Jet Lag Explained

Jet LagWhat is “jet lag” and why do most people feel worse when they travel around the globe in one direction, rather than the other? An article in the journal Chaos, summarized in the New York Times, suggests an answer. And offers some hope that you can reduce the severity and duration of the symptoms.

For people with mood disorders, this may be especially important, because they may be more vulnerable to disruptions in their daily rhythms, and may be more likely to experience a mood episode (depression or mania) when travelling.

Normal circadian rhythms (daily rhythms of sleep and activity and fluctuations in the release of hormones that help regulate this) are regulated by roughly 20,000 cells located in the suprachiasmatic nucleus: a small area in the brain that is right next to the nerve tracts that carry signals from the eye back to the visual cortex. These cells have a regular pattern of activity that take place roughly every 24 hours.

These clock cells are not very accurate, on average they lose several minutes every day (they think that days are a little bit longer than 24 hours), but this is not a problem when people get adequate bright light exposure early in the morning (the bright light “resets” the clocks and keeps them all synchronized).

Researchers at the Institute for Research in Electronics and Applied Physics of the University of Maryland have modelled how these clocks work. They used the data from previous experiments on cells in the suprachiasmatic nucleus to create this computer model. Their model predicts several curious features of jet lag. One of these is that travel is much more disruptive when flying from west to east (going east). This fits with many other studies, as well as data from a couple of studies showing that psychiatric “episodes” are more likely to occur when travelers land at an airport after flying east.

Their model also highlights the importance of the timing of bright light exposure in getting back on a normal rhythm. Bright light exposure is not just a matter of getting out in the morning after you land, experts have created two “calculators” that can help you adjust to jet lag faster. One of these is available for free from British Airways (see below).

Another jet lag calculator was recently released as an iPhone app and was described in a recent Los Angeles Times article…

A research team from the University of Michigan and Yale University has released a free iPhone app that loads a complex, jet-lag conquering model right into your smartphone. You type in your current location and destination as well as what kind of light you will have access to, and the app gives you a schedule of light exposure that should reset your internal clock in the most efficient way.

“These are the fastest schedules that have ever been proposed,” said Olivia Walch, a PhD student at the University of Michigan who designed the app, called Entrain. “Our schedule takes what could be 12 days of adjusting down to four.”

Entrainment is the scientific term for fully adjusting to a new time zone — hence the app’s name.

The mathematical model was created by Daniel Forger, a biological mathematician who has been studying circadian clocks since the 1990s. A paper describing his research was published Thursday in the journal PLOS Computational Biology. The Entrain app was released the same day.

For More Information

Travel and Mood


British Airways’ Jet Lag Advisor


Resynchronization of circadian oscillators and the east-west asymmetry of jet-lag
Lu, Zhixin and Klein-Cardeña, Kevin and Lee, Steven and Antonsen, Thomas M. and Girvan, Michelle and Ott, Edward, Chaos, 26, 094811 (2016), DOI:

“Why Jet Lag Can Feel Worse When You Travel from West to East” by Joanna Klein. New York Times. July 15, 2016.

“A New Mathematical Model Can Cut Jet Lag in Half” by Deborah Netburn. Los Angeles Times. April 11, 2014.