Almost everyone who has traveled across more than a few times zones in one trip has experienced the debilitating effects of jet lag. While travel across vast distances is now rapid, convenient, and commonplace, we are still saddled with biological limitations arising from millions of years of evolution. The distress associated with jet lag results when the body’s internal clock, or circadian rhythm, becomes desynchronized with the external time zone.
Jet lag is characterized by unpleasant symptoms, including insomnia, sleepiness, impaired performance, diminished alertness, irritability, depressed mood, and gastrointestinal distress (Waterhouse J et al 2005). The symptoms of jet lag are slightly more dramatic for travelers heading east. In addition, older individuals are likely to suffer more from its effects (Monk TH 2005).
The human circadian rhythm—characterized by rising and falling hormone levels, undulating body temperature, and the familiar sleep-wake cycle—is linked to the rising and setting of the sun. Through its production of melatonin, the circadian hormone, the pineal gland plays a crucial role in the circadian rhythm.
Research suggests that the jet aircraft environment itself may also contribute to jet lag. In a recent experiment, researchers simulated the mild oxygen deprivation, or hypoxia, that occurs in pressurized aircraft cabins during long-duration flights at altitudes between 8000 and 12,000 feet. Participants were assessed for changes in melatonin levels. Scientists found a significant decrease in the nightly peak of melatonin, prompting speculation that hypoxia induced by cabin air contributes to post-flight fatigue after long flights and to the clinical disorder of jet lag (Coste O et al 2004).
Jet Lag’s Effects on the Mind and Body
Symptoms of jet lag may include malaise, decreased strength and efficiency, decreased ability to remember or concentrate, gastrointestinal disturbance, headache, irritability, loss of appetite, tiredness during the day, and sleeplessness at night (Committee to Advise on Tropical Medicine and Travel 2003; Haimov I et al 1999; Katz G et al 2001; Lemmer B et al 2002; Nicholson AN et al 1993; Waterhouse J et al 2005b). Scientists have documented that even elite athletes’ performance suffers from jet lag, and some globetrotters may experience depression after long flights (Boivin DB et al 2002; Cardinali DP et al 2002; Lemmer B et al 2002; Reilly T et al 2005).
Researchers have documented that jet lag affects the normal daily changes in blood pressure and heart rate, alters otherwise normal changes in body temperature, and disrupts the normal ebb and flow of the stress hormone, cortisol. These alterations in normal functions may last for a week or more (Cho K et al 2000; Lemmer B et al 2002; Tateishi O et al 2002). For instance, long-distance flight crews experiencing chronic jet lag, may have significantly elevated cortisol levels compared to those of controls. This elevation in cortisol correlates with deficits in cognitive performance (Cho K et al 2000)
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