African-American women have a lower risk of fracture than their Caucasian counterparts regardless of bone mineral density (BMD), according to a new study that calls for race-specific norms of BMD to define osteoporosis. The new findings appear in the May 4 issue of the Journal of the American Medical Association.1
The study detected 61 fractures among 58 African-American women, while 1,606 Caucasian women had a total of 1,712 fractures during the same period. Exactly why such a discrepancy exists is unclear, but "genetic factors and bone-related factors like turnover and architecture of bone play a role," lead researcher Jane A. Cauley, Dr.P.H, an epidemiologist at the University of Pittsburgh in Pennsylvania, tells CIAOMed. "We are also interested in looking at whether differences in levels of sex hormones in blood and in cytokines contribute to the differences between the races."
At the beginning of the study, African-American women had a 9% higher total hip BMD and a 15% higher femoral neck BMD than did Caucasian women, according to data from the Study of Osteoporotic Fractures. The association between BMD and fracture was weakened when adjusted for body weight and other risk factors, especially among African-American women. The absolute incidence of fracture across the pooled BMD distribution was 30% to 40% lower among black women at every BMD tertile.
Race-specific BMD databases warranted
"Within the black population, we can still identify women at risk of fractures," says Dr. Cauley. "In a woman who is older and has risk factors of osteoporosis, it is still prudent to get a bone density measurement, but [the results] should be compared to other black women - not a white reference database," she says.
In 2001, a panel convened by the International Society for Clinical Densitometry concluded that there was not enough data to recommend using race-specific norms of BMD to define osteoporosis for non-Caucasians.
However, given that the current data suggest African-American women have a lower fracture risk than do their Caucasian counterparts, the authors suggest that race-specific normative databases may now be appropriate for the densitometric definition of osteoporosis.
The prospective cohort study culled data on nonspinal fractures in older women who took part of the Study of Osteoporotic Fractures. Data were collected between 1986-1990 from 7,334 Caucasian women aged 67-99 years, and between 1996-1998 from 636 African-American women aged 65-94 years, with an average 6.1 years of follow-up.
Consequences of fractures may vary among races
"Even though black women have a lower risk of fracture, the consequences may be greater," she says. In particular, "mortality after hip fracture is greater in black women, and it could be due to the fact that they [are] older or sicker, or it could start a downward spiral because of other co-morbid conditions," Dr. Cauley says.
So far, there is no evidence to indicate that treatment efficacy differs between races, according to Dr. Cauley. "There is no evidence that they would work differently, but we primarily only have data on alendronate and hormone replacement therapy," she says.
Other risk factors in African-American women?
"Afro-American women who fracture do so at a higher BMD than Caucasian women, and it just means that the risk of fractures in Afro-American women is not as highly associated with low BMD to the same degree as Caucasian women," says CIAOMed advisory board member Nancy Lane, MD, associate professor of medicine at the University of California, San Francisco. "Basically, other factors independent of BMD are associated with the risk of fractures in elderly Afro-American women." Exactly what other factors are at play is not clear, she says, adding that it is "probably some localized changes within the bone that at present cannot be measured."
In an accompanying editorial2, Louise S. Acheson, MD, MS, associate professor of family medicine at Case Western Reserve University in Cleveland, Ohio, notes that race is not a precise enough category to gauge fracture risk. "There must be other factors related to fractures besides BMD that may be able to be measured clinically," she tells CIAOMed. "If we could measure and use this information clinically to individualize therapy, it may be a more precise way to do things than to recommend different treatments based on race."
Specifically, she writes, "If-besides BMD-bone geometry, body composition, bone metabolism, physical capacity, fall risk, and eventually genotype are race-related variables determining fracture risk, measurements related to these factors could be evaluated clinically."
In the editorial, she notes that race "is a nonbiological category, an extremely crude surrogate for biological, environmental, cultural, and behavioral differences among individuals and human populations."
References:
- Cauley JA, Lui L-Y, Ensrud KE, et al. Bone mineral density and the risk of incident nonspinal fractures in black and white women. JAMA 2005;293:2102-2108.
- Acheson LS. Bone density and the risk of fractures: should treatment thresholds vary by race? JAMA 2005;293:2151-2154.