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Most living things display changes in biochemistry,
physiology, and behavior that occur on a regular schedule every 24 hours or so.
This is known as our biological clock or circadian rhythm. The clock is "set" by
environmental cues, light being one of the most important.
As mentioned previously, melatonin secretion is promoted by
darkness and inhibited by light. Humans have a regular pattern of melatonin
secretion that corresponds with the 24 hour night and day cycle. Researchers
have found that humans will maintain a regular cycle of melatonin secretion even
in the absence of environmental light cues; however, the cycles are less precise
and may not follow a 24 hour schedule in the absence of external light cues
(when subjects are kept in continual darkness). This endogenous cycle of
melatonin secretion is the result of signals from the suprachiasmatic nucleus.
Although external light does not cause the 24 hour pattern, it does influence it
to be more precise.
Problems with 24 hour cycle of melatonin secretion occur when
traveling across time zones (jet lag), unusual work schedules, or blindness.
All of these conditions often result in sleep disturbances. Many studies have
been done to determine if ingestion of melatonin can help to relieve sleep
problems associated with these disturbances in the circadian rhythm. |
