The Summary
In a randomized, double-blind, crossover trial, researchers investigated how melatonin affects glucose metabolism. Twenty-one healthy participants—ten carrying the MTNR1B diabetes risk gene variant and eleven noncarriers—underwent a controlled five-day laboratory protocol. Participants received either 5 mg of oral melatonin or a placebo before undergoing intravenous glucose tolerance tests. The results showed that melatonin significantly worsened glucose tolerance and slashed early insulin secretion by 40% only in those carrying the risk gene variant. It also disrupted insulin feedback loops, demonstrating a clear gene-supplement interaction that impairs blood sugar regulation.
Why this is interesting
Melatonin use has skyrocketed, but we are only beginning to understand its metabolic side effects. This study challenges the assumption that melatonin is universally safe, showing it can actively impair insulin production in people with a common genetic predisposition. For the millions of people who take melatonin nightly, this means a seemingly harmless sleep aid could be quietly contributing to insulin resistance and type 2 diabetes risk. It underscores the critical need for personalized, genotype-based medical advice before starting daily hormone supplementation.