CHAPEL HILL -- Older black men in the United States are about 33 percent more likely than white men here to suffer hip osteoarthritis, a new University of North Carolina at Chapel Hill study shows. Weight differences account for comparable disparities in the degenerative condition in women.
"We also found about the same proportion of African-American men having knee osteoarthritis as white men, but blacks were 65 percent more likely to have it in both knees and faced almost three times the risk of more severe knee osteoarthritis," said Dr. Joanne Jordan, research associate professor of medicine at the UNC-CH School of Medicine. "We're not sure why they get it worse. It might have something to do with physical demands of what they did at work, but none of the things we looked at seemed to explain the differences."
Black women were about twice as likely as white women to develop the condition, to get it in both knees and to experience greater severity, the study showed. Those differences, however, appeared to result from black women being heavier for their height than white women, said scientists, who controlled for obesity, age and education.
The study, being presented at an American College of Rheumatology meeting in Philadelphia this week, involved 3,145 randomly selected people participating in the Johnston County (N.C.) Osteoarthritis Project, a U.S. government-sponsored study that for the first time includes many black subjects. Most investigators consider the research to be the most definitive study ever done on racial differences in osteoarthritis.
Jordan is a member of the Thurston Arthritis Research Center at UNC-CH. Others involved in the study were Dr. Jordan Renner, associate professor of radiology, and Anca Dragomir and Gheorghe Luta, doctoral students in epidemiology and biostatistics, both at the UNC-CH School of Public Health.
A third of study participants, all over age 45, were black, and almost two-thirds were women. UNC-CH researchers found no differences in hip osteoarthritis in women of different races.
From earlier studies in Africa and the Caribbean, researchers expected to find little hip osteoarthritis among U.S. blacks, and so the new results were a surprise, Jordan said. Differences may result from diet, bone density disparities, genetic mixing or differing work experiences. Or they may result from some combination of the various factors.
"This study is important because it shows, really for the first time, that African-Americans have more severe knee osteoarthritis than Caucasians do in the United States, and that most of this, in women, is associated with greater body mass index," the physician said.
One take-home message is that people in general, and black women in particular, need to control their weight better, she said. Effective weight control would go a long way toward minimizing disabilities later in life.
"People can reduce the chance of developing knee and hip osteoarthritis or reduce their severity by losing weight and avoiding activities that put heavy physical stress on joints," Jordan said. "Evidence suggests it's also important to keep thigh and other leg muscles strong through non-stressful exercises."
The Centers for Disease Control and Prevention and the National Institute of Arthritis, Musculoskeletal and Skin Diseases support the continuing research.
The number of Americans suffering from osteoarthritis is expected to grow from 40 million people to 60 million by 2020, Jordan said.
Note: Jordan can be reached at the American College of Rheumatology meeting at the Philadelphia Marriott at (215) 625-2900. She will check for voice messages periodically and respond promptly. After the meeting, she can be reached at her UNC-CH office at (919) 966-0559.
Contact: David Williamson, (919) 962-8596.