Serum vitamin D levels and Sjogren's syndrome: bi-directional Mendelian randomization analysis

Based on the results of existing observational studies, it can be found that the association between serum vitamin D levels and the risk of Sjogren's syndrome (SS) in humans is still controversial. Based on this situation, this study aimed to assess the causal relationship between serum vitamin D levels and SS by using the Mendelian randomization (MR) approach.

In this study, genome-wide association studies (GWAS) summary statistics on serum vitamin D levels [sample size = 417,580 (UK Biobank)] and SS [sample size = 416,757 (cases = 2495, controls = 414,262) (FinnGen)] were used. The bi-directional MR analysis was then used to assess possible causal relationships. The major analysis method of MR was performed using inverse-variance weighted (IVW), supplemented by MR-Egger and the weighted median approaches. In addition, sensitivity analyses were used to ensure the stability of the results, including Cochran's Q test, MR-PRESSO, MR-Egger intercept test, and the leave-one-out test.

The MR suggested that no significant causal effects of serum 25(OH)D levels on SS risks were observed [odds ratio (OR) = 0.9824; 95% confidence interval (CI) = 0.7130 to 1.3538; P = 0.9137]. Similarly, no evidence supported the causal effects of SS on serum vitamin D levels (β: 0.0076, 95% CI: - 0.0031 to 0.0183; P = 0.1640).

This study found no obvious evidence that serum vitamin D level is causally associated with SS risks or vice versa. We call for larger sample size studies to further unravel the potential causal relationship and the exact mechanism.