Black women are less likely to suffer fractures from osteoporosis than white women with the same bone density measurements.

A multi-center study led by epidemiologist Jane Cauley of the University of Pittsburgh Graduate School of Public Health showed also that for black women, just as for white women, bones are more likely to break as their density decreases.

"It's well established that bone density measurements predict fractures in older white women," Cauley said. "But this has never really been shown in women of other races."

The findings, published today in the Journal of the American Medical Association, raise questions whether a diagnosis of osteoporosis should be based on different bone densities for women of different races and ethnicities.

At the start of the study, bone density of the hip and upper femur, or thigh bone, was measured in more than 600 black and 9,700 white postmenopausal women from the Monongahela Valley, Baltimore, Minneapolis and Portland, Ore.

During the next six years of monitoring, 58 black women sustained a total of 61 osteoporotic fractures, while 1,606 white women sustained 1,712.

The researchers noted that the black women had a 9 percent higher hip density and 15 percent higher femur density than their white counterparts, and also were older, heavier and had a lower intake of dietary calcium.

But at every bone density level, fracture rates were 30 to 40 percent lower in the black women compared to the white women, Cauley said. Differences in genes, hormone levels, bone metabolism or other factors could be playing a role.

Even though black women are less likely to sustain the injury, "they have an increased risk of dying following a hip fracture compared to white women," Cauley pointed out. "So the public health impact [of osteoporosis screening] may be greater in these women."

She added that the findings suggest different races and ethnicities might require different bone density thresholds for the diagnosis of osteoporosis.

But much more has to be learned about racial and ethnic variation and its interplay with other fracture risk factors before treatment models can be built around it, said Dr. Louise Acheson, of Case Western Reserve University, in another article in the journal.

"Data showing higher fracture risk with low [bone denisty] in all ethnic groups is an important step," she said.