Amazing Places

Here's Why Jet Lag Is Worse When You Travel East

Jet lag is never fun, but it's not all equally unpleasant. Sometimes, it means a day or two of poor concentration and wonky sleep patterns; other times, the suffering lasts more than a week. The severity depends on how many time zones you cross — but according to research, it also depends on which direction you travel in

Related Video: Beat Jet Lag With Science

Why Jet Lag Happens

It seems obvious why jet lag happens: you flew to a new time zone and your body's adjusting! But on a cellular level, it's a complex phenomenon. See, when you arrive in a new time zone, the time change disrupts your body's circadian rhythm, or internal clock. Everyone has a slightly different internal clock — that's why some of us are night owls and others are morning larks. Everyone's circadian rhythm has its roots in a specific type of brain cell: the oscillatory pacemaker cells of the hypothalamus.

These cells play a key role in your daily functioning. By syncing up with each other and with external cues, like sunlight and alarm clocks, they keep you on a roughly 24-hour sleep cycle. When you travel, though, these cells get thrown out of whack. Suddenly, they're just synced with each other because your external cues are all over the place: sunrise is happening at a bizarre time, and you're eating dinner when you'd usually eat breakfast. Jet lag is the transition period when they sync themselves to their new environment.

This is a complex process, though, because not all of these cells are identical. They have different innate frequencies. Isolated from the sun and each other, some would set your sleep cycle to slightly shorter than 24 hours; others to longer. Overall, their average frequency is slightly longer than 24 hours — about 24.5 hours. This is why traveling east makes for worse jet lag than traveling west.

Go West, Young Man

See, when you fly westward, the day you arrive at your destination is longer than normal. You're basically racking up extra daylight as you fly. When you travel east, though, it works the opposite way — you lose daylight during your flight, and when you arrive, the sun sets earlier than your body expects.

Because your oscillatory pacemaker cells already tend toward a 24.5-hour sleep cycle, a longer day is easier for them to adjust to. A shorter day, on the other hand, rubs them the wrong way and causes more intense jet lag symptoms.

At least, this is what the researchers in this recent study in the journal Chaos found, using a somewhat simplified computer model of jet lag — or, as they call it, the pacemaker cells' "resynchronization" process. Their model doesn't capture every nuance of the human brain, but they argue that it has stronger predictive power than previous models and reveals something many of us have experienced but never named: the "the east/west jet-lag asymmetry," as they call it. (Sounds official, huh?)

The researchers hope that this finding is a small step towards vanquishing jet lag for good, but it's hard to put to pragmatic use — it's rarely up to you whether you travel east or west. Luckily, this military-tested jet lag diet can alleviate symptoms in a way this research can't yet; it basically lets you start resetting your circadian rhythms before you fly, so that by the time you land, you're adjusted to your time zone and ready to roll.

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If you want a time-tested cure for jet lag, try this 20-year bestseller: "The Cure for Jet Lag" by Lynne Waller Scanlon and Charles F. Ehret Ph.D. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Mae Rice December 7, 2018

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