In northern climes, the winter sun is too weak for people to generate vitamin D on their own, and it can be hard to get enough in food. iStockphoto hide caption

In addition to heart problems triggered by some supplements, emergencies often arise when kids swallow dietary supplements meant for adults, according to the CDC analysis, or when older adults choke on the pills. Lee Woodgate/Ikon Images/Corbis hide caption

Ideally, we'd all eat super healthful diets. But that's not the world we live in, and multivitamins may help bridge the nutritional gaps. Jasper White/Getty Images hide caption

The Original Grape-Nuts, which now bear a non-GMO label, no longer contain vitamins A, D, B-12 and B-2. Claire Eggers/NPR hide caption

Vitamin E for your heart? Don't bother, new guidelines say. iStockphoto hide caption

Though some people might need more of specific vitamins, multivitamins don't help most people, studies say. iStockphoto hide caption

If only it was as simple as popping a supplement and being set for life. But alas, no. iStockphoto.com hide caption

Ads often tout dietary supplements and vitamins as "natural" remedies. But studies show megadoses of some vitamins can actually boost the risk of heart disease and cancer, warns Dr. Paul Offit. iStockphoto.com hide caption

In Washington's Columbia Heights neighborhood, Claire Robertson, a grad student, talks with Scott Hensley about retail health clinics. David Schultz/NPR hide caption

Pfizer will drop or qualify some health claims on labels and in ads for Centrum vitamins and supplements. CSPI hide caption