Vitamin D insufficiency can be harmful to health, hence supplementation is commonly prescribed. However, vitamin D supplements are not regulated by the FDA, meaning that potency might not be evaluated.
In a Research Letter in the journal, the authors explained that vitamin D supplements can have as little as 9% and as much as 146% of what their labels claim. Variations exist not only from brand-to-brand and bottle-to-bottle, but also from pill-to-pill within the same bottles in some cases.
Erin S. LeBlanc, MD, MPH, lead author, from the Kaiser Permanente Center for Health Research in Portland, Oregon, said:
"We were surprised by the variation in potency among these vitamin D pills. The biggest worry is for someone who has low levels of vitamin D in their blood. If they are consistently taking a supplement with little vitamin D in it, they could face health risks."
The FDA (Food and Drug Administration) has been trying to tighten up the labeling of dietary supplements for many years - a market which is worth over $28 billion every year in the USA alone (combined vitamins, herbs and supplements).
USP verification markSome vitamin supplement manufactures say they take part in a voluntary quality verification program run by the US Pharmacopeial Convention, a not-for-profit organization which sets public standards for the quality of vitamin, mineral and other dietary supplements. They have to undergo annual GMP (good manufacturing practice) audits in order to get the USP verification mark. Their products are also tested for purity, potency and quality.
Dr. LeBlanc and team found that USP Verified vitamin D supplements were generally more accurate than the other containers they tested. They included one USP Verified manufacturer in their sample of supplements.
LeBlanc 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. There are not many manufacturers that have the USP mark, but it may be worth the extra effort to look for it."
The researchers tested:
- 55 bottles of OTC vitamin D supplements
- The products came from 12 different manufacturers
- They purchased the products at five different shops in Portland
- The compounded vitamin D was made by a Portland compounding pharmacy
Written by Christian Nordqvist