Vitamin D and risk of ankylosing spondylitis: A two-sample mendelian randomization study.

Objectives: To study whether Vitamin D levels are causally associated with ankylosing spondylitis (AS).

Methods: Two-sample Mendelian randomization (TSMR) analysis was performed by employing MR-Egger regression, weighted median (WM), inverse-variance weighted (IVW), and weight mode (WM) methods. The odds ratio (OR) with 95% confidence intervals (CIs) was used to evaluate this association.

Results: The results of IVW show that no causal association between vitamin D and AS (OR = 0.999, 95%CI = 0.997, 1.002, P = 0.724). The MR-Egger regression results show that genetic pleiotropy does not bias the results (intercept = -4.474E-05, SE = 2.830E-05, P = 0.255). The MR-Egger method no supported causal association between vitamin D and AS (OR = 1.000, 95%CI = 0.996, 1.005, P = 0.879). WM (OR = 1.002, 95%CI = 0.999, 1.005, P = 0.837) and WM (OR = 0.998, 95%CI = 0.996, 1.002, P = 0.910) approach also not found a causal relationship between vitamin D levels and AS. The significant heterogeneity was not observed by Cochran's Q test. The "leave-one-out" analysis also proved lack of a single SNP affected the robustness of our results.

Conclusion: Based on our analysis, there is lack of a strong evidence to support a causal inverse association between vitamin D levels and ankylosing spondylitis.