Melatonin is a hormone produced naturally by the pineal gland, a small structure in the brain, primarily recognized for regulating the sleep-wake cycle. Its secretion increases in the evening, signaling the body to prepare for sleep and synchronizing internal processes with the 24-hour day-night cycle. Melatonin supplementation is commonly used as an over-the-counter sleep aid. The question of whether this supplementation might cause weight gain is a widespread concern, given the hormone’s broad influence on biological systems. This review explores the current scientific understanding of melatonin’s direct clinical impact on body weight and its complex interactions with metabolic pathways.
Melatonin’s Role in Circadian Rhythms
The primary role of melatonin is to act as the body’s chemical signal of darkness. Produced almost exclusively at night, this hormone governs the circadian rhythm, the internal clock coordinating essential biological activities over a 24-hour period. By signaling the shift from day to night, melatonin helps regulate the timing of physiological functions, including body temperature, blood pressure, and hormone release.
Disruption of these rhythms can affect various bodily systems. Melatonin is widely available as a dietary supplement, primarily used to manage sleep disturbances like insomnia or jet lag. Supplemental use introduces a higher concentration of the hormone, leading to questions about effects beyond sleep regulation.
Investigating the Direct Link to Weight Gain
Clinical studies investigating the direct impact of melatonin supplementation on body weight metrics, such as Body Mass Index (BMI) or total weight, generally do not support the idea that it causes weight gain. Research focusing on standard melatonin doses shows no significant correlation with weight increase over time. The fear that melatonin might lead to weight gain appears unfounded in human data.
Reviews of human trials suggest that melatonin supplementation, particularly at doses of 8 milligrams per day or less, may be associated with beneficial changes. These include stabilization or minor reductions in body weight, BMI, or waist circumference, especially in populations with metabolic challenges. While large-scale studies are needed to confirm a strong weight-loss effect, the scientific consensus indicates that melatonin supplementation is unlikely to cause weight gain.
Melatonin’s Influence on Metabolism and Fat Regulation
Melatonin’s metabolic effects are far-reaching because receptors are found on cells throughout the body, including those within adipose (fat) tissue. Melatonin acts as an endocrine regulator, influencing how the body handles and stores energy, a role separate from its function as a sleep signal. This activity generates interest in its potential anti-obesity properties.
A primary mechanism involves the modulation of brown adipose tissue (BAT), a type of fat specialized in burning calories to generate heat (thermogenesis). Melatonin increases the activity and volume of BAT, encouraging the body to expend energy rather than store it. It also promotes the “browning” of white adipose tissue, transforming energy-storing fat cells into more metabolically active, brown-like cells.
The hormone also improves how the body manages sugar by enhancing insulin sensitivity. Better insulin function allows cells to utilize glucose more effectively, which helps prevent metabolic dysfunction that often precedes weight gain. Melatonin can also positively influence lipid metabolism, potentially leading to improved blood profiles, such as reduced levels of triglycerides and cholesterol.
Addressing Sleep Quality, Appetite, and Weight
The most recognized link between melatonin use and healthy weight management is indirect, mediated through the restoration of quality sleep. Chronic sleep deprivation is a risk factor for weight gain because it disrupts the balance of key appetite-regulating hormones. Poor sleep elevates the hunger-stimulating hormone ghrelin while suppressing the satiety hormone leptin.
This hormonal imbalance leads to increased hunger, a preference for high-calorie foods, and greater total caloric intake. Sleep loss also triggers an increase in the stress hormone cortisol, which favors fat storage, particularly in the abdominal area, and impairs glucose metabolism.
By promoting better sleep quality, melatonin supplementation helps normalize these disrupted hormonal and metabolic pathways. When individuals achieve adequate, restorative sleep, the balance between ghrelin and leptin is restored, cortisol levels are regulated, and insulin sensitivity improves. Any beneficial effect of melatonin on body weight often results from correcting the metabolic consequences of previously poor sleep.