Cao M, et al. - This investigation was undertaken to determine if age at menarche (AAM) was causally correlated with type 2 diabetes (T2D), coronary artery disease (CAD) and cardiometabolic traits using Mendelian randomization (MR). In order to determine the causal effect of AAM on cardiometabolic diseases, treating childhood and adult BMI as the confounders, 122 instrumental variables (IVs) were used extracted from a published genome-wide association study meta-analysis including 182,416 women. In addition, sensitivity analyses were conducted to identify the pleiotropy of the IVs. The results demonstrated that AAM did not seem to have a causal effect on the adult life risk of cardiometabolic diseases since their associations found in epidemiological studies could be largely mediated by excessive adiposity. In future intervention strategy, adiposity might be a primary target.