Choosing a Multivitamin

Understanding RDA, DV, DRI and UL

Multivitamin ingredients are measured in terms of the daily value (DV). The recommended amount of each vitamin and mineral is established by the FDA and is based in part on the recommended dietary allowances (RDA). Experts say that you should look for a multivitamin that provides 100 percent of the DV for most of the essential vitamins and minerals in one pill. The exception is calcium, which is too large to fit in one pill.

To add to the confusion, RDA and DV are used concurrently to describe nutrient recommendations. According to Erin Dummert, registered dietitian and president of Madam Nutrition LLC, the recommended daily allowance is the basic amount of a nutrient needed to meet the daily basic needs of healthy people. The RDA is one of the factors used to determine daily values, which are the amounts recommended to help prevent against disease -- those amounts are often higher than the RDA. The DV is what's presented on food labels, and the RDA is mainly used by health professionals. Consumers should consider the DV percentage as a guideline, Dummert says. This value indicates that the food has a certain percentage of the DV for each nutrient.

The newest standard for nutrient requirements is dietary reference intake (DRI). The DRI system is developed by the U.S. National Academy of Sciences' Institute of Medicine in consultation with Health Canada and is used in both countries. The DRI recommendations are made up of three components: the estimated average requirements (EAR), a level nutritionists say should meet the needs of 50 percent of the people in a defined age and gender group; the RDA or, where no RDA has been established, the adequate intake (AI); and the upper limit (UL), meaning the highest level that experts consider to be safe.

If all that leaves you confused, you're not alone. Even among research and nutrition professionals, there's considerable debate about optimal levels and safe upper limits. Part of the problem is that researchers don't yet understand completely how these substances work in the body.

Nutrients in the news

Some research is so well established that it doesn't provoke much controversy. Experts agree, for instance, that women who get at least 400 mcg of supplemental folic acid, or folate, per day are less likely to have a baby with a neural tube defect. Because the neural tube develops before most women know they're pregnant, experts recommend that all women of childbearing age include a folate supplement as part of their daily routine. Although it's still important to eat a balanced diet including natural folate sources like whole grains and leafy greens, nutritionists say this is one case where supplementation is prudent.

That's not always the case. According to the Institute of Medicine, vitamin A is critical for immune function, normal vision, gene expression, reproduction and embryonic development, but high supplemental vitamin A doses, especially if they're in the form of retinol, can cause problems. Medical studies published in the New England Journal of Medicine and other sources have found that taking more than 100 percent of the DV of vitamin A can cause some birth defects, and it can contribute to hip fractures in postmenopausal women. The current RDA for vitamin A is 3,000 international units (IU) for men and 2,310 IU for women. Although the official UL is higher, most health experts say it's best for adults to choose a multivitamin with no more than 5,000 IU of vitamin A with at least some of it in the form of beta-carotene. The Linus Pauling Institute at Oregon State University recommends that supplements with 5,000 IU of vitamin A have at least 50 percent from beta-carotene.

Beta-carotene, found naturally in a variety of plant foods, such as carrots and pumpkin, belongs to a family of nutrients called provitamin A carotenoids, which the body can convert into vitamin A. Because of the risks associated with excessive retinol supplementation, some nutritionists recommend beta-carotene. Even that isn't without risk. According to the Berkeley Wellness Letter, a study called the Carotene and Retinol Efficacy Trial (CARET) found that people at high risk for lung cancer -- smokers, former smokers and asbestos-industry workers -- were actually more likely to be diagnosed with lung cancer when they took beta-carotene supplements. Experts advise smokers to avoid taking beta-carotene supplements. However, eating foods rich in beta-carotene has the same potential benefits as supplementation without the risk of negative side effects.

There's also a lot of controversy around vitamin E. The RDA for vitamin E is 22.4 IU (15 mg) for people over the age of 14; the one exception is lactating women, who should get 28.4 IU (19 mg) per day. Some experts recommend doses exceeding the RDA, but others caution that the jury is still out on the long-term risks and benefits of vitamin E in supplement form. At the heart of the issue is a well-publicized 2004 meta-analysis from Johns Hopkins University that linked daily vitamin E intakes over 400 mg with a slightly elevated risk of premature death. According to the Berkeley Wellness Letter, however, three separate studies have since failed to confirm the Johns Hopkins findings, suggesting that vitamin E supplementation doesn't pose an increased risk of premature mortality. The National Institutes of Health confirms that studies on vitamin E have had conflicting results, and they think further research is needed.

The Institute of Medicine places the upper limit for vitamin E at 1,500 IU (1,000 mg) per day for adult men and women. The National Institutes of Health cautions that high doses of vitamin E in supplement form are linked to hemorrhage and stroke, but vitamin E from food does not appear to have the same effects. Because there is such a wide range between the RDA and upper limits for vitamin E, there's little consensus about the perfect dose for adults. The Linus Pauling Institute at Oregon State University recommends that adults take a supplement containing 200 IU of vitamin E each day, but the authors of the Berkeley Wellness Letter recommend getting your vitamin E from food, including "nuts, seeds, vegetable oils, whole grains, and leafy greens," rather than supplements. Your best bet is to ask your doctor about his or her recommendation.

Vitamin D is a different matter, because it's almost impossible to get enough from food sources -- you'd need to drink a quart of fortified milk per day or eat more than the recommended amount of fatty fish like salmon or tuna. The best source of this vitamin is sunlight, and research indicates that many Americans do not get enough time in the sun to ensure proper vitamin D levels. A study published in the Aug. 3, 2009, issue of the journal Pediatrics finds that 9 percent of American children are deficient in vitamin D, and 61 percent have insufficient levels of the vitamin. The study also says that children with vitamin D deficiency have higher blood pressure and lower HDL cholesterol than children with adequate levels of the vitamin. Experts, like those at the Harvard School of Public Health, say that 15 minutes of daily sun exposure -- without sunscreen -- is enough for most people to obtain adequate levels of vitamin D. However, the American Academy of Dermatology recommends that people meet their daily requirement with food and supplements rather than sun exposure, because of the risk of skin cancer. The Harvard School of Public Health says African-Americans, senior citizens and those who live in northern latitudes should ask their doctor if they need a vitamin D supplement.

The current AI for vitamin D is just 200 IU for adults younger than 50, 400 IU for people between 50 and 70 years old, and 600 IU for everyone older than 70. However, some experts recommend more, including the National Osteoporosis Foundation. It recommends that adults under the age of 50 get 400 to 800 IU per day; over 50 800 to 1,000 IU daily. The Harvard School of Public Health recommends at least 1,000 IU of vitamin D per day. Too much vitamin D can be toxic and lead to problems such as kidney stones, but Harvard says that adults can safely take up to 2,000 IU per day.