HOW TO READ A MULTIVITAMIN LABEL

This made-up multivitamin label shows how much of each vitamin and mineral we need to get every day (from foods plus supplement according to the National Academy of Sciences' Institute of Medicine (IOM). The IOM's recommendations vary slightly by age and gender. In most cases, we picked the highest level for adults, excluding pregnant and breastfeeding women. The label also lists the Daily Value (DV) for each nutrient. The DVs, which haven't been updated in decades, are still used on multivitamin labels.

VITAMIN A (retinol). The Daily Value (5,000 IU, or International Units) is outdated. You need only 3,000 IU a day of vitamin A. Too much retinol (typically listed on labels as vitamin A palmitate or vitamin A acetate) may increase the risk of hip fractures, liver abnormalities, and birth defects. Beta-carotene, which the body converts to vitamin A, doesn't cause those problems, but very high doses (33,000 to 50,000 IU a day) may increase the risk of lung cancer in smokers. Our advice: Don't get more than 4,000 IU of retinol or 5,000 IU of beta-carotene from your multi (less retinol would be even better). Instead, load up on beta-carotene-rich fruits and vegetables like carrots, cantaloupe, sweet potatoes, and broccoli, which may help prevent some cancers.

VITAMIN D. It helps you absorb calcium and may reduce the risk of cancer, diabetes, and falls. Many people get too little vitamin D from sunshine (especially in the winter) or from their food. The Institute of Medicine recommends 200 IU a day for adults 50 and under, 400 IU for people 51 to 70, and 600 IU for anyone over 70. Some vitamin D experts say that everyone should get at least 1,000 IU a day. (We agree.) Those amounts include what you get from the sun, from salmon and other fatty fish, and from fortified foods like milk, breakfast cereals, and some brands of yogurt, margarine, and orange juice. They also include the vitamin D that's added to many calcium supplements. Most multivitamins have 400 IU of vitamin D (the DV).

THIAMIN (B-1), RIBOFLAVIN (B-2), NIACIN (B-3), B-6. The higher-than-DV levels in many multivitamins are harmless. Two exceptions: More than 100 mg a day of vitamin B-6 can cause (reversible) neurological damage. And as little as 50 mg a day of niacin can cause flushing. Super-high doses of niacin (3,000 mg a day or more) may cause liver damage, though you won't find that much in a multivitamin.

VITAMIN B-12. Most multivitamins have at least 6 mcg (the DV). That's more than the 2.4 mcg the Institute of Medicine recommends for adults, but it's perfectly safe. (So are the higher doses--600 to 800 mcg--that are found in a few multivitamins.) Ten to 30 percent of older people are unable to absorb the B-12 that's found naturally in food. So if you're over 50, get at least some of your B-12 in the form that's added to supplements and fortified foods. A B-12 deficiency can cause irreversible nerve damage and may masquerade as Alzheimer's disease.

IRON. Many people, especially premenopausal women, are deficient. But taking too much can cause constipation or iron overload if you're susceptible. Men and postmenopausal women should look for a multivitamin with no more than 10 mg of iron or should take a multi for premenopausal women every other day. The DV (18 mg) is fine for premenopausal women.

MAGNESIUM. Americans get too little from their food (among the best sources: whole grains and beans). A deficiency may increase the risk of diabetes and colon cancer. Look for a multi with at least 100 mg, just for insurance. The Institute of Medicine recommends 320 mg a day for women and 420 mg for men. More than 350 mg a day from a supplement may cause diarrhea.

SELENIUM. Many multis have less than the DV (70 mcg) or the Institute of Medicine's recommended level (55 mcg). A large study is under way to see if high doses (200 mcg a day) can lower the risk of prostate cancer. But a few studies have suggested that taking 200 mcg a day may raise the risk of skin cancer and diabetes, so it's safest to take no more than about 100 mcg a day.

IODINE, MANGANESE, MOLYBDENUM, CHLORIDE, BORON. Ignore. There's no evidence that people need more than what they get from their food.

DAILY VALUE (DV). The Daily Value for each vitamin or mineral is the Food and Drug Administration's advice on how much to shoot for each day (from food and supplements combined). In some cases, the numbers date from 1968 and don't reflect the latest research.

VITAMIN C. The DV (60 mg) is lower than the Institute of Medicine's recommendations (75 mg a day for women and 90 mg a day for men). Roughly 250 to 500 mg saturates the body's tissues, so more than that is probably excreted in the urine. Taking more than 1,000 mg of vitamin C at one time in a supplement may cause diarrhea.

VITAMIN E. Doses of 30 to 800 IU a day haven't protected against heart disease or stroke, and 400 IU a day or more may slightly raise the risk of dying. Studies are under way to see if 400 IU a day prevents prostate cancer. To play it safe, stick to no more than 100 IU.

VITAMIN K. The Institute of Medicine recommends 120 mcg a day, yet most multivitamins have much less than the DV (80 mcg). In recent studies, taking extra vitamin K didn't strengthen bones, as earlier studies had suggested. You can get K from leafy greens, some calcium supplements, and vitamin K supplements. Vitamin K can interfere with blood-thinning drugs like Coumadin, so people who take them should check with their doctor before taking a multi with vitamin K.

FOLIC ACID. If you could become pregnant, look for a multi with the DV (400 mcg) to reduce the risk of birth defects. Others should probably take less until studies clarify whether high intakes (roughly 1,000 mcg a day or more from supplements and foods combined) raise the risk of cancer. Since most multis have 400 mcg, one option is to take your "daily" multi every other day (see p. 5).

BIOTIN, PANTOTHENIC ACID. Ignore. You'd have to eat a bizarre diet to run short.

CALCIUM. Calcium may help prevent colon cancer and (with vitamin D) may reduce the risk of osteoporosis. Shoot for 1,000 mg a day (if you're 50 or younger) or 1,200 mg (if you're over 50). But men should get no more than around 200 mg from their multi, since 1,500 mg a day or more may raise prostate cancer risk.

PHOSPHORUS. Unnecessary to take in a multi. Too much may impair calcium absorption, and we already get more than we need from our food.

ZINC, COPPER. Look for 8 mg (women) or 11 mg (men) of zinc and 0.9 mg of copper. There's no harm in taking a multivitamin with the DVs (15 mg for zinc and 2 mg for copper), but don't take more than 23 mg of zinc. Getting more than 40 mg a day (from pills and foods like meat, poultry, beans, nuts, dairy foods, and fortified cereals) may make your body lose copper. And in one study, men who took more than 100 mg of zinc a day for at least 10 years were more than twice as likely to be diagnosed with advanced prostate cancer as men who took none.

CHROMIUM. The Institute of Medicine recommends only 20 to 25 mcg a day (women) or 30 to 35 mcg a day (men). Many brands have closer to 120 mcg (the DV), which is safe.

POTASSIUM. Ignore. The amounts in multivitamins are low. And while the potassium chloride that's used in supplements may lower blood pressure and the risk of stroke, it won't help prevent kidney stones and bone loss like the potassium citrate that's found in fruits and vegetables.

NICKEL, SILICON, TIN, VANADIUM. Ignore. It's not clear that they're needed.

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