Women who get most of their daily calcium from food have healthier bones than women whose calcium comes supplements, even if the vitamins increase total calcium, researchers at Washington University said.

Researchers asked 183 postmenopausal women to detail their diets and calcium intake. They ended up in three groups -- those who got 70 percent of calcium from food, those who got 70 percent from supplements, and those who fell in the middle.

They tested the women's bone density and urinary markers of calcium.

The diet group had the lowest calcium intake at 830 milligrams a day. But they had higher bone densities than the supplement group, which took in an average of 1,030 milligrams a day.

Those who had a balance of dietary and supplemental calcium had the highest density and the highest intake, at nearly twice as much as the food and drink group.

The urinalysis indicated that those with more calcium from natural sources had more active estrogen, which controls bone density.

Lead author Dr. Reina Armamento-Villareal said the results may be because of how other nutriets affect the metabolism, or the different ways supplements are absorbed.

"Only about 35 percent of the calcium in most supplements ends up being absorbed by the body," Armamento-Villareal said.

Adequate calcium is considered important to prevent osteoporosis, which affects an estimated 8 million American women and 2 million American men.