Melatonin Heart Failure Concern

Melatonin supplements have surged in popularity, with many products offering 5 mg or even higher doses. The speaker points out that endogenous production is an order of magnitude lower, and supplement bioavailability (~15%) means even a 1 mg dose results in exposure that can be several times the natural peak. While the scary observational study is flawed, there remains a gap in long-term safety trials for supraphysiological doses. The speaker therefore opts for a dose that sits ‘right in the middle of the range normally produced by the body’ (0.3 mg, yielding roughly 45 mcg absorbed). He explicitly states he would not take more than 1 mg per night. This approach balances the sleep benefits demonstrated in meta-analyses (reduced sleep onset latency, improved sleep quality) with a conservative safety margin until robust long-term data emerge.

The speaker emphasizes that melatonin's primary action is chronobiotic—it resets the internal clock rather than simply inducing drowsiness like a sleeping pill. For it to work optimally, the timing relative to the desired sleep phase is critical. Taking it about 2 hours beforehand gives the hormone enough time to act on the suprachiasmatic nucleus and gradually shift the sleep-wake cycle forward. This advice is often overlooked, and many people take melatonin right at bedtime, which may limit its benefits.

The researchers formed two groups: those with a prescription for melatonin in their records (melatonin group) and those without any mention of melatonin (non-melatonin group). Because the TriNetX database includes data from many countries where melatonin is prescription-only (e.g., UK) and others where it is over-the-counter (e.g., USA), anyone taking OTC melatonin would not have a prescription record and thus be misclassified into the non-melatonin group. This contamination makes any comparison between the groups meaningless. Moreover, as an observational study, it can only show association, not causation. The classic ice cream sales and shark attacks analogy illustrates how correlated variables may share a common cause (summer). In this case, people with more severe insomnia are more likely to seek a prescription for melatonin, and it is well established that insomnia itself increases heart disease risk through elevated inflammation. The study found melatonin users had an 89% higher rate of new heart failure, over 3x the rate of heart failure hospitalizations, and roughly 2x higher all-cause mortality, but all of these could be driven by the underlying sleep disorder rather than the supplement.

A 2025 meta-analysis of four RCTs in patients already diagnosed with heart failure found that melatonin improved patient scores on a heart failure measure, significantly boosted quality of life, and increased an important metric of blood vessel health. There was also a trend towards improvement in the heart's pumping ability (ejection fraction), though it did not reach statistical significance. These human RCT findings align with a broader 2022 review summarizing evidence from both human and animal studies showing melatonin protects the heart. Thus, the weight of experimental, causal evidence leans toward a beneficial effect, not harm.