Black women are known to have higher bone mineral density, associated with stronger bones, than white women. New findings suggest that one reason for this may be due to the slower rate of bone loss among elderly black women.

A team of researchers studied 6,007 Caucasian women and 482 African-American women, aged 65 to 94 years, and found that the rate of bone density loss was roughly two times slower in the black women than among their white counterparts.

“This observation is consistent with the lower rate of fracture observed in African-American women,” study author Dr. Jane A. Cauley, of the University of Pittsburgh, and her colleagues write in this month’s issue of the Journal of the American Geriatrics Society.

Previous research shows that African-American women have a 50-percent lower risk of experiencing hip fracture and other fractures. The reason for black women’s higher bone mineral density is unclear, yet, such differences have been found to be evident even during the childhood years.

Studies have shown that the higher bone mineral density found among African-American children, in comparison to white children, seems to persist into old age, in some cases, even among women in their 80s or older.

In the current study, Cauley and her colleagues investigated rates of bone loss, which might explain the differences in bone mineral density among black and white women. To determine changes in bone mineral density, they evaluated the women’s hip bones - the site best known to predict hip fracture - at the start of the study and again a few years later.

As mentioned, they found that the Caucasian women lost bone density at twice the rate of the African-American women. Each year white women lost an average of 0.58 percent bone mineral density of the total hip, compared with a 0.31-percent loss in black women, the report indicates.

Based on this finding, Cauley and her team estimated that the white women would lose an average 3 percent of hip bone mineral density over a five-year period, while black women would lose 1.5 percent.

In other findings, older women who were 75 years of age or older experienced a higher rate of bone mineral density loss than did younger women.

“Rates of bone loss increase in both groups,” Cauley told Reuters Health. This finding was particularly evident among African-American women, which suggests that “very old African-American women may start to have an increasing rate of fracture,” Cauley said.

Women who used hormone therapy had a slower rate of bone loss than non-users, but the rate of bone loss was slower among African-American hormone therapy users than among their Caucasian counterparts.

The reason for the slower bone mineral density loss among African-American women is unknown. Cauley intends to study the potential influence of vitamin D, as well as sex and growth hormones.

While the current findings point to the increased risk of bone thinning among white women, Cauley maintains that it is important for all women to be aware of the factors that increase their risk of bone fracture and the brittle-bone disease, osteoporosis.

African-American women are often overlooked for these conditions since they are known to be at lower risk, but “there are still African-American women who have osteoporosis,” Cauley said.

All elderly women who are thin, experienced early menopause or have other risk factors should get a bone density test, Cauley advised.

In 2002, the US Preventive Services Task Force issued recommendations advising women age 65 or older to undergo routine screening for osteoporosis. Their recommendations, published in the Annals of Internal Medicine, were based on increasing evidence suggesting that a woman’s risk of osteoporosis increases with increasing age, and that bone density tests can determine her risk of fracture in the short term.

SOURCE: Journal of the American Geriatrics Society, February 2005.