Women who want to keep their bones strong after menopause may be better off eating plenty of calcium-rich food than relying on supplements for their intake of the mineral, a new study shows.

Postmenopausal women who got their calcium mainly from diet or from diet and supplements had a greater average bone mineral density (BMD) than women who got most of their calcium from supplements, principal investigator Dr. Reina C. Armamento-Villareal of Washington University School of Medicine in St. Louis and her colleagues found.

"If you can get it from the diet that's the best source," Armamento-Villareal told Reuters Health.

In their report in the American Journal of Clinical Nutrition, she and her colleagues point out that calcium influences how the body metabolizes estrogen, a key bone-building hormone. To better understand the calcium-estrogen relationship, Armamento-Villareal and her team looked at how different forms of calcium affected BMD.

The researchers also looked at the ratio of active to inactive estrogen metabolites in the urine. Active estrogen metabolites have estrogen-like affects on the body, meaning they can help build bone, while inactive metabolites have no estrogenic effects.

The researchers looked at 168 healthy postmenopausal women. Thirty-three received most of their calcium from supplements, averaging about 1,030 mg daily; 70 didn't take supplements, and received a daily average of 830 mg of calcium; and 65 women received dietary and supplemental calcium, for a total daily average intake of 1,620 mg.

Women in the diet group and those in the diet plus supplement group had higher ratios of active to inactive estrogen metabolites in their urine compared with women in the supplement-only group, the researchers found.

The women in groups that did not receive supplements, even those in the diet-only group who took in less total calcium, also had higher BMD at several sites in the skeleton.

There are a number of mechanisms by which dietary calcium might build bones more efficiently than supplemental calcium, the researchers note. Calcium from dairy and other foods may be easier for the body to metabolize. It may also be, they add, that women who eat a calcium-rich diet may have been healthier eaters all their lives.

Nevertheless, Armamento-Villareal points out that, the total amount of calcium intake is still important, and women who can't stand eating dairy should be sure to get enough of the mineral by taking supplements.