Causes of Jet Lag
A Hypothetical Case of Jet Lag
If a person flies across time zones, they cannot immediately resynchronize their biological clock with the new day and light cycle. The inability to adjust circadian rhythms during this "lag" time in synchronicity is called jet lag.
For example, a traveler bound for New York leaves Cairo, Egypt, at 6 a.m., travels eastbound for seven hours, and arrives in New York at 6 a.m., New York time. So, the traveler arrives at the "same time" that they left. However, according to the traveler's circadian rhythms and internal clock, it is 1 p.m., Cairo time, perhaps time to eat lunch, but not breakfast.
In 10 hours, when it's 4 p.m., New York time, the traveler's body feels like it is 11 p.m., Cairo time, and time to sleep. It's daylight in New York, where people are just beginning to think about dinner. The traveler's body thinks it should be dark. As soon as the traveler attempts to adjust to New York time by staying awake, circadian rhythms are disturbed, and complications arise.
For maximum efficiency, the body's 24-hour circadian rhythm cycle is intrinsically tuned to the light-dark cycle of the external environment.
The body coordinates its wake time with all the body functions that are best run at certain levels during certain hours of the day. However, this synchronization is slow to adapt to changes in external stimuli, like day-night times. One's ability to synchronize his or her biological clock with the external environment is limited. And a person can only change their clock by a couple of hours a day. Thus, complications like jet lag arise. A traveler changing seven time zones may need a week to adjust.
Some people have greater difficulty than others managing the circadian rhythm disturbance of jet lag. Severe cases may lead to more serious sleep disorders, such as delayed sleep-phase syndrome and advanced sleep-phase syndrome.