Women taking calcium supplements may be raising their risk

THE QUESTION Kidney stones, which have calcium as a major component, have become increasingly common among American women, by some reports afflicting nearly 40 percent more women in recent decades than in the 1970s. At the same time, older women are being urged to take calcium supplements, combined with Vitamin D for better absorption, to protect their bones. Might there be a link?

THIS STUDY analyzed data on 36,282 post-menopausal women who, at the start of the study, took in virtually the same amount of calcium daily (about 1,145 milligrams). They were randomly assigned to take supplements of calcium (500 milligrams) plus Vitamin D (200 international units) twice daily with meals or to take placebo pills for seven years. During that time, kidney stones developed in 830 of the women. The development of kidney stones was 17 percent more common among women taking the supplements than among those in the placebo group.

WHO MAY BE AFFECTED? Post-menopausal women, who are especially prone to loss of bone density and the occurrence of osteoporosis. Current guidelines call for women age 51 and older to take in 1,200 milligrams of calcium daily. This includes calcium from dietary sources, such as dairy products and leafy green vegetables, as well as supplements.

CAVEATS The development of kidney stones was recorded just once for each participant; recurrences were not noted, which might have affected the results. Some of the data came from the women’s answers on questionnaires. Some participants had had urinary tract stones in the past, but the study found no link to an increased risk.

FIND THIS STUDY July issue of the American Journal of Clinical Nutrition (

LEARN MORE ABOUT kidney stones at www.kidney.niddk.nih.

Linda Searing

The research described in Quick Study comes from credible, peer-reviewed journals. Nonetheless, conclusive evidence about a treatment's effectiveness is rarely found in a single study. Anyone considering changing or beginning treatment of any kind should consult with a physician.