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Why Is Jet Lag Worse When Traveling East?

Jet lag hits harder when flying east because our circadian rhythms find it tougher to advance than to delay, akin to the challenge of falling asleep earlier rather than later. This disrupts our internal clock more severely. Ever wondered how this affects your body during those long-haul flights? Join us as we unravel the science behind your travel fatigue.

The human body is set in its ways. It knows when you need to eat, sleep, and take care of routine bodily functions. These essential daily activities are synced with your internal clock and its circadian rhythms. When you fly, however, the human body can get thrown for a loop, resulting in jet lag. Travel a relatively short distance and you’ll be fine, but cross two or more time zones and you can experience some pretty unpleasant consequences, from sleep problems and daytime fatigue to digestive woes.

Research published in a 2016 edition of the journal Chaos found that jet lag symptoms are worse the farther you travel. Perhaps this isn't surprising, as you're crossing numerous time zones, but the researchers also found that jet lag tends to be worse when you travel east and a little easier when you travel west. It can take more than four days to recover from eastward travel across three time zones. When traveling west across the same number of time zones, they found, your recovery time can be less than three days.

Why so tired?

  • The reason lies in the body’s ability to “phase advance” its bedtime and wake-up time to earlier in the day, as opposed to its ability to “phase delay” its bedtime and wake-up time later.

  • Sunlight has a big influence on circadian rhythms. Light affects the regulation of melatonin, a hormone that helps cells work together. When light levels are low, the hypothalamus triggers melatonin release. During daylight hours, the opposite occurs.

  • Airliner cabin pressure and high altitudes may also cause similar symptoms, regardless of the number of time zones that have been crossed. Low humidity in planes can also trigger some degree of dehydration, which can look similar to jet lag symptoms.

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    • Complete recovery from jet lag after eastward travel across three time zones takes over four days, while recovery from a westward trip across the same number of time zones takes under three days.
      By: Pavel Losevsky
      Complete recovery from jet lag after eastward travel across three time zones takes over four days, while recovery from a westward trip across the same number of time zones takes under three days.