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In the study, National Institutes of Health (NIH) grantee Charles A. Czeisler, M.D., Ph.D. and colleagues at Harvard Medical School and Brigham and Women's Hospital in Boston studied 34 healthy older people, both men and women ranging in age from 65 to 81, and found that their nighttime melatonin levels did not differ significantly from those of 98 younger men whose age ranged from 18 to 30. The study, which spanned five years, appears in the November issue of the American Journal of Medicine.*
Study participants were medication free and did not have insomnia or other sleep complaints. They had to forego alcohol, caffeine, and nicotine and were also asked to keep a sleep journal. As part of their participation in the study, each person spent three days and three nights isolated under carefully controlled conditions in a sleep laboratory at Brigham and Women's Hospital. In order to minimize the effect of the experiment on their usual patterns of melatonin secretion, participants maintained their normal sleep schedules. At regular times, scientists took blood samples in order to assess melatonin production.
"In our analysis, we did not find any statistically significant difference in nighttime melatonin concentrations between the young and older subjects, although our study does not address whether melatonin levels change after the eighth decade," said Dr. Czeisler. "This means that in most healthy people, concentrations of melatonin in plasma probably do not decline with aging."
Melatonin is secreted by the pineal gland, which is located deep within the brain. The hormone may be a natural sleep inducer. It is produced at high levels during a person's normal sleeping hours and is low during the day. A number of factors, including light and many common medications, can affect melatonin secretion.
"The idea that a pineal aging clock winds down as you get older is simply not true," says Jamie M. Zeitzer, Ph.D., an author of the paper. "Being older does not cause a person to have low melatonin levels. While we know that some older individuals have low melatonin levels, it isn't because of their age per se."
"To say that aging affects the regulation of melatonin secretion is not borne out by the scientific literature, especially this newest study, the most comprehensive and carefully designed to date," says Andrew A. Monjan, Ph.D., M.P.H., Chief of the Neurobiology of Aging Branch of the NIA's Neuroscience and Neuropsychology of Aging Program. "It is important that people understand however that there is some preliminary evidence that melatonin may be useful for jet lag and some types of insomnia."
"Another thing not to overlook," explains Dr. Monjan, "is that commercially available melatonin remains un-standardized, unregulated, is largely untested, is expensive, and we still do not know how safe it is for long term use, especially for older people with a variety of health problems taking a number of drugs."
This study was supported by the NIA, NIMH, and NCRR, three components of the NIH. The NIA supports basic, clinical, epidemiological, and social research on aging and on the special needs of older people. The NIMH supports research on mental disorders, the brain, and behavior. NCRR funding provides highly specialized research resources to biomedical researchers nationwide, including the sleep laboratory at Brigham and Women's Hospital. The NIH is the leading Federal biomedical and behavioral research agency.