so adjusting to a large time difference requires starting well before your flight.
When Burgess tried this herself, she felt disconnected from the world around her because everyone was asleep during her waking hours. "I just felt really, really isolated," she said.
If fully switching to the new time zone before you depart is too challenging, even nudging your schedule closer by an hour each day for a few days will help. "It can make a huge difference," especially for those flying east, Burgess said. "Take the five or 10 minutes to plan it out, and that's going to really help."