Jet lag

Jet lag, also jetlag or jet-lag, medically referred to as "desynchronosis" is a physiological condition which is a consequence of alterations to circadian rhythms; it is classified as one of the circadian rhythm sleep disorders. Jet lag results from rapid long-distance transmeridian (east-west or west-east) travel, as on a jet plane.

The condition of jet lag may last many days, and recovery rates of 1 day per eastward time zone or 1 day per 1.5 westward time zones are mentioned as fair guidelines.

Cause

When traveling across a number of time zones, the body clock will be out of synchronisation with the destination time, as it experiences daylight and darkness contrary to the rhythms to which it has grown accustomed: the body's natural pattern is upset, as the rhythms that dictate times for eating, sleeping, hormone regulation and body temperature variations no longer correspond to the environment nor to each other in some cases. To the degree that the body cannot immediately realign these rhythms, it is jet lagged.

The speed at which the body adjusts to the new schedule depends on the individual; some people may require several days to adjust to a new time zone, while others experience little disruption. Crossing one or two time zones does not typically cause jet lag.

The condition is not linked to the length of flight, but to the transmeridian (east-west) distance traveled. A ten-hour flight from Europe to southern Africa does not cause jet lag, as travel is primarily north-south. A five hour flight from the west to the east coast of the United States may well result in jet lag.

Crossing the International Date Line does not contribute to jet lag, as the guide for calculating jet lag is the number of time zones crossed, and the maximum possible disruption is plus or minus fourteen hours.

Symptoms

The symptoms of jet lag can be quite varied, depending on the amount of time zone alteration. They may include the following:

* Digestive problems
* Headache
* Fatigue, irregular sleep patterns, temporary insomnia
* Disorientation, grogginess, irritability
* Mild depression

Other symptoms which some may attribute to jet lag, such as nausea, ear aches and swollen feet, may be caused by the mode of travel rather than the time zone change.

From http://en.wikipedia.org/