Melatonin: Hormones and Metabolism

Melatonin interacts with various hormones in the body, including cortisol, the stress hormone, and reproductive hormones such as estrogen and testosterone. Prolonged or excessive use of melatonin supplements can disrupt the delicate balance of these hormones, leading to potential side effects and imbalances.

For instance, studies show that melatonin may act as an inhibitor to (meaning interferes with), the human chorionic gonadotropin (hCG) pathway. This can have effects on androgen production (hormones like DHEA and testosterone). It can also interact with the local corticotropin-releasing hormone (CRH) system. The CRH system is involved in how we respond to stress and how our bodies use energy.

These hormone interactions should raise some flags of potential concern for the long-term use of melatonin - especially in people trying to maintain their fertility and in children. 

Melatonin can also impact metabolism, specifically through glucose regulation - or how we use and produce energy from sugar. 

Studies have suggested that melatonin supplementation may affect insulin sensitivity, glucose tolerance, and overall metabolic function.

For example, a study published in the journal Cell Metabolism, which used both mouse and human models, found that higher levels of melatonin can negatively affect the ability of beta cells to produce insulin. 

Beta cells are important for controlling blood sugar levels. The researchers also discovered that this effect is more prominent in individuals who have a specific gene variant in the melatonin receptor gene MTNR1B, which is associated with a higher risk of Type 2 diabetes. 

Interestingly, the study revealed that inhibiting insulin may have a protective effect against nocturnal hypoglycemia, or low blood sugar levels at night, when melatonin levels are high but energy demands are low.

Another study, published in the journal Clinical Endocrinology, focused on postmenopausal women. The researchers administered either 1 mg of melatonin or a placebo to the participants in the morning. After 45 minutes, they conducted glucose tolerance testing. The study found that those who received melatonin had reduced glucose tolerance and lower sensitivity to insulin. 

This means their bodies had more difficulty processing and controlling blood sugar levels compared to those who took the placebo.

In a separate study published in the journal Sleep, researchers investigated the effects of supplemental melatonin on glucose tolerance in healthy women. They primarily focused on two important measures: the incremental area under the curve (AUC), which describes the total rise in glucose over time and is used to diagnose impaired glucose tolerance, and the maximum concentration (Cmax) of plasma glucose. 

The study revealed that melatonin supplementation in the evening decreased insulin sensitivity, resulting in a 54% increase in glucose AUC and a 27% increase in glucose Cmax. 

In the morning, melatonin impaired glucose tolerance by reducing insulin release, leading to a remarkable 186% increase in glucose AUC and a 21% increase in glucose Cmax.

These studies highlight that melatonin can influence our body's metabolism and ability to regulate blood sugar levels - and that the effects can spillover into the next day. 

However, it's important to remember that these effects can vary depending on the time of day and individual factors. The research provides valuable insights into the complex relationship between melatonin and metabolic health.

Regular use of melatonin supplements can lead to a decrease in the effectiveness of the hormone over time.

Some studies have shown that the long-term positive effects of taking melatonin for sleep appear to be limited, finding that after 12 months, the sleep of participants isn't measurably different from people taking a placebo.

This means that higher doses may be required to achieve the same sleep-inducing effects, leading to a potential cycle of dependence. Additionally, abruptly discontinuing melatonin after prolonged use may result in rebound insomnia or sleep disturbances.

It's clear that, while melatonin most often gets associated with the idea of “sleep”, it has many other roles to play. It is one of nature's most versatile biological signals.

There are many studies pointing to the benefits of melatonin. Which also has to do with the fact that it plays to many roles. 

We certainly do not want too little of it. With increased levels of stress and increased light exposure, especially at night time, there is also a case to be made that many people might have low levels of melatonin. 

As with all hormones, there is a ‘Golidlocks’ zone. We do not want to have too much or too little of this hormone. The best case being that we have good consistent bed time habits, manage the light in our environment, and support our body with the right nutrients to make the right amount of melatonin (at the right time) on its own.