Vitamin D supplements may contain doses that bear no relation to how they are labelled, a US study has found.
Tests on supplements from 12 manufacturers showed potencies ranging from 9-146 per cent of advertised amounts. Not only was there variation between brands, but also among different pills from the same bottle.
Lead author Erin Le Blanc, from the Kaiser Permanente Centre for Health Research in Portland, US, 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.”
For the research, published in the journal Jama Internal Medicine, an independent US laboratory was asked to analyse pills from 55 bottles of over-the-counter supplements. The pills were bought from five outlets in Portland, Oregon.
Some supplement manufacturers participate in a voluntary “kitemark” programme in America operated by the US Pharmacopeial Convention (USP). To obtain USP verification manufacturers agree to have their products tested for quality, potency and purity.
The study found that pills from a USP-marked bottle were generally more accurately described than others tested.
In the European Union, accurate labelling of vitamin and mineral supplements is a legal requirement under the 2002 European Union food supplements directive.