Anyone who has ever flown is likely to have experienced some degree of time zone change disorder, commonly known as jet lag. Until recently, jet lag was not treated as a medical condition. It is now included as one of the 84 known or suspected sleep disorders and affects millions of people each year.
Jet lag occurs when the body's biological clock is out of sync with local time. When traveling to a new time zone, our bodies are slow to adjust and remain on their original biological schedule for several days. The result is that we feel excessively sleepy during the day or wide awake at night.
People may experience jet lag in varying degrees. In general, the severity of jet lag symptoms is directly related to the number of time zones crossed by a flight. Jet lag symptoms typically last longer following eastward flights. Flying east usually results in difficulty initiating sleep, where as flying west results in early morning awakenings. All age groups are susceptible, but individuals over the age of 50 are more likely to develop jet lag than those under the age of 30. Also, individual susceptibility tends to vary considerably and it is possible that pre-existing sleep deprivation will intensify jet lag.
Reviewed by Helen J. Burgess, Ph.D. on April 6, 2005