A study presented at the American Heart Association's scientific meetings has raised concerns about melatonin, one of Britain's most commonly prescribed sleep aids. The findings suggest that long-term users face a higher risk of heart failure. But the preliminary data demands careful scrutiny before the alarm is sounded.
Author
- Heba Ghazal
Senior Lecturer, Pharmacy, Kingston University
Melatonin has been prescribed in the UK for nearly two decades, with 2.5 million prescriptions issued in England last year alone . The drug is a synthetic version of the hormone naturally produced in the brain - the so-called "hormone of darkness" that regulates our sleep-wake cycle.
For years, it's been considered safe for treating short-term sleep problems in adults and, under specialist supervision, for children with learning disabilities or ADHD.
The study, published only as a brief summary , analysed electronic health records of roughly 130,000 adults with sleep difficulties over five years - half of whom took melatonin and half of whom didn't.
People who took melatonin for at least a year were roughly three times more likely to be hospitalised with heart failure than non-users (19% of people who took melatonin versus 6.6% of people who did not). Long-term users also faced higher rates of heart failure diagnosis and death from any cause.
The researchers attempted to balance their comparison by matching melatonin users with non-users across 40 factors, including age, health conditions and medications. Yet the study found only an association, not causation. This distinction matters. Correlation doesn't prove that melatonin caused heart failure.
The devil, as ever, lives in the missing details. Only a 300-word summary of the study exists so far, meaning crucial information - melatonin dosage, insomnia severity, lifestyle factors - remains unreported.
The study's methodology raises questions. It relied on electronic medical records rather than direct patient follow-up or interviews, which can leave gaps in the data. The research drew from TriNetX Global Research Network, a large international database. But healthcare practices and record-keeping vary wildly between hospitals and nations, potentially skewing results.
In the UK, melatonin requires a prescription for specific conditions. But in the US, it's sold over the counter - purchases that are often not documented in medical records. This means some people categorised as non-users may actually have been taking melatonin, muddying the comparison.
The missing piece of the puzzle
Even assuming both groups were correctly identified and matched, a key question lingers: why did one group receive melatonin while the other didn't? Perhaps those prescribed the drug suffered more severe or disruptive sleep problems - symptoms that might reflect underlying health issues, including heart problems. If so, melatonin might simply be a marker of existing risk rather than the cause of it.
Intriguingly, previous studies in heart failure patients suggested melatonin may actually protect heart health by improving psychological wellbeing and heart function. Other research indicated it could ease symptoms in people with heart failure and serve as a safe complementary therapy.
Since the study exists only as an abstract, it hasn't undergone peer review. And information on the study's methods and results remains limited. While the findings are noteworthy and raise legitimate questions about the long-term risks of using this supplement, they're far from conclusive. Further studies are needed to determine whether prolonged melatonin use affects heart health, and if so, how.
Doctors face a familiar balancing act: weighing treatment benefits against potential risks. Poor sleep doesn't just affect the heart; it's linked to problems with metabolism, mental health and the immune system, among others.
Doctors typically start with lifestyle changes, better sleep habits and talk therapy. But when these fail to improve sleep quality, short-term medication may be necessary to restore healthy patterns and prevent further health complications.
The melatonin story isn't over. It's just beginning. Until fuller evidence emerges, panic seems premature.
Heba Ghazal does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
