The Centers for Disease Control and Prevention reports that only a quarter of Americans eat the recommended number of vegetables every day and that only a third consume enough fruit. "The reason they're called vitamins is that they're vital to life, yet 92 percent of Americans are deficient in one or more essential vitamins and minerals because they don't eat enough fruits, vegetables, and other whole foods," says Mark Hyman, chairman of the Institute for Functional Medicine. While there's little research showing that multivitamins can treat specific diseases, Weil says the supplements can be important as a type of nutritional mortar, filling in the chinks caused by a less-than-perfect lifestyle.
How to take them: Scan labels to check if a multi contains 100 percent of the RDA of the 21 essential nutrients: vitamins A, C, D, E, K, and B (including thiamin, riboflavin, niacin, B6, B12, pantothenic acid, biotin, folate, and choline) and minerals calcium, chromium, copper, fluoride, iodine, iron, magnesium, manganese, molybdenum, phosphorous, selenium, zinc, potassium, sodium, and chloride. A quicker screening method, says Dowd, is to look to see if a multi has 100 percent of the RDA for vitamin K. Most don't, so if you find one that does, it's usually a good bet.
Only so many nutrients can fit into a multivitamin, so if a pill contains everything from açai to zeathanthin, chances are it doesn't have adequate dosages of every ingredient, says Andrew Shao, senior vice president of scientific and regulatory affairs for the Council for Responsible Nutrition. Instead, stick mainly to the essentials and don't go too high above the Daily Value (DV). "Some companies put in an absurd number of nutrients when there is no data to support it," says Steven Kaplan, director of the Iris Cantor Men's Health Center at New York-Presbyterian Hospital/Weill Cornell Medical Center. "Most of those ingredients just wind up in the toilet, literally, because your body doesn't need that much." That said, don't look to your multi for adequate vitamin D. If a multi provides less than 1,000 IU – and most do – you'll still need a D supplement.