A new study recently published in the journal Microorganisms shows that melatonin, despite its antioxidant properties and role in sleep cycle regulation, could intensify intestinal inflammation and impair the action of gut microbiota. This assembly of bacteria and other microbes plays a crucial role in maintaining health by aiding in digestion and enhancing the immune system. An upset balance between unhealthy and healthy microbes in the intestines could potentially contribute to issues like weight gain, elevated blood sugar levels, abnormal cholesterol levels, and other health disorders.

Often referred to as the “sleep hormone”, melatonin is widely used as a dietary supplement (typically without a physician’s approval) by individuals suffering from sleep problems.

“It’s generally thought to be harmless. After all, it’s a hormone and can help regulate sleep. However, our study shows that people should be careful about taking hormone supplements and that the ingestion of melatonin supplements can have adverse effects on health,” said Cristina Ribeiro de Barros Cardoso, a professor of immunology and neuroimmunoendocrinology at the University of São Paulo’s Ribeirão Preto School of Pharmaceutical Sciences (FCFRP-USP) in São Paulo state, Brazil.

Cardoso’s laboratory conducts research into inflammatory bowel disorders, including Crohn’s disease and ulcerative colitis. These disorders are immune-mediated, resulting from abnormal activity of the immune cells in overreacting to a pathogen, with destructive effects on the gut microbiome and severe clinical symptoms, such as abdominal pain, constant diarrhea, bleeding, and fatigue.