University of North Carolina at Chapel Hill Thurston Arthritis Center medical scientists and colleagues conducted the research. It focused on the knees of 940 participants enrolled in the Johnston County (N.C.) Osteoarthritis Project, a continuing, federally supported investigation of osteoarthritis that began 15 years ago and is headquartered at UNC.
Scientists found that for every additional tenth of a part per million of selenium in volunteers’ bodies, there was a 15 percent to 20 percent decrease in their risk of knee osteoarthritis. Those who had less of the trace mineral than normal in their systems faced a higher risk of the degenerative condition in one and both knees. The severity of their arthritis was related to how low their selenium levels were.
"We are very excited about these findings because no one had ever measured body selenium in this way in relationship to osteoarthritis," said study leader Dr. Joanne Jordan of UNC. "Our results suggest that we might be able to prevent or delay osteoarthritis of the knees and possibly other joints in some people if they are not getting enough selenium. That’s important because the condition, which makes walking painful, is the leading cause of activity limitation among adults in developed countries."
Jordan is associate professor of medicine and orthopaedics at the UNC School of Medicine. Also associate director of the school’s Thurston Arthritis Research Center, she is principal investigator of the long-term Johnston County Osteoarthritis Project. That investigation is the largest and longest of its kind ever done and has involved some 4,400 volunteers, both blacks and whites, whose experiences with arthritis doctors follow and analyze.
Jordan and colleagues will present results of their study in San Diego Tuesday (Nov. 15) at the annual meeting of the American College of Rheumatology. Co-authors are UNC statistician Fang Fang; Dr. Lenore Arab of the University of California at Los Angeles; Dr. Steven J. Morris of the University of Missouri in Columbia; Dr. Jordan Renner, professor of radiology and allied health sciences at UNC; Dr. Charles G. Helmick of the Centers for Disease Control and Prevention (CDC) in Atlanta; and Dr. Marc C. Hochberg, professor of medicine at the University of Maryland.
The team got interested in the possibility that selenium might play a role in preventing osteoarthritis in part because in severely selenium-deficient areas of China, people frequently develop Kashin-Beck disease, which cause joint problems relatively early in life.
The U.S. study involved comparing the extent of knee osteoarthritis in each subject as shown on carefully examined X-rays with how much selenium was in their systems. At the University of Missouri, Morris determined the latter from toenail clippings taken during physical examinations in North Carolina. He employed a complicated nuclear technique known as Instrumental Neutron Activation Analysis.
"We found that when we divided the participants into three groups, those with the highest selenium levels faced a 40 percent lower risk of knee osteoarthritis than those in the lowest-selenium group," Jordan said. "Those in the highest selenium group had only about half the chance of severe osteoarthritis or disease in both knees. Some of the findings were even stronger in African-Americans and women."
The bottom line was that there appears to be a clear relationship between selenium and osteoarthritis, she said.
"The next step will be in the laboratory to see how selenium affects cartilage," Jordan said. "It might act as a protective antioxidant. Later, we’ll want to expand the study with larger samples and see whether selenium supplementation reduces pain or other symptoms."
Most people get enough selenium in their diets in the United States if those diets are varied and include foods that come from different regions, she said.
"If you were just growing most of your own food in soil that did not have much selenium and not eating vegetables and meat from elsewhere, you could potentially get in trouble with selenium deficiency," Jordan said.
Osteoarthritis, the most common form of arthritis, afflicts almost a million North Carolinians and more than 21 million people nationally, including many adults over age 65, the physician said. Some estimates suggest that as many as 70 million Americans will suffer from some form of arthritis within the next 20 years as baby boomers age.
Support for the research came from the CDC and the National Institute of Arthritis and Musculoskeletal and Skin Diseases.