The Dosage Of Multivitamins

A good multivitamin can support a healthy, balanced diet to make sure your body gets all the nutrients it needs. However, it can be hard to know which multivitamin to choose. Although most commercially available multivitamins are safe, your doctor can help you make the right choice based on your age, sex and health history. Be cautious of any multivitamin that offers megadoses of nutrients, which can be unnecessary or even harmful.

Recommended Daily Values and Dietary Reference Intakes

The government's recommended daily values, or DVs, on which most multivitamins and other supplements base their formulas haven't budged since they were set in 1968 by the National Academy of Sciences. Most multivitamins contain at least the DVs of their ingredients. In the mid-1990's, the DRIs, or Dietary Reference Intakes, replaced the Recommended Dietary Allowance, or RDAs, set in the 1960s. DRIs are closer to the mark because they take age and gender into account, and they recommend different levels for people with different concerns such as pregnancy and breastfeeding. However, the FDA still requires supplement labels to carry the older DVs, which don't take an individual's specific needs into account, making it especially important to seek a doctor's guidance when choosing a multivitamin.

Women

Many women who take a multivitamin get too much vitamin A, since it is available in so many foods. Excess vitamin A may lead to a risk of birth defects and problems with the liver and nervous system. Richard Laliberte reports in "Women's Health" magazine (December 2009) that many women get insufficient dietary vitamin D and calcium, but most multivitamins don't contain enough of either to address the lack, so an additional supplement may be necessary. In fact, no multivitamin contains the DRI for calcium -- 1,000 to 1,200 mg daily -- since the pill would be much too big to swallow. Premenopausal women should look for a multivitamin that contains 18 mg of iron. Adequate folic acid is essential for pregnant women, since it helps protect against birth defects. If you are pregnant, ask your doctor which multivitamin is right for you.

Men, Senior Citizens and Children

Men often need less iron supplementation than women. They may need 3,000 IU of vitamin A, as opposed to 2,300 for women, as well as 90 mg of vitamin C instead of 75 mg, and 120 micrograms of vitamin K instead of the women's recommendation of 90. The DRI for adult males is also higher than females in magnesium, zinc, and other minerals. Children's needs may be particularly difficult to gauge, since they can be picky or inconsistent eaters, and the DRI varies from year to year of a child's life. Children who eat little meat may need an iron or B-12 supplement, while children who don't eat much dairy may need additional vitamin D or calcium. If you are over the age of 50, your DRI may change considerably. Consult the Dietary Reference Intakes tables provided by the Institute of Medicine and speak with your doctor to determine the right dosages for any age.

Other Considerations

It can be difficult to get enough of certain nutrients in your everyday diet. These notably include folic acid, vitamin B-12, vitamin D and iron. The DRI for folic acid is 400 micrograms a day for both men and women, and for vitamin B-12, it's 2.4 micrograms. For vitamin D, the recommendation is 200 to 600 IU. Men should take 8 mg a day of iron, while women need 18 mg. Some health conditions or nutritional deficiencies may also call for additional supplements, but you must consult a medical professional for diagnosis and recommendations.