Jet lag is a feeling of apathy and fatigue and other symptoms, caused by traveling in a jet airplane through several time zones. It occurs because of a disruption in a person’s biological clock. The biological clock , also called the circadian clock, is a timing mechanism that operates in living things. In humans, the circadian clock is responsible for synchronizing body functions that vary with the daily passage of time. It is in a part of the brain called the hypothalamus , which regulates such involuntary body processes as breathing, blood pressure, and heart rate. The biological clock coordinates the varied parts of the brain that control such things as sleep, alertness, memory, eating, and mood.
Regular exposure to bright light keeps the human circadian clock aligned with the time of the outside world. But the clock can be disrupted when people travel long distances in an airplane, rapidly crossing multiple time zones. When this happens, the internal clock may be unable to remain synchronized with the outside world. The result is jet lag. Jet lag can have many symptoms. They include tiredness during the day, insomnia (difficulty sleeping), indigestion , depressed mood, and reduced cognitive (mental) performance.
Jet travel is often associated with dehydration, anxiety, loss of sleep, changes in diet, and reduced activity. These symptoms arise primarily from extended time spent traveling in cramped airplanes. They can make the symptoms of jet lag worse. For example, changes in diet can worsen the indigestion arising from mistimed meals. Long flights often disrupt sleep patterns. Some people may nap during a daytime flight or be unable to sleep during an overnight flight. These factors can worsen any nighttime insomnia and daytime tiredness. During jet lag, the body’s circadian clock is often signaling sleep during the daytime and waking at night.
Jet lag may be overcome through exposure to sunlight in the new time zone as soon as possible upon arrival. People suffering jet lag should also drink fluids to stay hydrated, get a good amount of sleep at night, and eat as close to a normal diet as possible. For most people, jet lag will disappear without any treatment, as a person’s circadian clock adjusts to the new time zone. In general, it takes about one day to adjust for each time zone crossed. For a person flying from Los Angeles, California, to Paris, France, for example, a difference of nine hours, it would take up to nine days to completely adjust to the new time zone.
