The amounts of vitamin D present in supplements sold over the counter often bear little resemblance to the descriptions on the bottle labels, a new study concludes.
Researchers used high-performance liquid chromatography to analyze pills in 55 bottles of vitamin D bought at five stores in Portland, Ore. Their results were published online last week in JAMA Internal Medicine.
The Food and Drug Administration does not regulate the potency of vitamin D supplements, but companies may choose to comply with the standards of the United States Pharmacopeial Convention, which requires that pills contain 90 percent to 110 percent of the listed potency.
In pills from bottles made by a single manufacturer, but in different lots, the researchers found potencies as low as 9 percent and as high as 140 percent of the listed dose. They averaged the dosages of five pills from each bottle and found that only two-thirds met the U.S. Pharmacopeial Convention standard.
Pills from the bottle of the one manufacturer that was verified by the convention averaged 101.7 percent of the listed dosage, although
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