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 1999; Katz 2001; Lemmer 2002; Nicholson 1993; Waterhouse 2005b). Scientists have documented that even elite athletes' performance suffers from jet lag, and some world-travellers may experience depression after long flights (Boivin 2002; Cardinali 2002; Lemmer 2002; Reilly 2005).
Researchers have documented that jet lag affects 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 2000; Lemmer 2002; Tateishi 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 2000).
In addition, jet lag may trigger more serious conditions (Katz 2002). Researchers in Israel have investigated the relationship between jet lag and major psychiatric disorders. Conducted at a mental health center in Jerusalem, the study involved 152 patients who had been hospitalized for psychiatric disorders within a six-year period. Researchers assigned patients to one of two groups, based on the number of time zones they crossed while traveling to Israel. Only those patients who were mentally healthy at the time of travel or who had been free of any psychiatric symptoms for at least one year before travel were included in the study. The team documented a significant correlation between crossing seven or more time zones and a relapse of psychiatric disorders (Katz 2001, 2002).
Researchers in France have investigated whether chronic disruptions of the circadian rhythm could hasten cancer growth. Working with mice, they entrained one group to a normal rhythm of 12 hours' daylight followed by 12 hours of darkness. A second group of rodents repeatedly underwent 8-hour advances of the light-dark cycle every two days. Both groups were injected with cancerous cells known to cause tumors in mice. Compared with mice kept on a normal sleep-wake cycle, the jet-lagged mice experienced faster tumor growth (Filipski 2004).
Among humans, scientists have observed that frequently jet-lagged individuals and night-shift workers whose circadian cycles are routinely disrupted are more prone to disease than people who adhere to a normal sleep-wake cycle. Shift workers, for instance, are at increased risk of experiencing cardiovascular, gastrointestinal, and reproductive dysfunction, and are more prone to developing clinical depression (Burch 2005; Knutsson 2003; Moore-Ede 1985; Murata 1999; Reddy 2002, 2005; Scott 2000). There is also a correlation between sleep and proper immune function, so insomnia related to jet lag may increase susceptibility to infection (Bariga-Ibars 2005).