medwireNews: Vitamin D intake is inversely associated with cartilage degeneration among patients with osteoarthritis (OA), and supplementation may have a protective effect, suggests an analysis of data from the Osteoarthritis Initiative.
In the cross-sectional part of their study, Gabby Joseph (University of California, San Francisco, USA) and colleagues found a significant inverse association between self-reported dietary vitamin D intake and cartilage degeneration among 1785 patients with a Kellgren–Lawrence score of 3 or lower in the right knee.
Specifically, higher vitamin D intake was significantly associated with a reduction in cartilage WORMS score – a modified semi-quantitative whole-organ magnetic resonance imaging score, where lower scores indicate less degeneration – with an estimated drop of 0.24 points for each standard deviation increase in vitamin D.
Moreover, daily vitamin D supplementation was significantly associated with lower cartilage WORMS score in the medial femur in the cross-sectional analysis.
The researchers also demonstrated a longitudinal association between vitamin D supplementation and reduced joint degeneration over 4 years of follow-up among individuals who took supplements consistently. This association was dose-dependent, with 300 IU taken at least 4–6 days per week being the smallest dose and lowest frequency to show a significant inverse association with WORMS progression.
Joseph and team say that taking at least 400 IU of vitamin D on at least 1–3 days per week was associated with a significantly reduced risk for cartilage, meniscus, and bone marrow WORMS score worsening over 4 years, while taking 400 IU on at least 4–6 days per week was associated with a significantly reduced odds of joint structure degeneration.
Together, these findings “suggest that vitamin D intake is associated with less joint structure degeneration,” write the study authors in Arthritis Care & Research.
Discussing the possible mechanisms behind this association, they speculate that “vitamin D deficiency may adversely impact the pathogenesis of cartilage degeneration in OA, both directly through its impact on [extracellular matrix] activity and indirectly through its negative effects on bone metabolism.”
Joseph and colleagues also found a significant inverse association between vitamin C intake and joint degeneration in the cross-sectional analysis, but there were no significant associations in the longitudinal analysis.
They say that “previous studies have published varying results on the impact of vitamin C on the arthritic joint with some showing benefits, others showing no effects, and others reporting that high levels are associated [with] worsening of knee OA.”
The researchers note that their study was limited by its observational design and self-reported vitamin intake.
“A randomized controlled design would be better-suited to account for confounding and other factors; thus, the presented results should be interpreted with caution,” they conclude.
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