Ethnic differences in arthritis due to obesity

NEW YORK (Reuters Health) - Older African-American, Native American and non-white Hispanic women are more likely to develop arthritis than their white counterparts, and the larger prevalence of obesity among these ethnic groups may help explain why, new research shows.

Among 146,494 women participating in the Women's Health Initiative -- an ongoing study of an ethnically diverse group of healthy postmenopausal women -- 44 percent had been diagnosed with osteoarthritis (degeneration of the joints), the most common form of arthritis.

These women were older and less active than their arthritis-free peers, and were also less educated, poorer, and heavier, Nicole C. Wright and colleagues from the University of Arizona in Tucson Wright report in the Journal of the American Geriatrics Society.

As expected, women in their 70s were at greater risk of osteoarthritis than women in their 50s, while the risk for women in their 60s fell in between.

Overall, the researchers found, osteoarthritis risk was slightly increased for Native American and African American women compared to non-Hispanic white women, while Asian women were at lower risk than whites.

Risk factors for osteoarthritis were more common among black, Native American and Hispanic women than whites; 57.9 percent of African Americans were obese, for example, compared to 51 percent of American Indian women, 41.9 percent of Hispanic women, and 32.9 percent of non-Hispanic whites.

Prevalence of physical inactivity followed the same pattern, with 30.1 percent of black women falling into the lowest activity group, compared to 19.5 percent of whites.

Osteoarthritis prevalence among the youngest women participating in the study also varied by ethnicity, with 39.3 percent of Hispanic women in their 50s reporting arthritis, 36.4 percent of Native Americans, 33.8 percent of black women, 25.8 percent of Asians and 22.6 percent of whites.

The researchers hypothesize that excess weight could contribute to arthritis in two ways: by increasing physical stress on joints, and also by increasing bone mineral density, which may increase bone stiffness and thus contribute to the breakdown of cartilage.

The findings, along with other studies showing that black and Hispanic women suffer more pain and disability from osteoarthritis than do whites, offer "strong evidence that body weight and BMI may be large contributing factor to the number and severity of osteoarthritis symptoms, further elaborating the importance of postmenopausal women, especially African-American, Hispanic, and American-Indian women, maintaining a healthy weight," Wright and her team wrote.

SOURCE: Journal of the American Geriatrics Society, 2008.