What causes jet lag?

If you’ve ever suffered from jet lag you’ll know about it, as the thrill of arrival at your final destination is tainted by symptoms ranging from a very obvious fatigue and disruption of sleep patterns, to slight nausea, headache, disorientation, feeling groggy, irritable and even mildly depressed. Some people seem to be able to fly long distances and not feel too bad, while others can’t settle down in their new environment for a number of days.

So what causes all this? One of the reasons for jet lag is that your Circadian rhythm has been disrupted. This is your natural bodily rhythm that attunes itself to day and night, light and dark, making you wake up at a certain time in the morning, and start to feel sleepy in the evening. Anyway, when you travel across a number of time zones, your body clock is out of synchrony with the time at your destination, so that when you finally arrive your Circadian rhythm is most likely still working according to the time at the place you departed from, not according to your place of arrival.

So if you do get jet lag, how long will it last? A good rule of thumb is that it will last approximately one day for each time zone crossed, so if you fly from the UK to Japan, you might expect to have your Circadian rhythm disrupted for around nine days, whereas if you flew from London to New York, you might only feel this sense of disruption for five days.

But there is one odd quirk, it is said that jet lag is worse when you fly from west to east, rather than the other way round.

In my next post, I will talk about some ways of alleviating jet lag.