Why Is Jet Lag Worse After You've Traveled East?

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If there's one thing about traveling that's worse than long security checkpoint lines, it's jet lag. Arriving at your destination sleepy and physically drained can put a real damper on your trip. The frequent inability to sync up with local time for days after only prolongs the discomfort. CNN reports that a recent study by researchers at the University of Maryland published in the journal Chaos used mathematical models to explain why jet lag after a westward trip is not as intense as jet lag following an eastward trip.

Jet lag is, according to the article, a disruption of the brain's circadian clock, which is what allows organisms to coordinate biological functions (like sleep) with the environment as it shifts from day to night (or over the course of a typical 24-hour day). Cells in the hypothalamus known as pacemaker cells keep our bodies in rhythm. But when we move rapidly across numerous time zones, the cells are unable to quickly establish a new rhythm, so we feel groggy and out-of-whack while the cells work to catch up. 

Study co-author Michelle Girvan used an analogy of cars circling a race track to explain how the pacemaker cells work: Normally, the movement of the Sun acts as the "man with the yellow flag," indicating where the circular track's finish line is. This marker helps the pacemaker cells complete their circuit in correspondence with the environment. "In the absence of a controlling influence," Girvan explained, "the clump of [pacemaker] cells completes the circuit within a period of time that may not correspond exactly to one day."

With no man with the yellow flag to keep things on track, Girvan and her team's mathematical model showed that the average person's circadian rhythm slightly exceeds 24 hours by about 30 minutes. When traveling through time zones—particularly when traveling east, or "forward" in time—these extra half-hours compound.

As everyone's circadian clock is different, this also explains why jet lag hits some people harder than others. "Our model suggests that the difference between a person's natural period and 24 hours controls how they experience jet lag," Girvan said.

Besides vowing to only fly west for the rest of your life, you can take steps to adjust to a new time zone more quickly. Being outdoors where your body can be exposed to the day-to-night cycle is better than sitting in a dark hotel room, and finding a way to force yourself to be awake during the day and in bed at night could also help. You could also try taking a page from the NASA handbook: Astronauts go through sleep training and are taught to wear sunglasses on flights and to only take medications at a certain time of day to help their bodies adjust.

[h/t CNN]