The website of the National Institutes of Health’s Office of Dietary Supplements addresses such issues.
An extensive dictionary demystifies commonly used terms. (Yes, it includes abetalipoproteinemia — a rare disease in which the intestine can’t absorb fat. People with the disorder require huge amounts of vitamin E, though the rest of us could be harmed by too much of the vitamin.) Consumer updates help make sense of which products could present risks. There’s also information on how supplements are regulated and how manufacturers may legally make claims about their products.
The most useful materials on the site are fact sheets on products such as magnesium and folate. The sheets explain whether the substances are necessary and highlight research on their health effects. (The site refers visitors looking for information on herbal supplements such as garlic and ginkgo to the National Center for Complementary and Integrative Health, which offers similar fact sheets.)
The site sounds a similar note in nearly all of its communications: It’s usually best to use food, not pills, as your source of vitamins and minerals. That message might save you a bit of money — or at least make you somewhat more skeptical the next time you stroll down the supplements aisle.