Because vitamin D insufficiency can be harmful to health,1- 3 supplementation is often prescribed. However, the Food and Drug Administration (FDA) does not regulate vitamin D supplements, so potency may not be well evaluated. In a recent trial examining vitamin D in menopausal women, we found that compounded vitamin D3 (cholecalciferol) supplements varied significantly in potency. Only one-third of our compounded study pills met US Pharmacopeial (USP) Convention standards, which require that compounded pills contain 90% to 110% of the active ingredient.4 This variability in compounded cholecalciferol pills led us to additionally investigate over-the-counter (OTC) cholecalciferol pills, in which we also found variability.
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I agree that supplements with a narrow therapeutic window, such as Vitamin D3, require stringent manufacturing procedures. Increased regulation isn't necessary. What is necessary is enforcement of existing cGMPs. Old regulations state 90-110% of label claim is acceptable. The current regulations require a product to have 100% of the label claim at the end of the expiration date. Consumers can ask a manufacturer for test results, including third party test results for each batch of each product. If it's not given, get the product from another company. There are a few, including DrTheos.com, who provide such information. You can also ask for shelf-life/stability testing. This exceeds the standards for OTC and Pharma drugs. No one should have to guess that the product they take meets label claims, nor assume that USP or another certifying organization is assuring that every batch checks out (because they don't). Furthermore, supplements should not have to have regulations that exceed drug manufacturing standards. The same testing information should be available to consumers of OTC and prescription drugs. Perhaps this would improve safety and help prevent some of the recalls we've seen in the industry.
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