What causes the condition that affects most long-distance travellers?
We’ve all experienced it – that exhausted, sleepless, irritable feeling that results when your body is forced to reset its internal rhythms after a long-haul flight.
But what exactly is jet lag? Also known as desynchronosis, it can cause insomnia, daytime sleepiness, loss of concentration and alertness, fatigue, irritability, disorientation, depression and gastrointestinal problems.
And there’s seemingly no escape. One study found that 94 percent of Americans who flew long distances suffered from jet lag, and 45 percent described their symptoms as severe.
There’s growing evidence that jet lag may even harm your health, particularly as you get older. Another study found that while younger mice were able to rebound from the effects of air travel, being subjected to the equivalent of a Washington-to-Paris flight each week increased the death rate among older rodents.
So what causes jet lag, and why does it makes us so miserable. We have groups of interacting molecules in cells throughout our body that act as biological clocks, telling our glands when to release hormones and adjusting our body temperature and other variables.
The body’s tiny biological clocks follow a master timepiece – 20,000 nerve cells called the suprachiasmatic nucleus, or SCN, located in the brain.
The SCN keeps your body operating on a regular pattern of sleep-wake cycles and body functions known as a circadian rhythm. When it’s time to get some sleep, for example, the natural time-keeping system releases a hormone called melatonin.
The SCN knows when it’s a good time to do this because it’s located conveniently close to the optic nerves, which relay the perception of light from the eyes to the brain. Basically, when there’s less light, the SCN tells you to go to sleep.
The body likes regularity, so this natural clock gets accustomed to going off at the same time every night but when you cross multiple time zones, you get all messed up as a result.
The problem is at its worst when you fly eastward, for example, from the US to Europe. When it’s night-time at your destination, your body still thinks it’s late afternoon. You may wind up lying sleepless in your hotel bed all night, and finally doze off just when it’s time to get up.
You feel rotten because it causes the release of stress hormones, which make you feel anxious and grumpy. It drives up your blood pressure, while the shift also disrupts the release of appetite-regulating hormones, so that you get a craving to eat a lot of food at a time when you normally don’t eat at all.