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Taking Extra Calcium May Require Added Zinc

By Judy McBride
January 20, 1998

Consuming extra calcium from dairy products or supplements could put older women at risk of low zinc--unless they get extra zinc, too. That's the word from two studies at the USDA Jean Mayer Human Nutrition Research Center on Aging at Tufts, Boston. The center is funded by USDA's Agricultural Research Service.

Zinc's many functions include helping us maintain a healthy immune system, skin and appetite.

Calcium supplement sales have soared with the growing awareness that high intakes of this mineral help prevent osteoporosis. Some studies have found that extra calcium blocks zinc absorption; others haven't.

Richard J. Wood and Jia Ju Zheng looked for a zinc-calcium interaction in elderly women because, as a group, they tend to have low zinc intakes. About half of U.S. women consume less than two-thirds the Recommended Dietary Allowance of 12 mg, according to survey data. And the amount of zinc people absorb from their meals decreases with age.

In one of the new studies, 18 relatively healthy women past menopause increased calcium intake to 1,360 milligrams daily--a little higher than the 1,200 mg now recommended for people over age 50. Their zinc absorption dropped by an average of about 2 mg, as did zinc balance. This happened regardless of whether they got the extra calcium from milk or from a calcium phosphate supplement. The study lasted 36 days.

In a second study, zinc absorption dropped by half when a group of 10 men and women took a calcium supplement with a single test meal. But adding nearly 8 mg of zinc to the calcium supplement offset this effect.

While the data are too preliminary to recommend that women taking extra calcium also increase their zinc intake, they point in that direction. The richest dietary sources of zinc are oysters, liver and beef, followed by whole wheat products, nuts, popcorn, cheddar cheese, poultry, lamb and pork.

Scientific contact: Richard J. Wood, Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts, Boston, Mass., phone (617) 556-3192, fax (617) 556-3344, wood_mb@hnrc.tufts.edu.