Light controls our circadian rhythm, the inner biological clock that tells us when to sleep and when to be awake. When we skip to a different time zone, our bodies no longer have the same light cues, and jet lag can turn an overseas jaunt into a nightmare of groggy days and alert, sleepless nights. But, with the right amount of light exposure, your body can adjust more quickly, and University of Michigan mathematicians have figured out how to calculate exactly how much light you need to beat back jet lag as quickly as possible.
The researchers, Danny Forger and Olivia Walch, have created an iOS app called Entrain, which allows users to input details of their trip, including duration, time zone, and how much light they can reasonably expect to be exposed to over the course of their journey. The app then comes up with a customised schedule for the user, showing when the traveler needs to spend time exposed to bright light or in dark, dim environments.
Think about flying from the East Coast of the U.S. to Japan, says Dr. Elizabeth Klerman, a sleep medicine and disorder researcher at Harvard Medical School. You can fly through each time zone one by one and have your circadian clock slowly adjust, or you can do what airplanes do.
"They basically fly up to the North Pole and skip across multiple time zones and then go back down again rather than having to cross each intermediate time zone," Klerman, who wasn't involved in the study, says. "Well, the equations that Forger used are able help you skip across time zones."
The app is free to use, but staying on its schedule might require some small additional investments. If you have to be outside in the sun when Entrain tells you you need to be in low light, pink-tinted glasses could help you adjust faster. A therapeutic light (like the kind used to treat seasonal affective disorder) could help when you need light at night.