New Research Links Long-term Melatonin Use to Heart Risks

New research into a widely used sleep aid is raising concerns among some scientists about its long-term use.

An as-yet unpublished, non-peer-reviewed analysis of adults with insomnia suggests that people prescribed melatonin for longer than a year may face a higher risk of heart problems.

Long-term melatonin use and heart failure risk

The study examined more than 130,000 adults in several countries. Over five years, participants prescribed melatonin on a long-term basis had an 89 percent greater risk of heart failure and were twice as likely to die from any cause as people who had not been prescribed melatonin.

A separate analysis indicated that people taking melatonin for more than a year were almost 3.5 times more likely to be admitted to hospital with heart failure than those not taking it. The risk of death from any cause also rose from 4.3 percent to 7.8 percent between the groups.

These early results do not alter current health guidance, nor do they prove that melatonin – the fourth most popular natural product used by adults in the US – is responsible for harmful effects.

However, the findings indicate that longer-term melatonin use requires further investigation to establish whether it is safe.

The research was presented in November at the American Heart Association's Scientific Sessions.

"Melatonin supplements may not be as harmless as commonly assumed," says medical researcher Ekenedilichukwu Nnadi at SUNY Downstate/Kings County Primary Care in New York. "If our study is confirmed, this could affect how doctors counsel patients about sleep aids."

How melatonin is used

Melatonin supplements mimic a hormone produced naturally by the brain that helps regulate the body's internal clock. Taking this replacement hormone late in the day may help some people both get to sleep and remain asleep.

For people who are neither pregnant nor breastfeeding, melatonin is generally regarded as safe and well tolerated when used in the short term – roughly 1 to 2 months.

Evidence on the supplement's effects beyond that period is limited. Some researchers argue that this gap needs addressing, particularly as melatonin becomes increasingly popular.

In the US and numerous other countries, melatonin supplements can be bought over the counter. As a result, people may use them without clinical advice or supervision regarding dose or duration of use.

Although some research has suggested that long-term melatonin use is safe, comprehensive studies remain unavailable.

Important limitations of the study

The analysis by Nnadi and colleagues drew on electronic health records from adults in the US as well as the UK, where melatonin is available only on prescription.

While the findings are concerning, they should be interpreted carefully because the study has an important methodological limitation.

Researchers did not ask participants directly about their melatonin use. Instead, they relied on prescription records to identify who was taking the supplement. This means the comparison group of people not taking melatonin could have included US residents who were using over-the-counter melatonin without a prescription.

Carlos Egea, President of the Spanish Federation of Sleep Medicine Societies, who was not involved in the study, highlighted this limitation in an expert response to the research. Nevertheless, he considers the associations reported by the study significant.

"These findings challenge the perception of melatonin as a benign chronic therapy and only highlight the need for a prospective trial with a control group to clarify its safety profile," argues Egea.

Even over the short term, melatonin may have drawbacks that many users do not know about. For example, a recent cluster of non-fatal overdoses among children in Australia has prompted questions about the supplement's safety profile for particular age groups.

Melatonin products may be derived from a natural hormone, but that does not mean they are without risks.

The recent findings were presented in November at the American Heart Association's Scientific Sessions.