A recent study in the Archives of Internal Medicine reports that nearly half of Americans now take some kind of nutritional supplement. Yet studies also show that people often take supplements for nutrients they have already consumed in adequate amounts, and miss supplementing the nutrients they may lack. If you use or are considering a supplement, research identifies several considerations in making a good choice.

Surveys show that nearly half of all supplement users take a "multiple vitamin." Recent government nutrition recommendations suggest that for some people, particularly those over age 50, such products can help by supplying vitamin B-12 in a form that can be easily absorbed, and vitamin D that they might otherwise lack if they don't consume a quart of milk daily. Those over 50 who are not using cereals or supplements fortified with these nutrients should make sure their multiple vitamin supplies about 2.4 micrograms (mcg), or 40% of daily value of vitamin B-12, plus 400 international units (IU), or 100% daily value of vitamin D. Those over age 70 need a total of 600 IU of vitamin D (150% of daily value).

Many supplements supply variable amounts of vitamins and minerals. A supplement with 25 to 100 percent of daily value for zinc and magnesium is reasonable for many people. But iron is a little more complicated. According to the most recent government recommendations, pre-menopausal women may need extra iron since they often don't get what they need from food, particularly if they are vegetarians. But some research suggests that too much iron may not be good for health. Men, and women after menopause, should choose supplements without iron, or with no more than 10 milligrams.

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If you know you need calcium, don't count on a multiple vitamin-mineral supplement to give it to you. Most contain only 100 to 200 mg, equal to just two to five ounces of milk. For extra calcium, look at calcium-fortified juice, cereal, or other foods, or a separate calcium supplement.

Don't buy what you don't need. Some "stress" or "mega" vitamins supply well beyond 100 percent of daily value for many B vitamins. Most people get what they need of these vitamins anyway, and there is no evidence that extra amounts provide any additional benefits. Some supplements supply large amounts of minerals that either aren't necessarily needed by humans at all or do not appear to be lacking in anyone's diet. Don't pay extra for minerals like molybdenum, boron, nickel, silicon and vanadium.

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Some high-priced supplements contain an assortment of other added ingredients, like dehydrated broccoli or spinach, oat bran, or ginko biloba (an herbal product that some research links with maintaining mental function). However nutritious or helpful these foods or substances may be, the amounts in multi-vitamin pills are too small to matter.

Finally, don't overestimate what a supplement can do. Researchers emphasize that the benefits of eating fruits and vegetables are due to much more than vitamins and minerals. They contain different types of health-promoting dietary fiber and a wide range of natural phytochemicals that promote good health in a variety of ways that supplements just can't duplicate. That's why the AICR emphasizes that supplements can't substitute for the fruits and vegetables that should be the major part of our diet. Five to ten servings daily can make a major difference in better overall health as well as lowered risk of cancer and other chronic diseases.

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