The Effects of Vitamin D and Marine Omega-3 Fatty Acid Supplementation on Chronic Knee Pain in Older U.S. Adults: Results from a Randomized Trial.

OBJECTIVE Knee pain from osteoarthritis is frequent in the adult population. Prior trials have had conflicting results concerning vitamin D's therapeutic effects on knee pain and few trials have investigated marine omega-3 fatty acids (n-3 FA). METHODS The double-blind, placebo-controlled VITamin D and OmegA-3 TriaL (VITAL) randomized 25,871 U.S. adults in a two-by-two factorial design to vitamin D and n-3 FA. We identified a subgroup with chronic knee pain prior to randomization and assessed knee pain at baseline and annually during follow-up with the Western Ontario and McMaster Universities Arthritis Index (WOMAC; 0-100, 100 worst). Repeated measures modeling tested the effect of randomized treatment on WOMAC Pain over follow-up after adjustment for age and sex. Analyses were repeated for WOMAC Function and Stiffness. RESULTS We included 1,398 participants who returned at least one knee pain questionnaire. Mean age was 67.7 years, 66% were female, and mean WOMAC Pain was 37 (SD 19). Mean follow-up time was 5.3 years (SD 0.7). WOMAC Pain did not differ between vitamin D or n-3 FA and placebo at any time point during follow-up. Linear time by treatment interactions were not statistically significant for either treatment (vitamin D p= 0.41, n-3 FA p= 0.77). Vitamin D and n-3 FA supplementation did not significantly affect WOMAC Function or Stiffness scores over time. CONCLUSION Vitamin D and n-3 FA supplementation for a mean of 5.3 years did not reduce knee pain or improve function or stiffness in a large sample of U.S adults with chronic knee pain.