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Help for Cuckoo Clocks
Ruth Levy Guyer, Ph.D.
A group of English police officers who do rotating "shift" work -- their schedules change every few weeks -- found that they were more alert, slept better and longer, and were in better moods if their bedtime beverage was the hormone melatonin (1).
A blind man who, for a decade, suffered from insomnia and daytime sleepiness, got his problems under control with nightly doses of melatonin (2).
And, a group of elderly insomniacs in Israel fell asleep more easily and slept better when they took a few milligrams of melatonin in the evenings (3).
What's so mellowing about melatonin?
Melatonin is a natural human hormone. It is released by the pineal gland in the center of the brain. The gland gets its name from its shape, which is like that of a tiny pine cone.
The level of melatonin in the body -- which is low during daytime and high at night -- is sensitive to light. When twilight falls, the pineal gland pours out melatonin; when daylight strikes the eyes at dawn, the melatonin spigot is turned off. Light's cues are picked up by the retinas, which serve as sensors -- photoreceptors -- in the eyes (4).
The body's pacemaker in the brain helps to regulate melatonin secretion. Each day, the pacemaker must reset the body's "biological clock," because the clock does not run automatically on a 24-hour cycle, yet people's lives do. The pacemaker and melatonin are in constant communication: signals from the pacemaker influence melatonin production, and melatonin production adjusts the pacemaker (5,6).
The release of melatonin fluctuates not only daily but also during an individual's lifetime. As people age, for example, their pineal glands produce less melatonin. All of the elderly subjects in the Israeli study had low levels of melatonin, but the insomniacs in the group had the lowest.
Studies with blind animals indicate that light signals are, indeed, critical for regulating the clock. But they do not work in isolation. In humans, social cues and other types of information in conjunction with light signals help establish the body's daily -- circadian -- rhythm. (The word circadian comes from two Latin words, circa, which means about, and dies, which means day.)
Although melatonin pills may help reset a range of incorrectly ticking biological clocks -- jet lag is another example (4) -- such pills are not expected to be cure-alls for every offbeat clock. For example, the doctors who conducted the Israeli study suspect that, although melatonin may be a useful substitute for counting sheep for elderly insomniacs, it will not help younger ones, whose sleep problems often stem from anxiety.
Photograph of an airplane taking off from the runway
Many studies of clocks, pacemakers, and circadian rhythms have been carried out in humans, but insights into what makes cells and organisms tick have come also from studies in plants and animals.
Biological clocks affect such diverse phenomena and processes as cell division, development of the organism, RNA metabolism, production of carbon dioxide by plants, and the activities of enzymes and hormones. Model systems are extremely valuable, because, with them, it is possible to make mutants, carry out genetic studies, do experiments in test tubes, and clone relevant genes.
Cells and organisms develop and function properly only when they've got their timing down. Then, in the best of circumstances, everything proceeds like clockwork.
References:
- Chronobiology International 1993, 10(5):315.
- Journal of Biological Rhythms 1991, 6(3):249.
- Health, October 1993, 18.
- Some background information in this article comes from an article by Jane Brody in the NY Times, December 29, 1993.
- Journal of Biological Rhythms 1993, 8(S):73.
- Annals of Medicine 1993, 25(4):303.
- Psychoneuroendocrinology 1993, 18(4):283.
This article was originally posted on the NIH electronic bulletin board EDNET on 3/15/94. |
