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 appreciate that only a small amount of melatonin is absorbed from a pill.
The research you cited shows that there is tremendous variability from one person to another. The authors report that prior studies found absorption between 9% and 33%.
A common dosing regimen is 3 milligrams of melatonin taken about one hour before bedtime. If people only absorb 3%, that equals a dose of 90 micrograms, roughly three times more than our bodies normally make in a day.
To learn more about melatonin and other ways to overcome insomnia, you may wish to read our “eGuide to Getting a Good Night’s Sleep.” This online resource can be found under the Health eGuides tab at www.PeoplesPharmacy.com
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In their column, Joe and Teresa Graedon answer letters from readers. Write to them in care of King Features, 628 Virginia Drive, Orlando, FL 32803, or email them via their website: www.PeoplesPharmacy.com. Their newest book is “Top Screwups Doctors Make and How to Avoid Them.”
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