The primary motivation for the use of melatonin as a supplement is as a natural aid to better sleep, with other incidental benefits to health and well-being due to its role as an antioxidant and its stimulation of the immune system and several components of the endocrine system.
Victor Herbert, M.D., J.D., of the Mt. Sinai School of Medicine, cites studies from Massachusetts Institute of Technology that say melatonin pills sold as supplements contain three to 10 times the amount needed to produce the desirable physiologic nocturnal blood melatonin level for enhancement of nighttime rest. Dosages are designed to raise melatonin levels for several hours to enhance quality of sleep, but some studies suggest that smaller doses are just as effective at improving sleep quality.
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A number of studies indicate melatonin supplementation helps to reduce the age-related decline in hormone production from the thyroid and pituitary glands, among others, with animal models suggesting these effects are associated with an overall enhancement of health
Melatonin is involved in the regulation of body weight, and may be helpful in treating
obesity (especially when combined with calcium)