Long-term effects of vitamin D supplementation and maintaining sufficient vitamin D on knee osteoarthritis over 5 years

OBJECTIVES: This study aimed to investigate the long-term effect of vitamin D supplementation compared to placebo over 5 years in participants with knee osteoarthritis (OA). We also aimed to describe the effect of maintaining sufficient serum vitamin D levels over five years in knee OA. METHODS: Participants (n = 173) from the Hobart centre of the Vitamin D Effects on Osteoarthritis (VIDEO) trial were extensively followed up 3 years after the cessation of 2-year investigational treatment. Participants were classified as maintaining sufficient vitamin D (n = 79) and not maintaining sufficient vitamin D (n = 61) groups. RESULTS: There was no significant difference in change in the knee symptoms, depression, and serum levels of IL6 and hs-CRP between both comparisons after 3 years of cessation of the clinical trial. However, among participants who reported no knee surgery (KS), there was a significant improvement in WOMAC function (β: − 83.7, 95% CI: − 167.3, 0) and depression scores (β: − 1.3, 95% CI: − 2.3, − 0.2) in vitamin D group compared to the placebo group. Similarly, those who maintained adequate vitamin D levels over 5 years had significantly less WOMAC knee pain (β: − 33.9, 95% CI: − 65.7, − 2) and physical dysfunction (β: − 105.5, 95% CI: − 198.2, − 12.8) than participants with vitamin D deficiency over 5 years. CONCLUSION: Vitamin D supplementation over 2 years or maintaining vitamin D sufficiency for 5 years was not associated with statistically significant differences in change in knee symptom scores over 5 years. However, among participants who did not report KS, 2-year vitamin D supplementation and maintaining sufficient vitamin D was linked to modest improvements in knee symptoms and depression scores in knee OA. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13075-023-03167-8.