Working with genetic and environmental influences on the body's internal clock, the hormone melatonin regulates daily biological functions of sleep, immune function and metabolism. According to a rat study published in "Endocrinology" in December 2003, surgical removal of the gland that secretes melatonin caused weight gain. Overweight rats receiving melatonin supplementation lost weight without changes to food consumption.
In response to signals from the brain's control center for the body's internal clock, the pineal gland makes and releases melatonin. Melatonin secretion is higher at night because light inhibits melatonin release. Melatonin secretion also varies with age. According to the "Journal of Clinical Pharmacology," a rapid decline in melatonin synthesis occurs between the ages of 6 and 20, then stabilizes between the ages of 20 and 40 and slowly declines after age 40.
Melatonin influences the body's daily cycles including sleep, body temperature and metabolism through feedback communication between the brain and hormone producing glands. In addition, a review of research published in "Sports Medicine," in 2003 indicates melatonin affects kdiney function to maintain water balance.
The body breaks down food into fats, carbohydrates and other nutrients for cell growth, repair and energy. Biochemical reactions convert excess carbohydrates into glycogen for storage in liver and muscles. When the blood glucose level decreases, the body uses stored glycogen for energy. According to a rat study published in "Life Science" in January 2000, test subjects on melatonin used carbohydrates and fats in the diet better for energy and preserved glycogen storage.
Healthy weight management requires a balance between calories eaten and energy used by the body. The "Endocrinology" study showed melatonin administered to rats on a high-fat diet decreased the development of fat tissue. Melatonin also reduced hyperglycemia and elevated insulin levels in the blood, risk factors for diabetes associated with obesity. A daily dose of melatonin one hour before lights-out was most effective for weight loss and resulted in lower blood levels of leptin the hormone influencing the storage of body fat.
The effect of melatonin lasts for a short time. According to a study published in "Journal of Clinical Pharmacology" in February 2008, biochemical reactions in the liver remove 99 percent of the melatonin five hours after administration. Timing of supplementation may affect how well melatonin works. The "Endocrinology" study showed body weight decreased by 5.1 percent with administration one hour before dark and no significant change in body weight if melatonin was given four hours after daylight in rats.
Melatonin may reverse the effect of decreased physical activity and age on metabolism. The "Sports Medicine" review reports that a significant reduction in the body temperature observed with higher melatonin levels in younger women was not observed in post-menopausal women. The "Endocrinology" study showed rats receiving melatonin decreased brown-fat deposits consistent with thermal response for reducing body fat.