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). To add to the confusion, RDA and DV are used concurrently to describe nutrient recommendations. According to the National Institutes of Health, the recommended daily allowance is the 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 -- amounts often higher than the RDA. The DV is what's presented on food labels, and the RDA is mainly used by health professionals.

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 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 folic acid 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.

However, experts are split on the value of supplements for other nutrients. Vitamin D and calcium have both been in the news recently, and articles tout the possibility that these nutrients may prevent a variety of diseases, including cancer, multiple sclerosis and heart disease. In November 2010, the Institute of Medicine released new guidelines for calcium and vitamin D. For calcium, the Institute recommends 700 to 1,000 mg a day for children, 1,300 mg a day for adolescents and 1,000 mg a day for adults. Men over the age of 70 and women over the age of 51 should aim for 1,200 mg daily. The DRI for vitamin D has been increased to 600 international units (IU) for children and most adults, with the exception of those over the age of 70, who are recommended to get 800 IU daily.

However, the Institute concludes that most Americans are getting enough of both nutrients, with the exception of teenage girls, who tend to fall short on their calcium intake. Their experts say that supplements may be prudent only in limited cases, including for adolescent girls and seniors. Although the Institute says that vitamin D and calcium's role in bone health is clear, it maintains that the available evidence does not yet confirm other health benefits, including prevention against cancer and heart disease. They also warn of the dangers of excess calcium and vitamin D, including kidney stones and kidney damage. The new upper limit (UL) for adults has been established at 4,000 IU for vitamin D and 2,000 to 2,500 mg of calcium, depending on age. "People don't need more than the amounts established in this report," says Catharine Ross, the report committee chair.

Although the Institute of Medicine believes most Americans are getting enough vitamin D -- and its researchers evaluated more than 1,000 medical studies in reaching this conclusion -- not all experts agree. In fact, some recent studies show that vitamin D deficiency is a common problem. A February 2011 study published in Nutrition Research finds that more than 40 percent of American adults are deficient in vitamin D, with African-Americans and Hispanics being especially susceptible to deficiency.

Vitamin D is found in fortified milk and fatty fish, but it's hard to get enough of the vitamin from food alone. Your body produces vitamin D when exposed to UVB rays, but experts say that is an unreliable source. According to the National Osteoporosis Foundation, there are a variety of factors that influence how much vitamin D a person makes from sunlight, including their age, skin color, where they live and use of sunscreen. In addition, exposing unprotected skin to the sun's rays increases the risk of skin cancer. The American Academy of Dermatology argues that vitamin D should be obtained from food and supplements, not sunlight. Since experts are split on the value of vitamin D and calcium supplements, the best course of action is to talk to your doctor about your particular health needs.

Vitamin A is one nutrient that is essential for human health but that can cause adverse effects at high doses. 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, whether in the form of retinol or beta-carotene, 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 may contribute to osteoporosis and hip fractures in postmenopausal women, according to the National Institutes of Health. A major lung cancer study, the Alpha-Tocopherol Beta-Carotene Cancer Prevention Study, ended early when researchers discovered that those who took beta-carotene supplements were 46 percent more likely to die from lung cancer. However, eating foods rich in vitamin A, such as carrots, spinach and cantaloupe, has the same potential benefits as supplementation without the risk of negative side effects.

The current RDA for vitamin A is 3,000 IU for men and 2,333 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.

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. A study published in the January 2011 issue of Age and Ageing found that vitamin E supplements might extend the life span of men over the age of 71. On the other hand, a well-publicized 2004 meta-analysis from Johns Hopkins University 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 may not 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. 

For every study that links a supplement to a supposed health benefit, there is likely another study that links it to adverse health effects. So what's a person to do? Experts agree that getting your nutrients from whole foods is best -- you reap all the benefits of each individual vitamin without the risk of side effects seen when those same vitamins are taken in supplement form. The science on nutritional supplements is constantly evolving, but it is unlikely that a single dietary supplement or vitamin will ever be a silver bullet for our nation's health woes. Your best bet is to discuss with your doctor whether specific supplements or multivitamins are necessary for your individual health condition.