Is Vitamin D Deficiency the Cause or the Effect of Systemic Lupus Erythematosus: Evidence from Bidirectional Mendelian Randomization Analysis.

Background. Vitamin D deficiency is common in patients with systemic lupus erythematosus (SLE). Observational studies have reported that it is associated with SLE. In this bidirectional Mendelian randomization (MR) study, we explored the genetic association between serum vitamin D (VD) levels and SLE using two models. Methods. Genetic variants associated with vitamin D (n=304,181), 25-hydroxyvitamin D levels (n=401,460), and SLE (n=213,683) at genome-wide significance (P