Folks using melatonin supplements as a sleep aid might be putting themselves at risk for future heart problems, a new study says.

Adults with insomnia who’d been using melatonin for a year or more had 90% higher odds of heart failure, researchers are scheduled to report Nov. 10 in New Orleans at a meeting of the American Heart Association.

Further, people taking melatonin are nearly 3.5 times more likely to be hospitalized for heart failure, researchers found.

“Melatonin supplements are widely thought of as a safe and ‘natural’ option to support better sleep, so it was striking to see such consistent and significant increases in serious health outcomes, even after balancing for many other risk factors,” lead researcher Dr. Ekenedilichukwu Nnadi said in a news release. He’s chief resident in internal medicine at SUNY Downstate/Kings County Primary Care in Brooklyn, New York.

Melatonin is a hormone that naturally occurs in the body and helps regulate people’s sleep-wake cycle. Levels increase during darkness and decrease during daylight.

Doctor: Hidden Stroke Triggers Could Be Lurking in Your Daily Routine, Click Here.

Melatonin supplements are widely available over the counter in the United States, and are promoted and marketed as a safe sleep aid, researchers noted.

To see how long-term melatonin use might affect people’s health, researchers reviewed five years of electronic health records for nearly 131,000 people diagnosed with chronic insomnia. More than 65,000 reported taking melatonin for more than a year.

The team compared people who’d used melatonin long-term to people who’d never had melatonin use noted in their health records.

Over five years, heart failure occurred in about 4.6% of melatonin users versus 2.7% of non-users, a 90% difference.

Heart failure also was 82% higher when researchers looked at people who had at least two melatonin prescriptions filled at least 90 days apart, based on records from the U.K.

Those taking melatonin were about 3.5 times more likely to be hospitalized for heart failure (19% versus 6.6%) and twice as likely to die during the study period (7.8% versus 4.3%), results showed.

”I’m surprised that physicians would prescribe melatonin for insomnia and have patients use it for more than 365 days, since melatonin, at least in the U.S., is not indicated for the treatment of insomnia,” AHA spokeswoman Marie-Pierre St-Onge said in a news release. She’s director of the Center of Excellence for Sleep & Circadian Research at Columbia University Irving Medical Center in New York City.

“In the U.S., melatonin can be taken as an over-the-counter supplement and people should be aware that it should not be taken chronically without a proper indication,” added St-Onge, who was not involved in the study.

However, more research is needed to fully understand the relationship between melatonin supplements and heart health, Nnadi said.

“Worse insomnia, depression/anxiety or the use of other sleep-enhancing medicines might be linked to both melatonin use and heart risk,” he said. “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.”

Findings presented at medical meetings should be considered preliminary until published in a peer-reviewed journal.