The National Institutes of Health says there's no reason to recommend multivitamins in general but notes a few combinations that might help some people, such as beta-carotene, vitamins C and E, and zinc for those with age-related macular degeneration.

But multis can make sense for certain groups:

• Dieters or picky eaters, to prevent major nutritional deficiencies.
• Strict vegetarians, mainly for the vitamin B12.
• People older than 50, mainly for the B12 and vitamins.
• Women who are pregnant, likely to become pregnant, or breast-feeding.
• People who have a chronic gastrointestinal disorder, such as colitis or pancreatitis, that impairs absorption or digestion.
• People with a chronic illness. Diabetes, cancer, and other conditions can deplete nutrients.

So-called women's multis often pack extra calcium, which can be fine for both genders, but if you need more than 200 mg you'll have to take a separate calcium supplement. Stick with the basic nutrients: the herbs and phytochemicals sometimes included have dubious value and are often present in such small quantities that they have little effect. Finally, avoid supplements that contain more than 9 mg of iron unless advised by your doctor, since excess iron can lead to organ damage in people with hemochromatosis, a common genetic disorder.

This article first appeared in the September 2008 issue of Consumer Reports On Health.

Read more on special precautions (free) you should follow when taking a multivitamin, find out which vitamins fill your nutritional gaps and which you should avoid (free), and if you're taking a multivitamin or supplement, visit our Natural Medicine Ratings (subscribers only) section to check the effectiveness and interactions.