Taking one can help fill nutritional gaps. Here's how to choose which is best for you.
Credit: Becky Luigart-Stayner

If you've ever tossed from the fridge weary vegetables that never made it to your plate, you're not alone. Despite our best intentions, healthy eating habits sometimes go astray. So, nearly 50 percent of adults use a daily multivitamin to pick up the nutritional slack in their diets, according to the American Dietetic Association (ADA). Most dietitians favor improving food choices over popping a pill, but they also understand the safeguarding benefits of a multivitamin. "Food and supplements are not mutually exclusive," says Marie Dunford, Ph.D., R.D., the author of Nutrition Logic: Food First, Supplements Second, who believes a multivitamin can "insure" you on days when healthful habits slide.

Yet, deciding if you need a multivitamin, or which one fits your needs, can be confusing. We've gathered answers to the most frequently asked questions about multis so you can spend less time in the supplement aisle and more time at the dinner table.

Q: I eat healthfully. Do I need a multivitamin?
"If you're healthy, not pregnant, and eating the minimum number of servings per day from the Food Guide Pyramid, you do not need a multivitamin," says Tara Geise, M.S., R.D., an ADA spokesperson. However, a survey from the United States Department of Agriculture shows that the diets of 74 percent of Americans fall short of the guidelines set forth by the food pyramid. For this reason, the ADA recommends that women of childbearing age, strict vegetarians, adults older than 60, and those who aren't consuming an optimal diet take a daily multi to boost nutrient levels. If you eat healthfully but still want to take a multivitamin, most dietitians agree it poses no risk, as long as you don't exceed 100 percent of the Daily Value of vitamins and minerals. Daily Values reflect the basic nutrition needs of a healthy person who requires 2,000 calories per day.

Q: Is taking more than 100 percent of the Daily Value safe?
Sticking to 100 percent or less is best. Consuming high doses of some vitamins, such as A, D, E, and K, can lead to side effects ranging from mild to severe. For example, high amounts of vitamin A-two to three times the DV-can cause liver damage or weaken bones, and excess vitamin B6 can lead to nerve damage. Others are simply excreted when you take in more than you need. Either way, there's no benefit to overconsumption.

Q: What is the difference between the RDA and the Daily Value?
The RDAS, or Recommended Dietary Allowances, are age- and gender-specific, and based on healthy people's needs. You'll find RDA charts in textbooks, but not on food labels. That's where Daily Values, which are found on vitamin labels, come in. Because Daily Values are not based on age or gender, they typically reflect the needs of the group that requires more, particularly for critical nutrients. For example, the RDA for iron is 8mg for men and 18mg for women. One hundred percent of the Daily Value for iron is set at 18mg.

Q: There are so many multivitamins on the market, how do I know which one is best?
Tens of thousands of dietary supplements are currently on the market, with about 1,000 new products added each year. While only some are considered multivitamins, the sheer number of products can be overwhelming. "Look for a multivitamin with the USP (United States Pharmacopeia) seal," Geise says. Dietary supplements, including multis, are not preapproved for quality before market release, so only this voluntary standard of quality exists. A product with the USP-verified mark ensures that the multivitamin contains the ingredients and amounts stated on the label, disintegrates properly for ideal absorption, and is free of contaminants. There appear to be no significant differences in quality between the USP-approved vitamins in the lowest and those in the highest price ranges.

Q: My multivitamin upsets my stomach. Is that normal?
This is a common side effect, particularly if a multivitamin contains iron. It doesn't really matter what time of day you take your vitamin, but taking it with food and a glass of water can help lessen stomach upset.

Q: Should men and women take different multivitamins?
In general, experts recommend that men avoid multivitamins with iron, not only because they require less, but also because consuming too much can be risky and cause damage to tissue and organs. Fortunately, women's multis are commonly tailored to meet the iron needs of women of childbearing age, and men's multi formulas typically exclude iron.

Q: Do specially formulated multivitamins with ingredients like green tea or lycopene offer added benefits?
If it doesn't have a recommended DV, it shouldn't be included in your vitamin. Some "bonuses" may do more harm than good. For example, studies from the American Heart Association suggest that taking antioxidants like beta-carotene in supplement form can actually increase disease risk, or at the very least, offer no protection. Researchers believe that antioxidants in foods work together to create a delicate balance. Taking high doses of a single antioxidant throws off this equilibrium, preventing each from doing its job properly. The benefits of drinking green tea or eating lycopene-rich tomatoes, on the other hand, look promising. Skip the extra supplements, and spend the money you save on natural antioxidant sources, such as bags of dried blueberries, cranberries, or soy nuts to stash in your purse or desk drawer. Avoid vitamins that address "special needs"-those for carb-restrictive diets or "active" lifestyles, for example. These are often the result of targeted marketing.

Q: Do multivitamins expire?
Yes. Just like foods and medications, multivitamins lose their potency over time. Keep your eye on the expiration date, which is usually about a year from the date of purchase, and be sure to store the bottle in a cool, dry place to maintain its shelf life. Store your vitamins in a spot that doesn't expose them to damaging heat and humidity and is out of reach to kids and pets. Then, take them when you need them.

Cynthia Sass, M.P.H., M.A., R.D., is a spokesperson for the American Dietetic Association and an adjunct professor of nutrition at the University of South Florida. She is also the author of Your Diet is Driving Me Crazy.