The causal relationship between serum 25-hydroxy vitamin D and allergic rhinitis：A two-sample bidirectional Mendelian randomization analysis

Objective: To evaluate the causal relationship between serum 25-hydroxy vitamin D [25(OH)D] and Allergic Rhinitis (AR) by two-sample bidirectional Mendelian randomization (MR).Methods: Genetic data of serum 25(OH)D and AR were respectively obtained from UK Biobank and Finn Gen, selecting appropriate SNPs as instrumental variables. Five methods, including Inverse variance weighted method (IVW), MR-Egger method, Weighted median method (WM), Simple mode method, and Weighted mode method, were used for bidirectional MR analysis, with performing sensitivity analysis, heterogeneity test, and horizontal pleiotropic analysis.Results: IVW results showed that there was a causal association between serum 25(OH)D levels and AR. Lower serum 25(OH)D levels increased the risk of allergic rhinitis (OR=0.819, 95%CI 0.694~0.968, P=0.019), and patients with AR exhibited lower levels of serum 25(OH)D (OR=0.935, 95%CI 0.896~0.975, P=0.002). The forward and reverse MR analyses exhibited heterogeneity, while no evidence of horizontal pleiotropy was observed. The results obtained through the residual one method remained robust and reliable after gradual elimination of single SNPs.Conclusions: A causal relationship exists between serum 25(OH)D levels and allergic rhinitis. Reduced serum 25(OH)D levels are a risk factor for the development of allergic rhinitis, and patients with AR have a higher prevalence of 25(OH)D deficiency.