Jet lag? There's an app for that

Researchers have found that evading jet lag may be as simple as carefully controlled periods of light exposure to keep circadian rhythms in check.

Whether you're travelling for business or pleasure, jet lag can cause a serious crimp in your plans, knocking you out with tiredness when you want to be awake and keeping you wide awake when you want to be asleep — and, for those who travel a lot, it can cause depression.

But a new app developed by researchers at the University of Michigan could seriously speed up the recovery time.

Jet lag is caused when the body's circadian rhythm becomes out of sync with the time zone. By carefully exposing the jet lag sufferer to certain types of light during certain times of the day, the jet lag recovery time can be cut right down.

"Overcoming jet lag is fundamentally a maths problem and we've calculated the optimal way of doing it," said Danny Forger, a professor of mathematics at the University of Michigan College of Literature, Science, and the Arts. "We're certainly not the first people to offer advice about this, but our predictions show the best and quickest ways to adjust across time zones."

The app, called Entrain, is based on entrainment, or realigning the circadian rhythm with the time of day. Forger and Yale doctoral student Kirill Serkh worked on the idea that light is the strongest signal to regulate circadian rhythms.

It involves creating a schedule where the sufferer seeks certain types of light for a block of time each day. For one block of time, they are to spend time in bright, outdoors-style light, such as a therapeutic lightbox, and for the second block of time, the dimmest light possible. You do not have to be asleep during this time, and you can block out blue wavelength light — the type of light most associated with daylight — by wearing pink-tinted glasses.

The user will need to enter a few details into the app — such as the typical hours of light and darkness in their "home" timezone, where they are travelling to and for how long, as well as the brightest light they expect to spend the most time in. The app will then calculate a plan for your light exposure and how long it ought to take you to readjust.

The researchers illustrate this with a circle representing the circadian rhythm, with the central point being the time of day when your body is at its lowest temperature, around two hours before you wake up. When you have jet lag, that time changes drastically — you could be at your lowest temperature at 3pm.

"The way other approaches get these points to line up again is by inching along on the outside of the circle, sometimes pushing you towards and sometimes pulling you away from the target. But our schedules can just cut through the middle," said Olivia Walch, a mathematics doctoral student who built the app. "This is almost like a body hack to get yourself entrained faster."

The full study can be read online in the journal PLOS Computational Biology. Entrain is available for free from the iTunes app store.