Making Sense of Vitamins and Minerals: Choosing the foods and nutrients you need to stay healthy

Cast of characters: From vitamin A to zinc

This chapter features a broad overview of the best-known vitamins and minerals. For each nutrient described in this section, you’ll find this information:

• The Recommended Dietary Allowance (RDA) or adequate intake (AI) for people ages 19 and older (with gender and age differences noted when applicable) and a brief description of the nutrient’s role in the body.
• A table of selected food sources containing the nutrient, with an emphasis on the best sources in commonly consumed foods. You can also search the U.S. Department of Agriculture (USDA) National Nutrient Database for Standard Reference, at www.nal.usda.gov/fnic/foodcomp/search/, to see exhaustive lists of foods organized by nutrient content.
• A summary of the data linking the nutrient to different health conditions. If a condition is not listed, that means there is insufficient evidence to support a connection between the nutrient and the disease.
• A recommendation about taking the nutrient in supplement form.

As a rule, your best strategy is to get vitamins and minerals from foods, not supplements. A vast amount of research has shown that you can cut your risk for chronic disease and disability by following a healthy diet, as well as exercising regularly and avoiding smoking. The evidence for taking vitamin and mineral supplements is much less convincing.

Keep in mind that these nutrients, while important, are simply one part of an overall plan for good health. Use them along with other well-established health care recommendations and treatments, not in lieu of them. If you’re worried about lung cancer, for example, quitting smoking will have a much greater impact on your health than taking supplements. Before taking more than a daily multivitamin supplement, discuss your decision with your doctor. Your medical history, genetic profile, and medications may affect the doses and types of supplements you can safely take.

Vitamin A and carotenoids

Men: 900 mcg (3,000 IU)
Women: 700 mcg (2,333 IU)

“Eat your carrots, they’re good for your eyes!” This oft-heard advice is rooted in truth: carrots and other colorful fruits and vegetables are rich in pigments known as carotenoids. Some carotenoids, such as beta carotene and alpha carotene, are known as provitamin A carotenoids, because they can be converted to vitamin A in the body.

The most usable form of vitamin A, retinol, is essential to the proper function of the retina, the light-sensitive tissue lining the back of the eye. In addition to its role in healthy vision, vitamin A also aids bone growth and helps regulate the body’s infection-fighting abilities. People in the United States obtain one-quarter to one-third of their vitamin A from provitamin A carotenoids—most commonly from carrots, cantaloupes, sweet potatoes, and spinach. There is no RDA for beta carotene or other provitamin A carotenoids, but 3 to 6 mg is equivalent to 833 to 1,667 international units (IU) of vitamin A—the amount that will keep blood levels in a range linked to a lower risk of chronic disease, according to the IOM.

Animal-based foods, including liver, milk, and eggs, contain preformed vitamin A, which makes up the bulk of the vitamin A in the average adult’s diet. Most fat-free milk and dried nonfat milk solids are fortified with vitamin A to replace the amount lost when the fat is removed. Many breakfast cereals are also vitamin A–fortified. According to the National Health and Nutrition Examination Survey (NHANES), a long-running study of the health status of Americans, the average adult in the United States gets 3,300 IU of vitamin A daily—well above the RDA for both men and women.