Low selenium levels associated with knee OA risk, severity

Each 0.1 ppm increase in bodily selenium levels may decrease the risk of knee osteoarthritis by up to 20%.

Patients who do not receive adequate amounts of selenium in their diets have a higher risk of developing knee osteoarthritis, according to a study by North Carolina researchers.

Joanne M. Jordan, MD, MPH, and colleagues at the University of North Carolina (UNC) at Chapel Hill’s Thurston Arthritis Center found that each additional 0.1 ppm increase in bodily selenium levels decreased the risk of knee osteoarthritis (OA) 15% to 20%.

Additionally, below normal selenium levels increased the risk of developing OA in one or both knees, with disease severity related to the extent of the deficiency.

“We are excited about these findings because no one had ever measured body selenium in this way in relationship to osteoarthritis,” Jordan said in a press release announcing the study results. “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.”

Jordan is an associate professor of medicine and orthopedics at the UNC School of Medicine. She is also principal investigator of the Johnston County Osteoarthritis Project (JCOP), a federally supported OA study that has been ongoing for 15 years and has involved about 4400 patients.

The new study involved data for 940 patients enrolled in the JCOP. These patients had a mean age of 59.8 years; 39.8% were Black and 33% were men.

The researchers reviewed radiographs for evidence of knee OA. They then compared the extent of knee OA with patients’ bodily selenium levels, which were determined by Instrumental Neutron Activation Analysis of toenail clippings.

Overall, selenium levels averaged 0.75 ppm. However, patients with knee OA, bilateral knee OA and severe OA all had significantly lower mean selenium levels (P<.05).

The researchers also noted significant differences in mean selenium levels between races and genders. Black patients had a mean selenium level of 0.71 ppm, significantly lower than the mean level of 0.78 ppm seen for white patients (P<.0001). Men had a mean selenium level of 0.73 ppm compared to the significantly higher mean level of 0.76 ppm for women (P<.0001), according to the study.

“We found that when we divided the participants into three groups, those with the highest selenium levels faced a 40% lower risk of knee OA than those in the lowest-selenium group,” Jordan said in the press release. “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.”

Compared to patients in the lowest selenium tertile, patients in the highest selenium tertile had an adjusted odds ratio of 0.62 (95% CI, 0.37 to 1.02) for developing knee OA, an odds ration of 0.54 (0.31 to 0.97) for bilateral knee OA and of 0.56 (0.34 to 0.94) for severe OA, according to the study.

The results suggest a clear relationship between selenium and OA, Jordan said. “The next step will be in the laboratory to see how selenium affects cartilage. 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,” she said.

Most people in the U.S. get enough selenium in their diets if those diets are varied and include foods from different regions, Jordan added.

The study was supported by the Centers for Disease Control and Prevention and by the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health.

For more information:
Jordan JM, Fang F, Arab L, et al. Low selenium levels are associated with increased risk for osteoarthritis of the knee.#1189. Presented at the American College of Rheumatology 2005 Annual Scientific Meeting. Nov. 13-17, 2005. San Diego.