Did you know that melatonin is widely distributed throughout your body and is a naturally occurring substance that we all produce?

Melatonin is widely regarded as an important hormone that helps regulate and synchronize sleep rhythm, including sleep-wake timing [1] and seasonal rhythmicity aspects across vertebrates. It also has lesser-known (but very important) roles as an antioxidant [2]. We have touched briefly on melatonin in a previous article about sleep hormones and their effect on the GABA system here.

Sleep is of fundamental importance for anabolic processes that repair and rejuvenate the body overnight. It has also been described as neuroprotective, whereby the brain cleanses itself of damaging free radicals and reorganizes itself. If sleep is impaired, as it is in conditions such as insomnia, this process cannot optimally take place, leading to negative changes in cognition, behavior, and judgement [3]. Research in rodents has shown that sleep depletion causes cellular damage that can potentially lead to errors in replication and metabolic abnormalities [4]. For more information on why we sleep, you can read here.

Insomnia is a condition that affects around 30% of the population to some degree, and there seems to be consensus across nations for this percentage [5,6]. In brief, insomnia describes difficulty in getting to sleep, staying asleep, and achieving restful sleep. It is associated with co-morbidities such as diabetes, and therefore represents a significant public health challenge [7].

Perhaps as a consequence of these changes in sleep quality, especially in developed nations, melatonin has been used as supplement for many decades to promote better and more restorative sleep.

In this article, we will investigate melatonin and its functions, the rationale for supplementation, as well as possible risks and contraindications for its use.

What is Melatonin and How Does it Work?

Melatonin, or 5-methoxy-N-acetyltryptamine, is secreted from the pineal gland deep within the brain [8]. It was originally discovered and isolated from the pineal glands of cows in 1958 by Aaron Lerner [9].

It is mainly synthesized by cells in the pineal gland from tryptophan, an essential amino acid. Tryptophan is biosynthesized to serotonin, after which enzymes within the pineal gland transform serotonin into melatonin [10], which is then released into circulation to reach central and peripheral target tissues.

Melatonin exerts its action on circadian rhythms such as the sleep-wake rhythm, neuroendocrine rhythms, or body temperature cycle due to its effects on MT1 and MT2 receptors [11-13].

It is also a powerful antioxidant and free radical scavenger that is twice as active as vitamin E [14]. Through complex signaling processes via its receptors, melatonin promotes the expression of antioxidant enzymes such as superoxide dismutase, glutathione peroxidase, and catalase among others [13,15].

In response to darkness, the pineal gland commences melatonin production, whereas light exposure causes this process to slow or cease. Exposure to room light before bed suppresses the onset of melatonin and shortens its duration [16]. This is all regulated by the suprachiasmatic nucleus in your hypothalamus. If you’re a practitioner, you can learn more about this in the chronobiology module in the Essential Certification of Health Optimization Medicine and Practice at homehope.org.

Melatonin is also directly produced in the mitochondria, the energy factories of the cell, and influences glucose metabolism. In fact, the pineal gland only produces around 5% of the total melatonin in the body [17].

Melatonin Supplementation

Melatonin is available in certain jurisdictions as a dietary supplement and lots of people use it to help with their sleep, but is there a fundamental need for this?

In most studies, melatonin decreases sleep onset latency, increases total sleep time, and improves the quality of that sleep. In simple terms, it speeds up the process of getting to sleep and helps with staying asleep [18].

As we age, melatonin production decreases, which can cause the antioxidant capacity of the skin to decrease, for example, as well as dysregulate the clock genes that regulate circadian rhythm [19]. Therefore, melatonin supplementation in older adults might have a rational basis.

There are several different types of melatonin supplements available, comprising natural (obtained from the pineal gland of mammals) and synthetic (i.e., man-made) varieties [20].

A recent meta-analysis of available research studies conducted by scientists in Iran found that supplementing with exogenous melatonin had positive effects on sleep quality based on the Pittsburgh Sleep Index assessment tool [21]. These beneficial effects were found in adults with respiratory diseases, metabolic disorders, and primary sleep disorders but not mental disorders, neurodegenerative conditions, or other diseases.

Is Melatonin Supplementation Safe?

In general, animal and human studies seem to show that melatonin supplementation is safe over the short-term, even in extreme doses. High doses have been used for a variety of conditions, most recently COVID-19 prevention and treatment, whereas low doses are used to treat jet lag and sleep problems [22].

Only mild adverse effects such as dizziness, headaches, nausea, and sleepiness have been reported. Moreover, long-term randomized clinical studies have indicated that melatonin should only induce mild adverse effects compared to a placebo [23-25]. However, due to a lack of human studies, pregnant and breastfeeding women are advised not to use exogenous melatonin until further investigations have been carried out. Additionally, in pediatric special populations, melatonin should be used at both the patient’s and physician’s discretion [26].

There have been some reports of melatonin supplementation lowering testosterone levels but there isn’t really any evidence of this. In fact, a cross-sectional study from last year showed that low-dose melatonin (approximately 1 mg per day for more than 30 days) had no association with testosterone levels in males over the age of 18 in the United States [27]. These findings are consistent with an older double-blind, placebo-controlled study that found no impact of oral melatonin (at a larger dose of 6 mg per day for one month) on the secretion of reproductive hormones, including testosterone, in healthy adult men [28].

A key area of concern with melatonin supplementation is the fact that the declared concentration of melatonin in a given product might not be congruent with that on the label [29,30]. A very recent study in the Journal of the American Medical Association showed that only 12 out of 30 reviewed preparations contained quantities that were within 10% of those advertised, with some containing up to 347% of the declared amount [31]. This is why it is absolutely essential to buy melatonin (and all your supplements) from manufacturers that adhere to strict standards such as GMP, third party testing, their own purity/potency testing, and will share all this information with you if you request it. 

Summary

In this article we have provided some background on melatonin, what it is, how it works, and how supplementation can be used to improve sleep quality, especially as we age. We have also discussed the (very few)  contraindications and risks associated with melatonin supplementation plus the lack of any convincing data that testosterone levels will drop using it.  

Consider melatonin as a sleep aid, especially for sleep induction and possibly maintenance as well.  And of course, there is always Tro Calm to quiet your mind, turn off those intrusive thoughts, and help you fall asleep. 

References

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