Last week, the US Food and Drug Administration received a report detailing the results of the first major investigation into how the dietary supplements market should be regulated. And the conclusions, from the Institute of Medicine, are stark.

Most people assume that the vitamin A, B, C or D, or iron, selenium, manganese or cod liver oil, or ginseng, Ginkgo biloba or St John’s wort they swallow has been rigorously tested by government and declared harmless. It has not. And evidence is mounting that many of these products contain ingredients that can kill, especially if taken alongside certain prescription drugs.

There are almost no figures on the efficacy or toxicity of the 29,000 dietary supplements sold in the US in a market worth $18 billion a year. Many supplements, including traditional remedies, have been reformulated so often, and put to such a wide variety of uses, that no one knows for sure if they are still safe.

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