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Causes
By Mayo Clinic staff
A disruption to your circadian rhythms
Jet lag can occur anytime you cross two or more time zones. Jet lag occurs because crossing multiple time zones puts your internal clock or circadian rhythms, which regulate your sleep-wake cycle, out of sync with the time in your new locale. For instance, you lose six hours on a typical New York to Paris flight. That means that if you leave New York at 4:00 p.m. on Tuesday, you arrive in Paris at 7:00 a.m. Wednesday. According to your internal clock, it's 1:00 in the morning, and you're ready for bed, just as Paris is waking up. And because it takes a few days for your body to adjust, your sleep-wake cycle, along with most other body functions, such as hunger and bowel habits, remains out of step with the rest of Paris.
The influence of sunlight
A key influence on your internal clock is sunlight. That's because the pineal gland, a part of the brain that influences circadian rhythms, responds to darkness and light. Certain cells in your retina — the tissue at the back of your eye — transmit the signal of light to an area of your hypothalamus, a part of your brain. The signal is then sent to your pineal gland. At night, the pineal gland releases the sleep-promoting hormone melatonin. During the day, melatonin production stops. So you may be able to ease your adjustment to your new time zone by exposing yourself to daylight in that new time zone.
Airline cabin pressure and atmosphere
Some research shows that the changes in cabin pressure associated with air travel may contribute to some symptoms of jet lag, regardless of travel across time zones. A July 2007 study published in the New England Journal of Medicine showed that simulated air travel at cabin pressures equivalent to 7,000 to 8,000 feet of elevation produced symptoms of altitude-related malaise (a feeling of unwellness), muscular discomfort and fatigue. In addition, most airline cabins circulate very dry air, which can be dehydrating. And mild dehydration can contribute to feelings of malaise, headache, and eye and nasal discomfort.
