An analysis of 55 products from 12 manufacturers found that the actual vitamin D content of the supplements varied among different brands, manufacturers, and even among different pills from the same bottle.
“In our test, just over one-half of OTC pills and only one-third of compounded vitamins met USP Convention standards,” report researchers from the Kaiser Permanente Center for Health Research in Portland, Ore. and Eagle Analytical Services in Houston.
“Lack of accuracy in cholecalciferol dosing may not cause harm in most consumers. However, supplementation may be less effective and dose adjustments inaccurate in inconsistent users, which may harm women with severe vitamin D deficiency.”
On the other hand, the researchers said that products that are USP verified may have “better accuracy” and the vitamin D content may be “less variable”.
Erin LeBlanc, MD, lead author and investigator with Kaiser Permanente said: “The USP verification mark may give consumers some reassurance that the amount of vitamin D in those pills is close to the amount listed on the label,” she added.
“There are not many manufacturers that have the USP mark, but it may be worth the extra effort to look for it.”
John Atwater, PhD, director of USP verification programs, told NutraIngredients-USA: “The recent findings by the Kaiser Permanente Center for Health Research regarding the highly variable potency of Vitamin D supplements impacts consumer trust in the quality of dietary supplements.
"Certainly, we are pleased, but not surprised, that a USP Verified product performed well in this type of study. As consumers become more discerning in choosing which dietary supplements they purchase for themselves and their families, manufacturers who want to demonstrate quality may see significant value in third-party verification from trusted organizations such as USP.”
Cluster of products that are ‘spot on’
Commenting on the letter’s findings, Duffy MacKay, ND, vice president of scientific and regulatory affairs for the Council of Responsible Nutrition (CRN), told us: “Dietary supplements are very well regulated, and the regulations include what’s on the label.”
“At first glance, there are no excuses for products to not meet label claims,” he said. “On deeper analysis, half the samples were analyzed at an external lab, and therefore many of results come in within the 10% variability that you get between labs.
“Any of the products that are between 85% and 110% of the content may in fact be spot on when you consider the 10% variability.
Indeed, 7 of the 12 manufacturers’ products approximately cover this range. “So what you have is a cluster of products that were spot on, and that was not considered in the letter.”
Dr MacKay added that the analysis does not raise any safety concerns. “For a product with 1,000 IUs, if the content is between 50 and 135%, then you are looking at supplements containing 500 IUs and 1,350 IUs. There are no safety concerns here.
Good for the industry
“Philosophically, this kind of article is a good thing because it means that the medical community is taking vitamin D seriously. They understand the benefits, they are reassured of the safety, they are testing for it, and physicians are prescribing it,” said Dr MacKay.
“The medical establishment is embracing nutrition and I think we will see a lot more of this kind of analysis.”
Source: JAMA Internal Medicine
Published online ahead of print, Online First, doi: 10.1001/jamainternmed.2013.3812
“Over-the-counter and compounded vitamin D: IS Potency What We Expect?”
Authors: E.S. LeBlanc, N. Perrin, J.D. Johnson Jr., A. Ballatore, T. Hillier,