What Is Melatonin and How Does It Affect Our Health?

The molecule of darkness. The hormone of rest and rejuvenation. The ultimate multitasker. These are just some of the ways nutrition scientist Deanna Minich, PhD, CNS, IFMCP, describes melatonin.

“When most people think of melatonin, they think of sleep,” says Minich. “They are unaware of its many other functions.”

Melatonin is a crucial part of the sleep cycle, but its role does not end there, she notes. “It’s a potent antioxidant, it regulates the mitochondria, it can stimulate the immune system, and it’s a circadian signal.”

And there’s more. Melatonin helps control temperature, blood pressure, and the gut microbiome. It also supports neurogenesis and protects nerve cells, which help repair and detoxify the brain.

“Melatonin is called nature’s most versatile biological signal,” Minich says.

Melatonin is a hormone found throughout nature, made by plants, animals, fungi, and even bacteria. In humans, most circulating melatonin is produced in the pineal gland from the amino acid tryptophan. The pineal gland responds to evening darkness by releasing melatonin into the bloodstream, telling the body it’s time for sleep.

On average, the pineal gland generates between 0.1 and 0.9 milligrams of melatonin per day. The gut mucosa contains about 400 times more, but most of it stays within the gastrointestinal tract. There it helps protect the gut lining, reduce inflammation, and regulate gut motility and the microbiome.

Melatonin is also synthesized in the eyes, skin, and various other glands and organs. At these sites, it helps modulate the immune system, repair tissue, and prevent oxidative stress and inflammation.

Our bodies start producing melatonin when we’re about 3 months old, with levels ramping up from infancy to adolescence and peaking ­before puberty. Production then declines and can drop significantly by the time we reach our 50s.

“This is when we find ourselves in ‘melatonipause’ — a term I love because it syncs up with the decline of so many other hormones,” Minich says.

In addition to aging, melatonin production is influenced by illness, diet, and environmental factors such as exposure to artificial blue light at night. Some medications and a lack of exposure to sunlight can also impact levels.