Melatonin is the principal hormone of the vertebrate pineal gland, and it is also produced by extra-pineal tissues in amphibians. It is found in plants as well, but at much lower concentrations than in animals. This hormone is involved in setting the timing (entrainment) of mammalian circadian rhythms, as well as regulating seasonal responses to changes in day length in seasonally breeding mammals—so called photoperiodic responses. Photoperiodic responses include changes in reproductive status, behavior and body weight. Seasonal effects on reproduction in humans are subtle, and the role of melatonin here, if any, is unclear. Recently, melatonin supplementation has become popular as an aid for sleep disorders among other things.

How it works

Melatonin is synthesized by the pineal gland in the midbrain. The essential amino acid L-tryptophan is a precursor in the synthesis of melatonin. In this synthesis, L-tryptophan first gets metabolized to 5-hydroxytryptophan from which 5-hydroxytryptamine, also known as serotonin, is made. 5-hydroxytryptamine is converted to melatonin in a two-step process, occurring mainly in the pineal gland.

Melatonin promotes rapid eye movement (REM) sleep and circadian rhythms that regulates the metabolism of all higher organisms. In man, the body shifts into a quiescent state during sleep which facilitates cellular repair and rebuilding of body tissues. When awake the body operates its metabolism at a much higher rate than when sleeping. Blood pressure, heart rate, breathing, and brain activity operate at a much higher rate requiring most of the available energy of the body. This heightened activity leaves little energy for replenishing vital protein, nutritional, cellular repair, and hormone stores for vitality, down regulation of localized inflammatory states, muscle growth and cellular repair which are necessarily carried out during sleep. This is why sleep is so vital to the maintenance of good health.
During sleep the liver, kidneys, and other organs typically detoxify the accumulation of ingested, internally manufactured, and inhaled toxins. As heart rate slows and blood pressure drops during sleep, the pressure differential in the extra-cellular spaces allow the cells to expel toxins from the cytoplasm into the interstitial spaces where the lymph and venous systems pick them up and carry them to liver, kidneys and gut for elimination. When one dreams in what is called REM sleep, the body is actually in a paralytic state, unable to move. A great deal of emotional adjustment and brain repair is carried out in REM sleep.

Fitness/Sports Applications

One of the most important aspects of proper performance (and one of the least practiced) is the concept of regular sleep patterns. Athletes are notorious for working their bodies extremely hard, and not getting the required sleep they need for proper performance. This is seen in a multitude of high school athletes who never make it through intercollegiate sports, and college athletes who do not continue after university sports. Dancers, and some professional athletes who have hectic travel schedules, who disregard the importance of sleep also limit their longevity in their sports. REM sleep,