Study Reveals a Concerning Link Between Melatonin and Heart Failure
A groundbreaking study unveiled at the American Heart Association's (AHA) annual conference in New Orleans has raised serious concerns about the long-term use of melatonin supplements. The research, which has not yet undergone peer review, found that prolonged melatonin use is linked to a 90% increase in heart failure risk, a 3.5-fold higher risk of heart failure hospitalization, and nearly double the risk of death from any cause among chronic insomnia sufferers who took melatonin for a year or more.
Understanding Melatonin
Melatonin is a natural hormone produced by the pineal gland in the brain
that helps synchronize the body's internal clock. Its levels naturally
rise with darkness and fall with daylight. A synthetic version of this
hormone is manufactured and marketed as a dietary supplement, available
without prescription in many countries, including the United States.
These supplements are promoted as a natural means to improve sleep
quality, but unlike prescription medications, they are not subject to
stringent oversight. As a result, dosage strength, purity, and
composition can vary significantly between manufacturers.
Dr. Jennifer Zeitzer, a neurologist and
sleep medicine specialist, explains that most people take melatonin
without consulting a physician. "In observational studies where the
control group is defined by prescription records, it's difficult to know
in practice who among the participants actually took the supplement and
who didn't," she notes.
She points to another study that examined dozens of melatonin gummy
brands and found extreme variation in composition: some products
contained no melatonin at all, while others contained amounts four times
higher than stated on the packaging. "In the United States, melatonin
is considered a supplement and therefore is not subject to strict
oversight." she emphasizes.
What Did the Study Examine?
The data was drawn from the massive TriNetX Global Research Network,
which contains real, de-identified electronic medical records from
various countries. Researchers analyzed five years of data from 130,828
adults diagnosed with chronic insomnia, with an average age of 55.7
years, of whom 61.4% were women.
Of all participants, 65,414 received at least one melatonin prescription
and were reported as having taken it for at least a year, while a
control group with similar characteristics included people with insomnia
who had no mention of melatonin use in their records.
The two groups were matched according to no
fewer than 40 parameters: age, gender, ethnicity, heart diseases and
nervous system conditions, cardiac and neurological medications, blood
pressure, body mass index (BMI), and more. The analysis excluded people
who had previously been diagnosed with heart failure or who had used
other sleep medications such as benzodiazepines.
Alarming Findings: More Hospitalizations, More Deaths
According to the AHA's statistics for 2025,
approximately 6.7 million adults in the U.S. live with heart failure - a
condition in which the heart cannot pump enough oxygen-rich blood to
the organs, preventing them from functioning properly.
The primary analysis found that among adults with insomnia, those who
took melatonin for a year or more had approximately 90% higher risk of
developing heart failure during the five-year follow-up period compared
to non-users (4.6% versus 2.7%). Even when researchers tightened the
definition of "prolonged use" and required at least two prescriptions 90
days apart, similar findings emerged - an 82% increase in heart failure
risk among users.
In secondary analysis, melatonin users were
found to be nearly 3.5 times more likely to be hospitalized for heart
failure (19% versus 6.6%), and almost twice as likely to die from any
cause during the five-year follow-up period (7.8% versus 4.3%).
Expert Perspectives and Cautions
Dr. Akandy Nandi, the study's lead author, stated in the AHA press
release: "Melatonin supplements may not be as benign as commonly
believed. If our study is confirmed, it could impact how physicians
advise patients about sleep supplements." He added that "melatonin is
considered a natural and safe supplement that aids better sleep, so it
was surprising to discover such a consistent and significant increase in
serious health outcomes - even after accounting for many other risk
factors."
Study Limitations
However, the researchers emphasize that the findings do not prove that
melatonin causes heart failure. The primary reason is that the database
included countries where melatonin is sold by prescription only
alongside countries where it's freely available, but patient locations
were not included in the data. Therefore, melatonin use was defined only
by prescription records, and participants who took it as a supplement
without prescription were mistakenly classified as non-users - a
limitation that weakens the ability to establish a direct causal
relationship.
The researchers clarified in the AHA
statement that this could distort the analysis, since some "non-users"
actually did take melatonin.
Additionally, researchers lacked data on the severity of participants'
insomnia or the presence of accompanying psychiatric disorders such as
depression or anxiety, which could affect both the need for sleep
supplements and cardiac risk.
"It's possible that some patients in the study used melatonin to treat
sleep problems that don't stem from a disorder in hormone production,
and therefore the supplement wasn't the appropriate treatment for them,"
explains Dr. Zeitzer. "It's possible that the sleep problems themselves
- not the melatonin - ultimately led to increased risk for heart
problems."
Dr. Nandi noted in the AHA statement that
severe insomnia, depression, anxiety, or use of other sleep medications
could be confounding factors associated with both melatonin use and
increased cardiac risk. He stated that while the findings raise
important questions about the safety of one of the world's most common
sleep supplements, they do not prove a direct causal relationship. He
emphasized the need for additional research to examine melatonin's
effects on heart health.
The Bottom Line
This preliminary study serves as a important cautionary tale about the
assumption that "natural" supplements are inherently safe. While the
research doesn't definitively prove that melatonin causes heart
problems, it raises significant red flags that warrant further
investigation and suggest that people - especially those with existing
heart conditions or risk factors - should consult with healthcare
providers before starting long-term melatonin supplementation.