Melatonin 101: A Beginner’s Guide – Part 1

Melatonin is the only hormone whose production is stimulated by light. By the way, don’t confuse melatonin with the pigment found in the skin, melanin. Some people do confuse the two because the pigment melanin can also be stimulated by sunlight. 

Back to melatonin.

Melatonin is synthesized in the pineal gland from a pathway that includes the amino acid tryptophan→5-hydroxytryptophan (5-HTP)→serotonin→melatonin.(2) 5-HTP is sometimes clinically used to increase melatonin production. You may also recognize serotonin as the “happy hormone” that stabilizes mood and helps us maintain a more positive attitude and feelings of well-being.(3) 

Melatonin is best known as a sleep hormone. Its production and secretion are lowest during the daylight hours and highest when dark and play an important role in your sleep cycle. Melatonin secretion decreases with age and with some sleep disorders. Melatonin levels begin to increase about 2-3 hours before bedtime and are at a peak around 5 hours later.(4)

It has been successfully used to treat some sleep disorders, including:

• Insomnia in those with melatonin deficiency and generalized insomnia. Melatonin can be selectively used in those with delayed sleep-wake phase disorders. There is also a theoretical rationale for using melatonin in advanced sleep-wake phase disorders, though, to date, there have been no published clinical studies.
• Jet lag
• Shift work sleep disorders
• Some sleep disorders in children
• Circadian sleep disorders in blind individuals

Some of the effects of melatonin depend on its presence the night before and its absence during the daytime hours, these effects having been “primed” the night before. These are called prospective and proximal effects and include regulation of “clock genes” controlling circadian rhythms, reproductive hormone levels, and insulin-producing cells in the pancreas.(5) Melatonin can inhibit the release of both luteinizing hormone (LH) and follicle stimulating hormone (FSH) and therefore regulate testosterone, progesterone, and estrogen production.(6)

Other effects of melatonin are called “chronobiotic” effects because they serve to reset and synchronize various biological rhythms, apart from the sleep-wake cycle. These effects also are via the clock genes and can regulate and control biochemical events in the brain and tissues such as muscle, fat, pancreas, reproductive organs, adrenal glands, and liver. 

There are at least two sleep-wake phase disorders where the mistiming of melatonin release—either advanced (too early) or delayed (too late) melatonin release causes different forms of insomnia. (Melatonin, Part 2 will describe these in more detail)

Finally, melatonin has seasonal effects—in some animals, for example, melatonin helps regulate hibernation. In humans, as days become shorter and nights longer, the production of melatonin by the pineal gland reflects those changes in total daylight hours along with changes in, for example, how energy is metabolized. These seasonal effects can also impact the reproductive and immune systems and may be, at least in part, one of the causes of Seasonal Affective Disorder or the “winter blues”.(7)

To briefly review, melatonin has antioxidant and anti-inflammatory properties. It helps regulate sleep, energy metabolism, the production of insulin, affects organs like the liver, fat cells, bone tissue, the adrenal glands, and the production of reproductive hormones.