Here’s why jet lag really happens, who it tends to hit the hardest, and how to minimize its impact trip by trip. It occurs when we change time zones too quickly for our internal clocks to catch up to our new surroundings. If, for example, you fly from Los Angeles to New York City in one day, come 11 p.m. at your destination, your body will still feel like it’s 8 p.m. This mismatch can cause fatigue, difficulty sleeping at the appropriate times, and a number of other side effects. Not only does the circadian clock dictate when we feel tired and awake, but it also plays a role in keeping other processes in the body—from digestion to hormonal release—on schedule (hence the nickname “master clock”). Even though light shifts throughout the year as the days get longer and shorter, these changes happen gradually enough that our clocks can easily adjust. When we take a flight halfway around the world in one day, though? That’s bound to throw the clock, and everything it oversees, out of whack. “When you travel across time zones rapidly, you change the light-dark cycle so quickly that the body clock can’t keep up,” explains Steven Lockley, Ph.D., a neuroscientist and the co-founder and chief scientist at Timeshifter. There’s a reason that we don’t get “ship lag,” he adds, since traveling via slower modes of transportation gives our clocks adequate time to adjust to changes in the light-dark cycle. “Never in nature would you have experienced a change in the light-dark cycle of, say, seven hours in a day… It’s completely unnatural, and your brain doesn’t know how to cope with it as it thinks you are waking and sleeping at the wrong time,” Lockley says. “So what it does is it has to reset itself—but it can’t reset itself seven hours in one day.” Until our clocks fully reset to our new time, we won’t feel our best in our new environment. However, Lockley adds, some of us will be able to adjust faster due to our sleep chronotype. As mentioned earlier, the timing of our personal clocks differs slightly. Instead of a precise 24-hour loop, some may run on a 23.5-hour cycle, others a 25-hour cycle. Those who have a shorter clock tend to be morning people, while those who have a longer type are more night owls. “Most people find it easier to travel west,” Lockley explains, “and that’s because three-quarters of people have an internal circadian clock longer than 24 hours, which is the equivalent of going west a little bit each day.” Since you’re traveling in the direction that your clock naturally wants to go, you may find it easier to overcome jet lag upon landing. (Of course, you’ll have the opposite experience after the return flight.) If you don’t want to wait for jet lag to naturally take its course, Lockley and Zeitzer say it’s possible to accelerate the transition and reset your internal clock using strategically timed light and dark exposure. However, he adds, the lighting required to get your circadian rhythm back on track will depend on the number of time zones traveled, the direction of travel, your sleep chronotype, the time of day you’re flying, and more. This means that generic advice to “get sunlight once you land” or “avoid napping at your destination” will not work for everyone—and can actually make jet lag worse if it shifts you in the wrong direction. Instead, you need to do the mental math of calculating what time your unique body thinks it is, what time it really is, and how to bring those two things closer together. To make this process easier, Lockley created Timeshifter—an app that uses circadian science to formulate individualized jet lag plans for travelers. After inputting information on your flight, preferred sleep timing, chronotype, and preferences such as supplement or caffeine use, the app tells you exactly when to sleep, nap, see some light (by going outside, turning on an overhead light, or using electronics), and keep things dark (by drawing the shades or wearing sunglasses). On average, Lockley says, those who follow the app’s advice are able to shift to the new time zone three to four times faster than they would normally. (If travelers can’t do everything perfectly, he says that following the plan as closely as you can will result in less jet lag than doing nothing.) These tools can also have multiple interacting benefits. For example, Lockley explains that caffeine use can not only keep you awake but help you to stay awake long enough to see light at the right time, while melatonin may help you sleep and shift the clock but also help you to avoid light at the right time (just be careful as it can disrupt your hormones and cause grogginess). As for the flight itself, drinking plenty of water, moving around and stretching if you can, and skipping the booze should all help make the experience a bit more pleasant and set you up for success upon landing. Emma received her B.A. in Environmental Science & Policy with a specialty in environmental communications from Duke University. In addition to penning over 1,000 mbg articles on topics from the water crisis in California to the rise of urban beekeeping, her work has appeared on Grist, Bloomberg News, Bustle, and Forbes. She’s spoken about the intersection of self-care and sustainability on podcasts and live events alongside environmental thought leaders like Marci Zaroff, Gay Browne, and Summer Rayne Oakes.
