May 3, 2005 -- Older black women may have a lower bone-fracture risk than their white peers, even when compared to those who have similar bone density measures.bone density measures.
"Black women have a lower fracture risk at every level of bone mineral density," write Jane Cauley, DrPH, and colleagues in the May 4 issue of The Journal of the American Medical Association.
Bone density and fracture risk are assessed by imaging called a bone mineral density test. The test identifies low bone mineral density, which indicates thin, fragile bones and an increased risk of fracture.thin, fragile bones and an increased risk of fracture.
Low bone mineral density was associated with increased risk of bone fractures in both black and white women, say the researchers. However, they say bone fracture rates were 30% to 40% lower for black women at every level of bone mineral density.
Race-specific databases may be appropriate for defining osteoporosis, write Cauley and colleagues, calling for more studies. A journal editorial agrees that more work is needed on the topic.
Men are also at risk for osteoporosis as they age. This study did not include any men.
Cauley's study included 7,334 white women aged 67-99 and 636 black women aged 65-94. Their height, weight, and hip bone density were measured.
Every four months for about six years, the women were contacted by letter or phone to ask if they'd had any bone fractures. The study did not include fractures of the spine or those sustained in a major trauma, such as a car crash. Reported fractures were confirmed by X-rays.
Women could report more than one fracture.
A total of 1,712 bone fractures were reported by 1,606 white women. There were 61 bone fractures among 58 black women.
Body weight, height, age, and other factors were also considered. For instance, the researchers noted if the women took calcium supplements, walked for exercise,walked for exercise, used hormones, and drank alcohol.
Those factors have been shown to affect bones. For instance, adequate calcium intake is believed to protect bones, while drinking too much alcohol may sap bone strength. Thin women are also at increased risk of osteoporosis, a condition that can run in families.
In Cauley's study, the black women were older and heavier than the white women. They were also less likely than whites to take calcium supplements, walk for exercise, or consume alcohol, say the researchers.
After taking into account a woman's age and low bone mineral density and other factors associated with increased fracture risk, black women were 48% less likely than white women to have bone fractures, says the study.
Groups With Higher Bone Risks
Looking just at the black women in the study, those who had a bone fracture tended to have a couple of things in common:
- Slightly older age
- Lower height, weight, and body mass index (BMI)Lower height, weight, and body mass index (BMI)
- Less likely to report walking as a form of exercise
- More likely to report osteoarthritis
- More likely to report falling two or more times in the past year
- More likely to say they needed to use their arms to stand up from a chair
Cauley notes that the small number of black women in the study could have affected the estimates. Because all of the participants were volunteers and could walk without assistance, they might be healthier than other women their age, she and her colleagues add.
Some studies have suggested that black women have slower rates of bone loss, possibly due to slower bone metabolism, say Cauley and colleagues, adding that other studies haven't come to that conclusion.
Race was reported by participants. Future studies might consider the race and ethnicity of participants' grandparents, as well as genetic and cultural factors, say Cauley and colleagues.
Editorial writer Louise Acheson, MD, MS, calls race a "nonbiological category." She says that the words "white" and "black" may be misleading because they can group together people with different ancestries, histories, and environmental exposures.
For instance, she says women from Somalia living in the U.S. have lower bone mineral density than U.S. black women, and white women in France have lower peak bone mass than U.S. white women.
"Scientists and clinicians will do best by avoiding race proxies for other biological, social, and cultural constructs," writes Acheson, who works in the family medicine research division of Case Western Reserve University.