Adults who use melatonin for chronic insomnia are more likely to be diagnosed with heart failure, require hospitalisation or die from any cause compared with those who don’t use the supplement, preliminary findings suggest.

Presented at the American Heart Association Scientific Sessions in New Orleans, US researchers said their findings challenged the perception of the widely available supplement being a benign chronic therapy and underscored the need for randomised trials to clarify melatonin’s cardiovascular safety profile.

Using an international database, the researchers reviewed data from 130,828 adults with an insomnia diagnosis (mean age 56, 61% women), of which half had used melatonin for at least a year and half had no recorded melatonin use.

The groups were matched for demographic factors, comorbidities, medications, laboratory results, vital signs, and healthcare utilisation, and excluded if they had been prescribed other sleeping pills or had heart failure previously.

Findings showed long-term melatonin users had about 90% higher chance of incident heart failure over five years versus non-users (4.6% vs 2.7%, respectively; HR 1.89).

When confining the analysis to people who had at least two melatonin prescriptions filled at least 90 days apart, they had a 82% higher chance.

A secondary analysis showed that people taking melatonin were nearly 3.5 times as likely to be hospitalised for heart failure when compared to those not taking melatonin (19.0% vs 6.6%, respectively, HR 3.44) over the five-year period.

Participants in the melatonin group were also twice as likely to die from any cause than those in the non-melatonin group (7.8% vs 4.3%, respectively, HR 2.09).

“Melatonin supplements may not be as harmless as commonly assumed. If our study is confirmed, this could affect how doctors counsel patients about sleep aids,” said lead author Dr Ekenedilichukwu Nnadi, a chief resident in internal medicine at SUNY Downstate/Kings County Primary Care, New York.

But he said other factors might have also been at play that weren’t accounted for in the study, such as severity of insomnia, and presence of psychiatric disorders such as depression and anxiety, which might be linked to melatonin use and cardiovascular risk.

“Also, while the association we found raises safety concerns about the widely used supplement, our study cannot prove a direct cause-and-effect relationship. This means more research is needed to test melatonin’s safety for the heart,” he said.