Can melatonin lower testosterone levels?
No, taking exogenous melatonin through melatonin supplements is unlikely to lower your testosterone level. However, science shows that the organs that produce testosterone can be influenced by your body's natural melatonin.
What is Melatonin?
Melatonin is a hormone naturally produced in the pineal gland at nightfall [2]. Dimming light stimulates the release of melatonin, registered by melanopsin cells at the back of the eye. These cells consequently signal to the pineal gland that it should start making and releasing melatonin.
Melatonin has a spectrum of actions in the body. Increased melatonin levels are primarily linked to winding down for the night, increasing sleepiness and promoting relaxation, which works in concert to improve sleep quality. However, melatonin can regulate reproductive processes, protect cells and neurons against oxidative stress and control glucose metabolism [3].
Melatonin Supplements
Exogenous melatonin in the form of melatonin supplements is primarily used to manage jet lag and insomnia [4, 5]. These supplements contain an artificial form of melatonin, which can promote sleepiness but not sleep itself. This function of melatonin is distinct to benzodiazepines or barbiturates, which suppress the activity of the brain, sending you into a sleep-like state. Indeed, taking melatonin to promote sleepiness resulted in better outcomes in patients with impaired sleep compared to Xanax and other benzodiazepines [6].
Melatonin has also been used to delay the deterioration of symptoms in frontotemporal dementia and Alzheimer’s disease and other neurodegenerative conditions, protect cells in chemotherapy for cancer. Melatonin could also prevent cancer progression or even manage symptoms of depression and seasonal affective disorder [7].
Can Melatonin Lower Testosterone?
The Significance Of Testosterone
Melatonin acts on multiple organs throughout the body, influencing many other hormones. The steroid hormone testosterone is the primary male sex hormone linked to the development of male sexual characteristics, libido, hair growth, and voice lowering. It is also linked to muscle growth, which has made it popular in sports where additional muscle provides an advantage, such as bodybuilding or boxing [8].
Testosterone can also be found in women in small quantities. Higher levels of testosterone in women may indicate an underlying health condition, such as polycystic ovary syndrome or cervical cancer. In both men and women, excess testosterone can be a sign of Cushing’s syndrome, tumours in the sex organs or adrenal gland [8]. It is, therefore, critical to maintain a healthy testosterone balance for your sex and age.
Melatonin and Testosterone
The existing literature has generated mixed evidence about the effect of melatonin on testosterone. The testicles express two different melatonin receptors, indicating that melatonin can influence testosterone production, male reproduction, and sexual health [9]. Female ovaries also express a subtype of the melatonin receptor, which could regulate fertility in specific seasons [7].
The first line of evidence that melatonin is bad for testosterone levels is that since melatonin supplements have become popular, testosterone levels in males have declined [10]. However, this does not mean that there is a direct link between supplementing melatonin and reduced testosterone.
A large cross-sectional study consequently investigated the direct effects of melatonin supplementation in healthy US males over 18 years old. In contradiction to the claim above, the researchers found no effect of melatonin on testosterone [10].
An earlier study looked at the overall effects of melatonin on male reproductive hormones, which, amongst testosterone, also include gonadotropin-releasing hormone and luteinizing hormone. This study looked at the molecular mechanisms through which melatonin could regulate testosterone. They found that melatonin was important for releasing testosterone from Leydig cells, specialized cells in the testes, but did not directly state whether melatonin increased or decreased testosterone levels.
Melatonin Can Protect Testosterone-Producing Organs
Another role of melatonin is that it is anti-carcinogenic and protects cells. Through this property, melatonin can help tackle chemotherapy-induced damage to the testicles, which has been demonstrated in animal models [11]. In these animal studies, melatonin administration reduced damage to the testicles, yet whether this is also true in humans remains to be established in further clinical trials. Nonetheless, the animal literature indicates that melatonin could have testosterone-sparing benefits, particularly in patients with cancer.
Summary: Melatonin’s Effect On Testosterone
To summarize, melatonin does affect the molecular mechanisms of testosterone production and release. This is likely due to its role in regulating seasonal behaviours and the evolutionary benefits of seasonal fertility. Nonetheless, there is not sufficient evidence to support melatonin reducing or increasing testosterone levels when taken as a supplement. If you are taking melatonin and are worried about your testosterone profile, a regular blood exam prescribed by your healthcare professional can provide further insight into your testosterone levels.