Background Clinical studies involving observation have uncovered a mutual relationship between allergic disorders and diabetes, yet the precise causal link remains undetermined. Methods We conducted two-sample bidirectional Mendelian randomization analyses using single nucleotide polymorphisms (SNPs) associated with allergic conditions (asthma, allergic rhinitis, atopic dermatitis) from genome-wide studies and SNPs related to type 2 diabetes from FinnGen. Initially, we evaluated the causal link between allergic disorders and type 2 diabetes through a univariate Mendelian randomization study, incorporating inverse variance weighting, MR-Egger, and the weighted median estimator. To address potential confounding, we employed multivariate Mendelian randomization. Finally, we validated mediators influencing the correlation between asthma and type 2 diabetes. Results The Inverse variance weighte method showed that asthma genetically increased the risk of type 2 diabetes (Asthma- type 2 diabetes: β(95%CI)=0.892(0.152~1.632), P = 0.018). Allergic rhinitis and type 2 diabetes exhibit a mutual protective effect: β(95% CI)=-1.333(-2.617 to -0.049), P = 0.042;type 2 diabetes - Allergic rhinitis: β(95%CI)=-0.002(-0.004 to -0.000), P = 0.018). The Multivariable Mendelian randomization study results showed that after after excluding confounding factors, asthma still demonstrates statistical significance in relation to type 2 diabetes. Through mediation analysis, it was discovered that lung function and the percentage of monocytes in leukocytes exert an inhibitory effect on the mediation between asthma and type 2 diabetes. Conclusion The Multivariable Mendelian randomization study indicates asthma as a risk factor for type 2 diabetes.Lung function, and the percentage of monocytes in leukocytes, play an inhibitory role in asthma and type 2 diabetes mediating effects.
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