Baseline 25-hydroxyvitamin D levels predict the effects of vitamin D supplementation on joint symptoms and cartilage loss in patients with knee osteoarthritis.

Objectives: To examine whether the baseline vitamin D level modifies the effects of vitamin D supplementation on knee symptoms and cartilage loss in patients with symptomatic knee OA.

Methods: This was a post hoc analysis for the VIDEO study, which was a large (n = 413), randomized, double-blind, placebo-controlled clinical trial in knee OA patients with 25-hydroxyvitamin D [25(OH)D levels ranging from 12.5 to 60 nmol/l]. Knee pain was assessed using the WOMAC pain scale. MRI scans of the knee were obtained. Cartilage volume, cartilage defects (0-4) and bone marrow lesions were measured or graded. Classification trees were applied to categorize the subgroups.

Results: A total of 413 participants (mean age 63.2 years; 50% women) were randomly assigned to vitamin D and placebo groups. A baseline 25(OH)D level of 43 nmol/l was found as the cut-off value. For the total WOMAC score, vitamin D supplementation decreased more than placebo in patients with 25(OH)D levels of 12.5-43 nmol/l (-256.41 vs -72.10, P = 0.0060) over 2 years but not in those with 25(OH)D levels of 43-60 nmol/l. Comparatively, vitamin D supplementation reduced the total cartilage volume loss (-0.21 vs -0.31, P = 0.0415) and total cartilage defects progression (0.26 vs 0.92, P = 0.0029) in patients with 25(OH)D levels of 43-60 nmol/l but not in those with 25(OH)D of 12.5-43 nmol/l.

Conclusion: Supplementation of vitamin D in patients with OA who have 25(OH)D levels ≤43 nmol/l could relieve pain and improve physical function, while in OA patients with 25(OH)D levels >43 nmol/l, supplementation may ameliorate cartilage lesions.

Trial registration: clinicaltrials.gov, NCT01176344; anzctr.org.au, ACTRN12610000495022.