Causes of jet lag 

Jet lag occurs when the body's normal daily routine is disrupted after crossing several time zones.

Symptoms such as sleep disruption and tiredness are the result of your body finding it difficult to adjust to your new location's time zone.

Circadian rhythm

Circadian rhythm is your body's natural 24-hour routine, which is controlled by "biological clocks" in your body. Jet lag occurs when your body's circadian rhythm is disrupted.

The biological clocks are found throughout your body and are made up of groups of cells that interact with each other. The cells are controlled by a "master clock" in your brain that keeps all the body clocks synchronised.

Your body is used to a regular routine of light and darkness at certain times of the day. However, when you travel to a new time zone, this routine is disrupted.

Air travel makes it possible to cross several different time zones in just a few hours. After travelling so quickly, your body has to catch up and re-establish its circadian rhythm. It takes time for your body to adjust to new times of light, darkness and eating. It may also have to adjust to temperature differences.

East and west

Symptoms of jet lag are usually more severe when travelling east. This is because your body finds it easier to adapt to a longer day (you "gain time" travelling west) than a shorter one (you "lose time" travelling east).

Your body is able to adapt better when you travel west because you're extending your day rather than shortening it when you travel east. It's usually easier to delay sleep for a few hours than trying to force sleep when you're not ready to.

Other risk factors

Other factors that can increase your risk of getting jet lag or its severity include:

  • dehydration (not drinking enough water)  
  • drinking alcohol and caffeine during the flight
  • a lack of sleep
  • stress 
  • being over 60 years of age

It's also thought that high altitude and changes in cabin pressure may lead to some of the symptoms of jet lag, regardless of travel across time zones.

Sleep routine

If you stick to a strict sleep routine, such as going to bed at the same time each night, you're more likely to be affected by jet lag.

Babies and children can sleep at any time of the day, so they tend to adjust to new time zones more easily and are less likely to experience jet lag.

Page last reviewed: 06/05/2014

Next review due: 06/05/2016