Melatonin effects on body: More than a sleep hormone

Science-based article by: Inka Land, neuropsychology MSc

This article review the essential roles of melatonin in sleep and beyond.

Melatonin is most commonly known as a hormone of sleep and circadian rhythm. Melatonin supplements are widely used in treating insomnia and correcting jet lag. But to regard melatonin solely as a “sleep hormone” would be an understatement of its role in the human health and physiology. Melatonin has many roles beyond sleep; its upregulates cellular anti-aging pathways and immunity, protects the brain's longevity, supports neuroplasticity, and may protect mental health.

Table of contents

1. What is melatonin
2. Melatonin initate sleep
3. Melatonin supports immunity
4. Melatonin has anti-aging and neuroprotective benefits
5. Melatonin might improve mood
6. Melatonin is important anti-obesity and fat burning molecule

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What is melatonin

Melatonin (5 methoxy-N-acetyl tryptamine) a molecule widely distributed in nature. It’s functionally active in unicellular organisms, plants, fungi, and animals. It's the main hormone secreted by the pineal gland, a brain structure that Rene Descartes called the seat of the soul. Melatonin is often called the hormone of darkness because its levels are higher during the night and it has a critical role in sleep.

Human body naturally produces melatonin, but melatonin can also be made as a supplement synthetically or from animals or microorganics.

Melatonin as a sleep hormone

Melatonin is extremely beneficial for sleep health and maintaining circadian rhythm. Human brain produces melatonin in the evening, about 0.3–0.5 mg, which is enough to initiate sense of sleepiness and help to maintain sleep during the night.

Melatonin turnover and release is stimulated by darkness. Environmental darkness (sunset and dim environment) activates noradrenergic inputs to pineal gland, which signals it to produce melatonin. On the contrary, bight white and blue lights restrict the pineal gland from releasing melatonin which explains why it’s particularly important to have dim light conditions and block blue lights in the evening.

Melatonin supports immunity

Melatonin is also anti-inflammatory supplement. Its ability to fight against disease is due to its ability to fight free radical damage in the cells. Free radicals are placing the mitochondria under oxidative stress, which is one of the etiological determinants of significant diseases like inflammation, aging, and even cancers. Cells combat oxidative stress with antioxidants. Melatonin has established to be a potent scavenger of free radicals. It’s twice as effective as vitamin E, the most powerful lipophilic antioxidant. Melatonin signaling also indirectly promotes the expression of other antioxidant enzymes. Melatonin can also suppress tumor growth and protect against viruses.

Melatonin receptors are located in significant organs outside the nervous system (liver, kidney, skin, etc), which means it can systemically modulate the whole body's immune system.

Melatonin has anti-aging and neuroprotective benefits

Melatonin has been suggested to both improve neuroplasticity and protect the brain from aging. And there are multiple reasons for this. 

Melatonin can increase growth-related proteins like GH and IGF-1 and promote neurogenesis and cell migration in the brain. For example, IGF-1 stimulates protein synthesis in neurons, glia, oligodendrocytes, and Schwann cells and supports neuronal survival.

In an animal model of Alzheimer’s, melatonin supplementation protected against accumulation of amyloid beta and hyperphosphorylation of tau protein, cognitive impairment, brain oxidative stress, and a decrease in mitochondrial DNA. In other animal studies, it’s been demonstrated that melatonin supplementation reverse the reduction in neurogenesis in hippocampus, which is a crucial area for learning, memory, and mood in the human brain.

Can melatonin improve mood?

There has been a growing interest in using melatonin to counteract major mental health disorders like depression. One systematic review and meta-analysis from 2023 concluded that melatonin has consistently shown to reduce depressive symptoms, whereas a 2014 review did not find an effect.

So clearly, some studies support melatonin’s role in reducing major depression, whereas other studies yield no effects.

Along with these studies, a review from 2021 concluded that the clinical evidence for the use of melatonin for depression is contradictory. Still, melatonin might have a beneficial effect on mood, in some cases, because of it’s ability to support brain growth factors and hippocampal neurogenesis rather than combatting depression directly.

Melatonin is an anti-obesity and fat-burning molecule

Melatonin is vital for regulating metabolism and maintaining body weight. Long-lasting reduction in melatonin secretion is often associated with significant weight gain.

A systematic review concluded that melatonin is effective in reducing weight and visceral fat. Melatonin also appears to increase metabolism and protect muscle tissue.

In one study, postmenopausal women who supplemented melatonin for one year had their fat mass decreased by 7 %. 

The anti-obesity benefits of melatonin are associated with melatonin’s role in glycemic control, modulation of white fat tissue, lipid metabolism, and mitochondrial activity. Melatonin also increases brown adipose tissue volume and activity, which is the "good" fat that burns the harmful white fat. Weight loss benefits are also associated with melatonin’s anti-inflammatory and antioxidant abilities. 

How to naturally support melatonin?

Sunlight is one of the most potent regulators of melatonin because light waves directly stimulate the melatonin-producing pineal gland through the retina of the eye. As a rule of thumb, sunlight exposure (to eyes) in the early morning, during midday, and at sunset support the correct rhythmicity of pineal gland -produced hormones and melatonin synthesis.

Early morning sun exposure for 5-15 minutes activates a cascade of circadian hormones. During the midday, full-spectrum sunlight accumulates melatonin precursor hormone serotonin in the brain and increases sleep pressure. Later in the afternoon, sun stops emitting blue and bright lights and starts emitting predominantly red and infrared light that activates melatonin production. The final and most important signal for the pineal gland is darkness, which initiate a significant surge in melatonin production.

Summary

Melatonin is a hormone in the human body and a functional molecule virtually in most of the Eart biodiversity. Although melatonin is known as a human's sleep and circadian rhythm hormone, it also has a vital role in supporting human immunity, brain longevity, mood, neuroplasticity, fat burn, and healthy body weight. Environmental light is the most potent regulator of melatonin production in the brain’s pineal gland.

References

All references to PubMed articles are embedded in the text.