Impact of season on the association between vitamin D levels at diagnosis and one-year remission in early Rheumatoid Arthritis

The study evaluates associations between serum vitamin D metabolites at diagnosis and one-year remission, in early diagnosed rheumatoid arthritis(RA). The CIMESTRA-cohort comprised 160 newly diagnosed RA patients, treated aiming at remission. Vitamin D supplementation was recommended according to national guidelines. Dtotal(25OHD2 + 25OHD3) was dichotomized at 50 nmol/L, 1,25(OH)2D was categorized in tertiles. Primary outcome was remission(DAS28-CRP ≤ 2.6) after one year. Associations were evaluated using logistic regression, further adjusted for pre-specified potential confounders: Age, sex, symptom-duration before diagnosis, DAS28-CRP and season of diagnosis. Results are presented as Odds Ratios(OR) with 95% Confidence Intervals(95%CIs). In univariate analyses, neither Dtotal nor 1,25(OH)2D were associated with remission. In adjusted analyses, low Dtotal was associated with higher odds for remission; OR 2.6, 95%CI (1.1; 5.9) p = 0.03, with season impacting results the most. One-year remission was lower in patients with diagnosis established at winter. In conclusion, low Dtotal at diagnosis was associated with increased probability of achieving one-year remission in early RA when adjusting for covariates. Diagnosis in winter was associated with lower odds for one-year remission. Results suggest that season act as a contextual factor potentially confounding associations between vitamin D and RA disease-course. The finding of low Dtotal being associated with higher one-year remission remains speculative.