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Long-term use of melatonin supplements has been associated with a higher risk of developing heart failure among adults with chronic insomnia, according to a new study.
The findings do not prove that melatonin itself causes heart failure, but researchers said they raise questions about the long-term safety of a supplement widely considered a natural and harmless sleep aid.
Researchers used five years of de-identified medical records from the TriNetX Global Research Network, focusing on adults diagnosed with chronic insomnia. Participants with at least 12 months of documented melatonin use were compared with similar insomnia patients who had no record of using the supplement.
People who already had heart failure or had been prescribed other sleep medications were excluded.
The analysis found that 4.6 per cent of long-term melatonin users developed heart failure over the following five years, compared with 2.7 per cent of non-users. This represented about a 90 per cent higher risk among those with documented long-term melatonin use.
“Melatonin supplements may not be as harmless as commonly assumed,” said lead author Dr Ekenedilichukwu Nnadi, chief resident in internal medicine at SUNY Downstate/Kings County Primary Care in Brooklyn, New York.
The researchers stressed that the study found an association rather than a cause-and-effect relationship. Further research will be needed to determine whether melatonin contributes directly to heart failure risk or whether other factors explain the association.
Melatonin is a hormone naturally produced by the brain’s pineal gland that helps regulate the sleep-wake cycle. Synthetic melatonin is commonly used for insomnia and jet lag and is available over the counter in many countries.
The researchers said evidence on the cardiovascular safety of prolonged melatonin use remains limited and called for further studies to assess its long-term effects.