RELATION OF DIETARY-INTAKE AND SERUM LEVELS OF VITAMIN-D TO PROGRESSION OF OSTEOARTHRITIS OF THE KNEE AMONG PARTICIPANTS IN THE FRAMINGHAM-STUDY

Background: Evidence suggests that pathophysiologic processes in bone are important determinants of outcome in osteoarthritis of the knee. L ow intake and low serum levels of vitamin D may compromise favorable r esponses of bone to osteoarthritis, predisposing patients to progressi on. Objective: To determine whether dietary intake and serum levels of vitamin D would predict the incidence and progression of osteoarthrit is of the knee in participants of the Framingham Study. Design: Prospe ctive observational study. Setting: The Framingham Study. Participants : Participants in the Framingham Heart Study who had knee radiography at examinations 18 (done between 1983 and 1985) and 22 (done between 1 992 and 1993) and received interim assessments of vitamin D intake and serum levels. Measurements: Intake of vitamin D and serum levels of 2 5-hydroxyvitamin D, calculated on the basis of dietary habits and supp lement use as reported on a questionnaire, were evaluated at examinati on 20 (1988 to 1989). Knee radiographs were given scores for global se verity of osteoarthritis, using a modification of the scale of Kellgre n and Lawrence (range, 0 to 4), and for the presence of osteophytes an d joint-space narrowing (range, 0 to 3). Covariates measured at examin ations 18 and 20 were age, sex, body mass index, weight change, injury , physical activity, health status, bone mineral density, and energy i ntake. Results: 556 participants (mean age at baseline +/- SD, 70.3 +/ - 4.5 years) had complete assessments. Incident osteoarthritis occurre d in 75 knees; progressive osteoarthritis occurred in 62 knees. Serum levels of vitamin D were modestly correlated with vitamin D intake (r = 0.24). Risk for progression increased threefold in participants in t he middle and lower tertiles for both vitamin D intake (odds ratio for the lower compared with the upper tertile, 4.0 [95% Cl, 1.4 to 11.6]) and serum levels of vitamin D (odds ratio for the lower compared with the upper tertilee, 2.9 [Cl, 1.0 to 8.2]). Low serum levels of vitami n D also predicted loss of cartilage, as assessed by loss of joint spa ce (odds ratio, 2.3 [Cl, 0.9 to 5.5]) and osteophyte growth (odds rati o, 3.1 [Cl, 1.3 to 7.5]). Incident osteoarthritis of the knee occurrin g after baseline was not consistently related to either intake or seru m levels of vitamin D. Conclusions: Low intake and low serum levels of vitamin D each appear to be associated with an increased risk for pro gression of osteoarthritis of the knee.