Expert Opinions

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I take calcium for bone strength but am confused about which type to buy. Is there a difference between calcium citrate and carbonate?

S.E., Irvine, CA

Yes, there is a difference, according to studies at the University of Texas Southwestern Medical Center at Dallas. Of the two types, the body absorbs much more calcium from the citrate form. In one study, the researchers examined blood samples from 18 postmenopausal women. They found that when the women took calcium citrate supplements, calcium levels were 2.5 times higher than when the women took the same amount of calcium from carbonate supplements.

"Our results show that calcium carbonate is not nearly as well absorbed as calcium citrate," states Dr. Howard Heller, coauthor of one of the studies. "We were surprised at the difference."

Calcium is important for preventing osteoporosis, or brittle bone disease. Most people normally get only about 500 mg of the mineral in their daily diet; at least 1,200 mg a day is recommended. Different types of calcium supplements contain different amounts of the mineral, and you may be able to get enough extra calcium with calcium carbonate or another form of the supplement. But calcium citrate may be an especially good choice, particularly for people over age 65, who lack sufficient stomach acid to absorb calcium carbonate. To enhance absorption, don't consume more than 600 mg at any one time.

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