Melatonin, the 'natural' bedtime pill. But is it really safe?

And the resulting results, given the sheer magnitude of the numbers examined, are difficult to dismiss as mere coincidence. For people who took melatonin on a long-term basis, the risk of developing heart failure was significantly higher: about 90% higher than for non-users. And not only that. Hospitalizations related to heart problems were much more frequent and the probability of dying from any cause was almost doubled among melatonin users. Numbers that, at first glance, clearly seem to overturn the mainstream perception of a harmless supplement.

Admittedly, the authors of the study admit, this is preliminary data, so these results should be taken with caution. And yet they are enough to raise doubts about this popular 'natural' remedy, both in American drugstores and in our pharmacies.

But scientific reality is never as straightforward as it might appear at first sight, and an observational study, even one on large numbers such as this one, cannot give any indication of a possible cause-and-effect relationship (melatonin - heart failure), let alone the pathogenic mechanisms behind it. It is therefore the authors themselves who urge caution: however substantial, this is a preliminary study, which has only been presented at an important congress but has not yet been published in full, nor has it been subjected to the caudine of peer review. This study only indicates a correlation, not a proven proof of a cause-effect relationship. In other words, we cannot say that it is melatonin that causes these effects on the heart. There could be confounding factors that contributed to this result; for example, those who suffer from severe insomnia may be more prone to use melatonin and may already be more susceptible to cardiovascular problems, perhaps because they suffer from anxiety, depression or other mental health conditions with a negative impact on the heart. Melatonin, in this scenario, would be more of a signal, a red flag, an alarm of an underlying phenomenon (the negative effect of poor mental health on the heart), than a cause.

And then there is another outstanding question, perhaps the most important: is melatonin always bad for you or does it depend on how long you use it? When taken for short periods and in particular situations (against 'geographical' jet lag or from shift changes, against temporary phases of insomnia) its use is generally considered useful and relatively safe. The problem arises when the exception becomes the rule, i.e. when the intake of melatonin supplements is prolonged for months or years, completely escaping the doctor's control.

And here two often underestimated aspects come into play. The first is the lack of solid data on the long-term safety of melatonin, especially with regard to its effects on the cardiovascular system. The second has to do with the nature of supplements themselves: in many countries they are not regulated as strictly as drugs, which means that dosages, purity and quality can vary considerably from one product to another. What we take every night before going to bed may not always be the same thing, with the same dosage and bioavailability, and it may also be a product that is not perfectly controlled.

The take-home message of this preliminary study, which nevertheless had the merit of uncovering Pandora's box, is therefore not to demonise melatonin tout court, but to downgrade its image as a good, natural and safe ally of sleep. Melatonin is not a magic wand, nor a universal, 'one-size-fits-all' solution. And it may not be entirely risk-free just because it is sold as a 'natural' remedy. Sleep, the real kind, is the result of a complex balance, made up of healthy habits, regular rhythms, the right environment and mental health. Perhaps, therefore, rather than looking for 'natural' shortcuts, it is worth asking yourself a few more questions. Better if together with your doctor.