With added amino acids, antioxidants, enzymes and herbs, it might seem like dietary supplements could easily replace food as your source of nutrients. But this isn't the case. Whole foods — such as fruits, vegetables and whole grains — provide a complex combination of vitamins, minerals, fiber and other substances that promote health.

Though vitamin and mineral supplements can't copy all of the nutrients and benefits of whole foods, they can complement your diet. If you have trouble getting enough nutrients, you may benefit from taking a vitamin or mineral supplement. To use supplements safely, weigh your nutritional needs, scrutinize the merits of taking a supplement, and understand how to choose and use dietary supplements.

Vitamins and minerals are substances your body needs in small but steady amounts for normal growth, function and health. Together, vitamins and minerals are called micronutrients. Your body can't make most micronutrients, so you must get them from the foods you eat or, in some cases, from supplements.

Vitamins: Partners in regulating body functions
Vitamins are needed for a variety of biologic processes, among them growth, digestion, mental alertness and resistance to infection. They also enable your body to use carbohydrates, fats and proteins, and they act as catalysts — initiating or speeding up chemical reactions. Though vitamins are involved in converting food into energy, they supply no calories.

Vitamins can be either water-soluble or fat-soluble.

• Water-soluble vitamins. Vitamin C, biotin and the seven B vitamins — thiamin (B-1), riboflavin (B-2), niacin (B-3), pantothenic acid (B-5), pyridoxine (B-6), folic acid (B-9) and cobalamin (B-12) — dissolve in water (water-soluble) and aren't stored in your body in any significant amounts. Surplus water-soluble vitamins are simply excreted in your urine.
• Fat-soluble vitamins. Any extra vitamin A, D, E or K not used by your body right after ingestion is stored in your body fat and liver. Excess fat-soluble vitamins can accumulate in your body and become toxic. You're especially sensitive to excess amounts of vitamins A and D. Because vitamins E and K affect blood clotting, talk with your doctor before taking a supplement that contains either of these vitamins if you're taking a blood thinner, such as warfarin (Coumadin).

Minerals: Building blocks for your body
Minerals are the main components in your teeth and bones, and they serve as building blocks for other cells and enzymes. Minerals also help regulate the balance of fluids in your body and control the movement of nerve impulses. Some minerals also help deliver oxygen to cells and help carry away carbon dioxide.

Minerals have two categories:

• Major minerals. Calcium, phosphorus, magnesium, sodium, potassium, sulfur and chloride are considered major minerals because adults need them in larger amounts — more than 250 milligrams (mg) a day.
• Trace minerals. Chromium, copper, fluoride, iodine, iron, manganese, molybdenum, selenium and zinc are considered trace minerals because your body needs them in smaller amounts — fewer than 20 mg a day.

Whole foods are your best sources of vitamins and minerals. They offer three main benefits over supplements:

• Whole foods are complex. They contain a variety of the micronutrients your body needs — not just one. An orange, for example, provides vitamin C but also beta carotene, calcium and other nutrients. A vitamin C supplement lacks these other micronutrients.
• Whole foods provide dietary fiber. Fiber is important for digestion and can help prevent certain diseases such as cancer, diabetes and heart disease. Adequate fiber intake can also help prevent constipation.
• Whole foods contain other substances that appear to be important for good health. Fruits and vegetables, for example, contain naturally occurring food substances called phytochemicals, which may help protect you against cancer, heart disease, diabetes and high blood pressure. Many are also good sources of antioxidants — substances that slow down oxidation, a natural process that leads to cell and tissue damage. If you depend on supplements rather than eating a variety of whole foods, you miss the potential benefits of these substances.

Many people don't receive all of the nutrients they need from their diet because they either can't or don't eat enough, or they can't or don't eat a variety of healthy foods. For some people, including those on restrictive diets, multivitamin-mineral supplements can provide vitamins and minerals that their diets often don't. Pregnant women and older adults have altered nutrient needs and may also benefit from a supplement.

Supplements, as the term suggests, can complement your regular diet, but they aren't food substitutes. They can't replace the hundreds of nutrients found in whole foods. But if you do decide to take a vitamin or mineral supplement, consider these factors:

• Check the supplement label. Read labels carefully. Product labels can tell you what the active ingredient or ingredients are, which nutrients are included, the serving size — for example, capsule, packet or teaspoonful — and the amount of nutrients in each serving. The label also provides directions for safe use and tips for storage along with the name and address of the manufacturer, packer or distributor where you can write if you need more information on a particular product.
• Avoid supplements that provide "megadoses." In general, choose a multivitamin-mineral supplement — for example, Centrum, One A Day, others — that provides about 100 Percent Daily Value (%DV) of all the vitamins and minerals instead of one that supplies, for example, 500%DV of one vitamin and only 20%DV of another. The exception to this is calcium. You may notice that calcium-containing supplements don't provide 100%DV. If they did, the tablets would be too large to swallow. Most cases of nutrient toxicity stem from high-dose supplements.

• Look for “USP” on the label. This ensures that the supplement meets the standards for strength, purity, disintegration and dissolution established by the testing organization, U.S. Pharmacopeia (USP).
• Beware of gimmicks. Synthetic vitamins are usually the same as so-called "natural" vitamins, but "natural" vitamins usually cost more. And don't give in to the temptation of added herbs, enzymes or amino acids — they add mostly cost.
• Look for expiration dates. Supplements can lose potency over time, especially in hot and humid climates. If a supplement doesn't have an expiration date, don't buy it. If your supplements have expired, discard them.
• Store all vitamin and mineral supplements safely. Store supplements in a dry, cool place. Avoid hot, humid storage locations, such as the bathroom. Also, store supplements out of sight and away from children. Put supplements in a locked cabinet or other secure location. Don't leave them on the counter or rely on child-resistant packaging. Be especially careful with any supplements containing iron. Iron overdose is a leading cause of poisoning deaths among children.
• Play it safe. Before taking anything other than a standard multivitamin-mineral supplement of 100%DV or less, check with your doctor, pharmacist or a registered dietitian. High doses of some vitamins or minerals may cause health problems. For example, high doses of vitamin B-3 (niacin) can result in or worsen liver problems, and too much vitamin A over time may cause liver problems or weaken bones in women. In addition, supplements may interfere with your medications. For instance, vitamin E isn't recommended if you're taking blood-thinning medications (anticoagulants) because it can complicate the proper control of blood thinning. If you're already taking an individual vitamin or mineral supplement and haven't told your doctor, discuss it at your next checkup.