Positive association between serum 25-hydroxyvitamin D level and bone density in osteoarthritis

OBJECTIVE: To describe the association between serum 25-hydroxyvitamin D (25OH]D) level and bone mineral density (BMD) in persons with primary knee osteoarthritis (OA). METHODS: We conducted a population-based survey of the Framingham Study. A total of 228 subjects with primary radiographic knee OA were identified. For vitamin D status, 25(OH)D levels < or =15 ng/ml were classified as vitamin D deficient, 25(OH)D levels 16-32 ng/ml were classified as hypovitaminosis D, and 25(OH)D levels >32 ng/ml were classified as vitamin D replete. We compared average BMD between categories of 25(OH)D levels in subjects with OA using a linear regression model while adjusting for sex, age, body mass index (BMI), knee pain, physical activity, cohort, and disease severity. RESULTS: Mean age was 74.4 years and 36% were men. Of 228 individuals, 15% were vitamin D deficient, 51% had hypovitaminosis D, and 34% were vitamin D replete. Compared with subjects with vitamin D deficiency, those with hypovitaminosis D had a 7.3% higher BMD (adjusted percent difference; P = 0.02) and vitamin D replete subjects had an 8.5% higher BMD (adjusted percent difference; P = 0.02; test for trend across categories: P = 0.04). CONCLUSION: We observed a significant positive association between serum 25(OH)D and BMD in individuals with primary knee OA, independent of sex, age, BMI, knee pain, physical activity, and disease severity. Given the high prevalence of low 25(OH)D status in persons with knee OA and the positive association between 25(OH)D and BMD, vitamin D supplementation may enhance BMD in individuals with OA.