jet lag - Causes

Unpleasant mental and bodily sensations of fatigue, inability to concentrate, and impaired judgment, induced by rapid air travel through several time-zones. The condition is due to a disturbance in biological circadian rhythms, and usually subsides within a few days.

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Jet lag
Classifications and external resources

ICD-10	G47.2
ICD-9	307.45, 780.50

Jet lag, also jetlag or jet-lag, is a physiological condition which is a consequence of alterations to the circadian rhythm. Such alterations result from shift work, daylight saving time, altered day length, or as the name implies, transmeridian travel as on a jet plane. They are known as desynchronosis, dysrhythmia, dyschrony, jet lag, or jet syndrome.

The condition of jet lag generally lasts a few days or more, and medical experts have deemed that a recovery rate of "one day per time zone" is a fair guideline. Good sleep hygiene promotes rapid recovery from jet lag: in fact sleep, relaxation, moderate exercise, and sensible diet seem to be the simplest recovery methods.

However, since the experience of jet lag varies among different individuals, it is difficult to assess the efficacy of any single remedy.

Causes

When traveling across a number of time zones, the body clock goes out of sync with the destination time, and so it experiences daylight and darkness contrary to the rhythms to which it has grown accustomed.

Jet lag occurs because the body cannot automatically realign these rhythms.

The symptoms of jet lag can be quite varied, though on the whole, an individual may experience the following:

Dehydration and loss of appetite Headaches and/or sinus irritation Fatigue Disorientation and/or grogginess Nausea and/or upset stomach Insomnia and/or highly irregular sleep patterns Irritability, Irrationality

Dr Neil Stanley, past chairman of the British Sleep Society, sounded (4/2006) a note of warning over jet lag due to large time differences. He said:

If you are frequently changing time zone or working long hours or shifts, you do start working at only 60 to 70% of your potential. You lose concentration, you lose judgement, you lose reaction so [e.g.] as a politician you are not going to be on top of your game, to be honest.

The maximum jet lag a person can experience is 12 hours. The person will incur the same amount of jet lag as someone traveling between London and Los Angeles, where the actual time difference is 8 hours. Hence a ten-hour flight between Frankfurt and Johannesburg (going south, staying roughly on the same meridian) is less inducive of jet lag than a five-hour flight between New York and Los Angeles (going west). Note though, that the difference between the two directions decreases as the destination approaches the other side of the Earth (eg from the UK to New Zealand), which 'reverses day and night': while there is a big difference between a -6 and a +6 hours jet lag, there is a relatively small difference between -11 and +11 hours.

Although technically incorrect, the term "jet lag" is sometimes used in conversation to describe the general exhaustion of traveling, even if there is no change in time zone.