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

Objective: Knee pain from osteoarthritis is frequent in the adult population. Prior trials have had conflicting results concerning the therapeutic effects of vitamin D on knee pain, and few trials have investigated marine Omega-3 fatty acids (n-3 FA).

Methods: In the double-blind, placebo-controlled Vitamin D and Omega-3 Trial (VITAL), 25,871 US adults were randomized in a 2-by-2 factorial design to receive vitamin D or 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 using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) (graded on a 0-100 scale, where 100 indicates worst symptoms). Repeated measures modeling was used to test the effect of randomized treatment on WOMAC pain scores over follow-up after adjustment for age and sex. Analyses were repeated for WOMAC function and stiffness.

Results: This study included 1,398 participants who returned at least one knee pain questionnaire. The mean age was 67.7 years, 66% were women, and the mean ± SD WOMAC pain score was 37 ± 19. The mean ± SD follow-up time was 5.3 ± 0.7 years. WOMAC pain did not differ between the active vitamin D group and the vitamin D placebo group or between the active n-3 FA group and the n-3 FA placebo group at any time point during follow-up. Linear time-by-treatment interactions were not 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: Our findings indicate that vitamin D and n-3 FA supplementation for a mean of 5.3 years does not reduce knee pain or improve function or stiffness in a large sample of US adults with chronic knee pain.