Vitamins and minerals
Determining just how much of various vitamins and minerals people need for good health is a tricky science. For more than half a century, federal recommended dietary allowances (RDAs) spotlighted a combination of nutrients aimed at preventing deficiency diseases in most people. But the dietary reference intakes (DRIs) from the Institute of Medicine, which replaced the familiar RDAs, ushered in considerable change. Whereas the RDAs were established to prevent deficiency diseases, the DRIs seek also to enhance health and lower the risk for chronic conditions such as heart disease and cancer. This shift in focus reflects the fact that few people in industrialized countries today are deficient in nutrients, but many die from major diseases that could be prevented with better diets. The guidelines acknowledge that the need for certain nutrients varies with people's age, sex, and other important characteristics.
There are 13 vitamins, 16 minerals, and one additional dietary component that your body needs but cannot manufacture in sufficient amounts. Acting in concert, these essential vitamins and minerals help keep billions of cells healthy and encourage them to grow and reproduce. Some supply the keys to unlocking the energy in the carbohydrate, fat, and protein in the foods you eat. These essentials are often called micronutrients because your body needs only tiny amounts of them. Yet failing to get even those small quantities virtually guarantees disease. Old-time sailors learned that living for months without fresh fruits or vegetables — the main sources of vitamin C — causes the bleeding gums and listlessness of scurvy. In some developing countries, people still become blind from vitamin A deficiency. And even in the United States, some children develop the soft, deformed bones of rickets because they don't get enough vitamin D.
While the absence of key micronutrients hampers good health, their presence in sufficient quantities promotes it. Getting a full complement of iron helps proteins in your blood and muscles pick up and release the oxygen that's vital to all of your cells. It also fends off the absorption of lead, a heavy metal that can cause widespread damage. The B vitamin folic acid can be a powerful agent in protecting against birth defects and may help ward off heart disease and some forms of cancer. And a combination of calcium, vitamin D, vitamin K, magnesium, and phosphorus protects your bones against fractures.
Many of these micronutrients interact with one another. Vitamin D enables your body to pluck calcium from food sources passing through your digestive tract. Vitamin C helps you absorb iron. Vitamins and minerals differ in basic ways. Vitamins can be broken down by heat, air, or acid. Minerals are chemical elements that do not change. That means the minerals in soil and water easily find their way into your body through the plants, fish, animals, and fluids you consume. But it's tougher to shuttle vitamins from food and other sources into your body because cooking, storage, and simple exposure to air can inactivate these more fragile nutrients.
