2.2 Data sources
Each bacterial taxon was regarded as a separate exposure. Following multiple steps, the instrumental variables of each bacterial taxon were acquired from the largest genome-wide association study (GWAS) of human gut microbiota, which comprised 18340 individuals from 24 cohorts, 14363 (>78%) were European ethnic participants [12]. The data could be derived athttps://mibiogen.gcc.rug.nl/. A total of 196 gut microbiota were selected after excluding 15 bacterial taxa with unknown family or genus (Supplementary Table 1), which finally included 9 phyla, 16 classes, 20 orders, 32 families, and 119 genera. MN was regarded as the outcome variable in this study. The SNPs were acquired from the website:https://gwas.mrcieu.ac.uk/datasets/ebi-a-GCST010005/. The GWAS data of MN included nine case-control cohorts composed of 4841 East Asian and 7979 European populations.