Q. You wrote recently about the dangers of taking melatonin for insomnia, especially in large doses. In the study you cited, more people taking this pill had heart failure.

The dose might not be quite as high as it seems, though. According to a study of bioavailability, the amount of melatonin actually absorbed by the body is only about 3% (BMC Pharmacology & Toxicology, Feb. 19, 2016). In that light, the large oral tablet doses are not quite as scary as you implied.

People take melatonin because they have difficulty sleeping. Those who don’t sleep well are at significantly higher risk of heart attacks or death. That alone might explain the higher rates of heart failure among people taking melatonin.

A. Thank you for highlighting the study of oral melatonin bioavailability. We didn’t ap

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