The potency of vitamin D supplements varies widely from what is advertised on the label, according to a study of 12 vitamin manufacturers.
Researchers conducted a recent trial examining vitamin D in menopausal women and found that vitamin D3 supplements varied significantly in potency. Only a third of the study supplements met US Pharmacopeial (USP) standards, which require that supplements contain 90 – 110% of the active ingredient.
“This variability in compounded cholecalciferol pills led us to additionally investigate over-the-counter (OTC) cholecalciferol pills, in which we also found variability,” they explain.
Erin S LeBlanc, MD, MPH, and colleagues randomly selected 5 pills each from 15 sealed bottles of vitamin D3 purchased at 5 stores in Portland, Oregon.
They found that the over-the-counter supplements contained 52% to 135% of the advertized dose. The authors explain, “When averaged over 5 pills, two-thirds of bottles met USP Convention standards for OTC cholecalciferol [vitamin D3] solution…” In a quarter of the bottles, all 5 pills met the USP standards.
The researcher’s also analyzed vitamin D3 compounded study pills (1000 IU and 50,000 IU). They found that the 50,000 IU pills contained 52-105% of the advertised dose. The 1000 IU tablets contained 23-146% of the expected dose.
“In our test, just over one-half of the OTC pills and only one-third of compounded pills met USP Convention standards,” they continue.
The authors conclude that lack of accuracy most likely won’t harm anyone taking the supplements, although it will influence effectiveness. They also point out that inconsistency in dosage from pill to pill may influence vitamin D trials using compounded supplements to raise vitamin D levels.
The authors conclude that they agree with calls to increase regulation of dietary supplements.