Circadian rhythm, travel fatigue, and jet lag.

When we hear the words "jet lag," we think of fatigue and sleep disruption, but jet lag entails the disruption of several physiological rhythms. It differs from travel fatigue. Travel fatigue is the result of experiencing the stress and hassles of travel and being in a cramped position (whether in a car, plane, or train) for several hours. Flying long distances from north to south (or vice versa) produces travel fatigue. Flying across several time zones (east-west or west-east) produces jet lag and travel fatigue. Jet lag is "a mismatch between 'body clock time' and the new local time," Thomas Reilly and colleagues explain in "Coping with Jet-Lag: A Position Statement for the European College of Sport Science" (European Journal of Sport Science. November 7, 2007).

Travel fatigue can be mitigated by doing everything possible to lessen stress. Make travel plans well in advance. Have all necessary documentation, inoculations, etc. Include a stopover to break up a long journey, if possible. To counteract dehydration caused by an airplane's dry air, Reilly et al. recommend eating apples or other foods high in roughage, drinking plenty of water or fruit juice, and avoiding tea, coffee, and alcohol. Travel fatigue is usually resolved by relaxing with a non-alcoholic drink or taking a shower and a brief nap, if needed, upon arrival at one's destination.

Relieving jet lag simply takes time, although Reilly and colleagues have a few suggestions for reducing symptoms. First, they do not recommend sleeping during a flight unless it is night at the final destination. In other words, start adapting to the new time zone during the flight. Body rhythms are primarily set by the natural cycle of light and darkness. When used at appropriate times, exercise or other activity in daylight and exogenous melatonin (to encourage sleep) promote resynchronization.

"We now know that nearly all biological functions display significant 24-hour rhythms," Bjorn Lemmer, MD, PhD, told attendees of the World Bank's International Travel Health Symposium in April 2000. Cortisol concentrations in human plasma, oral temperature, pulse rate, blood pressure, breathing, urine values, and serum measurements (e.g., protein concentration and electrolytes) have a rhythmic pattern, a rise and decline, during each day. The sleep-wake cycle can adjust to a journey across six time zones within a few days, but cortisol and body temperature cycles can take five to eight days. Traveling eastwards causes more severe symptoms than traveling westward. In general, resynchronization takes about one day for each time zone, but that can widely vary. Some people need 18 days to recover from a six-time-zone journey. Others need only two.

Lemmer B. Time Zone Travel and Peak Performance. (Presented at Stress, the Business Traveler and Corporate Health: An International Travel Health Symposium, April 27, 2000). Available at: www.hsd.worldbank.org/symposium/427-4-lemmer.htm. Accessed April 16, 2008.

Reilly T, Atkinson G, Edwards B, et al. Coping with jet-lag: A position statement for the European College of Sport Science. European Journal of Sport Science. March 2007;7(1): 1-7. Available at: www.ecss.de/images/PDFs/EJSS_PosStat_Vol7,lss1_2007.pdf. Accessed April 16, 2008.

Rosekind M. Jet Lag and the Business Traveler--Mood, Behavior and Work Functioning. (Presented at Stress, the Business Traveler and Corporate Health: An International Travel Health Symposium, April 27, 2000). Available at: www.hsd.worldbank.org/symposium/427-4-rosekind.htm. Accessed April 16, 2008.

briefed by Jule Klotter