Causes
To understand jet lag, we need to know about circadian rhythms.
What are circadian rhythms?
Circadian rhythms, or the body clock, are 24-hour cycles in the biochemical, physiological, and behavioral processes of our bodies. They regulate daily activities, such as sleep, waking, eating, and body temperature regulation.
The body clock and the brain
Jet lag appears to involve a disruption in two separate but linked groups of neurons in the brain. These neurons are part of a structure called the suprachiasmatic nucleus (SCN). The SCN is located below the hypothalamus at the base of the brain.
One of these groups of neurons is associated with deep sleep and the effects of physical fatigue. The other group controls the dream state of rapid eye movement (REM) sleep.
The group of neurons involved in REM sleep finds it harder to adjust to the new cycle, and the two groups become out of sync.
What puts the body clock out of synch?
The body clock is driven by an internal time-keeping system, but it is affected by external environmental factors, such as the light-dark cycle of night and day.
When the body clock gets out of synch and needs to be reset, jet lag results.
Traveling across different time zones and going through daylight and darkness cycles that are different from the rhythms we are used to can cause our body clock to get out of synch. Other causes include shift work and some sleeping disorders.
Jet lag affects patterns of sleeping and waking and of eating and working.
Hormone regulation is key to body clock synchronization. When jet lag happens, hormone levels get out of sync with the environment. Body temperature also varies according to the body clock.
Jet lag will continue until all these factors can respond properly to the new environment.