To the Editor This letter is in response to the Research Letter by LeBlanc et al1 about vitamin D in dietary supplements. As scientists at the Agricultural Research Service of the US Department of Agriculture (USDA) and the Office of Dietary Supplements of the National Institutes of Health (NIH), we are also concerned about the variability and content of ingredients in dietary supplements. Results of our work show similar variability in vitamin D content among products and sometimes among lots of multivitamin and mineral (MVM) supplements. Overall, we find that most MVM products have vitamin D overages but with considerable variability. The mean percentage difference for vitamin D tested in a pilot study of 54 adult MVM products was +17% of the label (range, +172% to −93%).2 The predicted mean percentage difference from the label using weighted regression techniques for a national sampling of 64 children’s MVM products was +34%3 (range, +110% to −38%). This variability is higher than that reported by LeBlanc et al1 and may be due to the multiple matrices evaluated by the USDA (MVM products were defined as supplements with >3 vitamins) and a larger national sampling of MVM products for these studies that included multiple channels.
Andrews KW, Pehrsson PR, Betz JM. Variability in Vitamin D Content Among Products for Multivitamin and Mineral Supplements. JAMA Intern Med. 2013;173(18):1752-1753. doi:10.1001/jamainternmed.2013.8759