Association between vitamin D deficiency and the 8-year risk of incident depression in patients with rheumatoid arthritis: a cohort study.

Background: Depression is common among patients with rheumatoid arthritis (RA) and is associated with adverse clinical outcomes. Vitamin D deficiency (VDD) is also prevalent in patients with RA and has been linked to depressive symptoms in cross-sectional studies; however, longitudinal data on its association with incident depression are limited. Methods: We conducted a retrospective cohort study using the TriNetX Global Collaborative Network (2010-2024). Adults with RA and serum 25-hydroxyvitamin D levels were identified and classified as having VDD (<20 ng/mL) or sufficient vitamin D levels (≥30 ng/mL). After 1:1 propensity score matching for demographics, comorbidities, medications, and laboratory variables, 18,339 patients were included in each group. A 180-day landmark period was applied to strengthen the temporal ordering. The primary outcome was the incidence of depression. The secondary outcomes included antidepressant use, suicide-related events, and all-cause mortality. Negative and positive control outcomes were also examined. Results: Compared with sufficient vitamin D levels, VDD was associated with a higher risk of incident depression (HR 1.64, 95% CI 1.50-1.78; Conclusion: Among patients with RA, VDD was associated with a higher long-term risk of incident depression. These findings support a possible association between vitamin D status and depression risk in this population; however, a causal inference cannot be established from this observational study.