Fig. 1

Related databases and analysis methods in MR analysis. The publicly available summary data of SNP phenotypes were obtained from the largest meta-GWAS databases. The effect of iron status on asthma was estimated using a conservative approach (IVs: only SNPs connected with the concentrations of ferritin, serum iron and transferrin saturation were increased, concentrations of transferrin was decreased and systemic iron status would be increased) and a liberal approach (IVs: one of the SNPs was associated with breast cancer). In conservative instruments set, the inverse-variance-weighted (IVW) method was used, and in liberal instruments set, the IVW, MR Egger regression, weighted median and simple mode methods were used. MR, Mendelian randomization; IVs, instrumental variables; SNP, single nucleotide polymorphism; MR Egger, Mendelian randomization–Egger regression method; BMI, body mass index