Spin the bottle: how to pick a multivitamin

Nutrition Action Healthletter, Jan-Feb, 2003 by Bonnie Liebman

Manufacturers have been skittish about adding much vitamin K because it can interfere with popular blood-thinning drugs like coumadin. But it's safe for others. In fact, recent studies suggest that people may need 150 to 250 mcg a day to prevent hip fractures.

Our Best Bites have at least 20 mcg of vitamin K. (Our chart lists vitamin K, so you can find brands that have more.) To make sure you're getting enough, load up on leafy greens like spinach, kale, broccoli, Brussels sprouts, and romaine lettuce (see July/August 2002, p. 13). Some calcium supplements also have vitamin K. (Viactiv, for example, has 40 mcg per chew.) If you're taking blood-thinners, talk to your doctor about how much vitamin K to get from your food and supplements.

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Get a minimum of minerals

Our Best Bites have less than 100 percent of the Daily Value for most minerals, but for different reasons:

* For chromium, copper, selenium, and zinc: We required less than the Daily Values because the latest recommendations are lower than the outdated DVs. The National Academy cut copper from 2 mg to 0.9 mg (900 mcg), selenium from 70 mcg to 55 mcg, and zinc from 15 mg to 11 mg (and to 8 mg for women). Chromium dropped from 120 mcg to a range of 20 mcg to 35 mcg, depending on your age and gender.

* For calcium and magnesium: Our Best Bites have less than the Daily Values because the recommended levels are too large to fit in a single pill. We set no minimum for calcium, because to get the recommended amount (1,000 mg to 1,200 mg a day), most people would probably need a separate supplement anyway. (You might be able to get a day's worth in a four-pills-or-more-a-day multi, but you'll probably pay more than you would by buying calcium and magnesium separately.)

We required at least 100 mg of magnesium, which can give you a boost towards the recommended levels for women (320 mg) or men (420 mg). You might not want those higher levels in your multi anyway. Getting more than 350 mg from a supplement or fortified food may cause diarrhea. Better to get more magnesium from whole-grain breads and cereals.

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Avoid excesses

Our Best Bites had no more than 4,000 IU of retinol (more may increase the risk of hip fractures in women), 15,000 IU of beta-carotene (more may increase the risk of lung cancer in smokers), 100 mg of vitamin B-6 (more may cause reversible nerve damage), 350 mg of magnesium (more may cause diarrhea), and 250 mg of phosphorus (we already get too much from our food).

For iron, there is no amount that's right for everyone. Our Best Bites for women have 18 mg, because women under 50 need that much to replace menstrual losses. But Best Bites for men and postmenopausal women have no more than nine milligrams of iron, to lower the risk of iron overload and possibly (the evidence is shaky) heart disease and cancer.

We set no limit on vitamin E for Best Bites. But in a new study, women with heart disease who were given 800 IU of vitamin E (and 1,000 mg of vitamin C) every day for three years were more likely to die than similar women who got a placebo (see page 12).