Weight Loss

There is several evidences that melatonin is significantly involved in energy metabolism and body weight regulation. Melatonin is a versatile substance found in unicellular organisms, fungi, plants and animals that is more primitively related to protection against oxidative stress but which along the evolutionary line has acquired several other biological functions, notably the transduction of environmental information, particularly the photoperiod, temperature and food availability.

Endogenous melatonin has been demonstrated to be the mediator of seasonal changes in body weight in some small mammals, an effect that probably involves the modulation of brown adipose tissue activity. Brown adipose tissue, an organ exclusively found in mammals, acts to keep the balance between energy intake and energy expenditure by means of disposing the extra energy as heat. Interestingly, it has been recently demonstrated that, contrary to what was presumed earlier, substantial amounts of metabolically active brown adipose tissue are present in human adults. Based on this finding, it has been speculated that melatonin-induced hypertrophy and functional activation of brown adipose tissue may also apply to humans, thus providing a potential target for the treatment of obesity.

Exogenous melatonin administration in animals has been shown to cause significant weight loss and lower food intake, intra-abdominal fat and appetite. In contrast, to our knowledge, no clinical trials have evaluated the weight lowering potential of melatonin in humans, although it is recognized that melatonin administration is safe and well tolerated. However, data from the VITamins And Lifestyle cohort study of western Washington, in which participants (n=15,655) completed questionnaires about 10-year supplement use, diet, health habits, height, and present and former weight, showed that after adjusting for confounding factors, melatonin supplementation was related to weight loss and less weight regain.

Patients with obesity commonly suffer from multiple comorbidities, including sleep disorders, which can  sometimes benefit from melatonin administration, and an increasing number of studies using this substance have been carried out in recent years, also including obese subjects. We suggest that changes in body weight, appetite and food intake should be included in current and future clinical trials of melatonin as a simple, inexpensive and practical means of gathering evidence for the potential benefits of this substance in obesity. Also, eligibility and deferral criteria for melatonin administration in people with sleeping disorders should be revisited based on their body weight. Large clinical trials on the efficacy of melatonin as an adjunct in weight loss therapies and other clinical outcomes in obese people are also warranted.