(HealthDay News) – The potency of over-the-counter (OTC) and compounded vitamin D (cholecalciferol) supplements vary widely, according to a research letter published online Feb. 11 in JAMA Internal Medicine.

Erin S. LeBlanc, MD, MPH, of Kaiser Permanente in Portland, OR, and colleagues assessed the vitamin D potency of OTC supplements (five pills from 15 sealed bottles of dietary supplements purchased at five stores from 12 manufacturers).

In analysis of the five pills from the same bottle, the researchers found that the potency of vitamin D was 52%–135% of the expected dose. <10% variability was seen in two-thirds of bottles. All five pills from the U.S. Pharmacopeial (USP)-verified manufacturer were within 10% of the expected dose. The potency of five pills taken from five bottles with the same lot number varied from 57%–138%, while those from different lot numbers ranged from 9%–140% of the stated dose. For the USP-verified manufacturer, the potency of pills from different lots was within 90%–120% of the expected dose. For the USP-verified manufacturer, the potency of the 1,000 IU pills was more variable (70%–140% of expected dose). For compounded 50,000 IU pills, only one-third of pills were within 10% of the expected dose.

“Lack of accuracy in cholecalciferol dosing may not cause harm in most consumers,” the authors write. “However, supplementation may be less effective and dose adjustments inaccurate in inconsistent users, which may harm women with severe vitamin D deficiency.”

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