Long-term melatonin use may increase the risk of heart failure, study finds

An over-the-counter sleep aid may put some users at higher risk for heart failure and death.

In a preliminary study of adults with insomnia, researchers found as association between long-term melatonin use and heart failure. People who took the supplement for at least one year also were more likely to die than those who did not use melatonin.

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The findings, which have not yet been published in a peer-reviewed journal, could alter current approaches to sleep medicine, researchers said.

"Melatonin supplements may not be as harmless as commonly assumed," Dr. Ekenedilichukwu Nnadi, lead author of the study, said in a statement. "If our study is confirmed, this could affect how doctors counsel patients about sleep aids."

The study drew on the medical records of 130,828 adults diagnosed with insomnia. They were divided into two groups: those with a documented use of melatonin of at least one year and those without any mention of the sleep aid in their records. The researchers reviewed each patient's records over five years and found those taking melatonin had an 89% higher chance of heart failure than those in the non-melatonin group.

The melatonin users also were nearly 3 1/2 times more likely to be hospitalized for heart failure, and almost twice as likely to die from any cause than their peers.

Researchers noted several limitations in the study. They did not have access to information like the severity of the subjects' insomnia or their histories with other psychiatric disorders. Most significantly, they drew records from countries like the U.S., where melatonin does not require a prescription, and the United Kingdom, where it does. This complicates the categorization of the groups, because over-the-counter melatonin use would not necessarily be documented.

The preliminary findings will be presented at the American Heart Association's Scientific Sessions conference on Monday, Nov. 10.

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

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