IGF1 and colorectal carcinoma: IGF1 was found to be a plausible mediator (7% of total effects mediated, 95% CI: 2–13%, P = 0.01) in the association of genetically predicted BMI with overall CRC risk, with little evidence of residual directional pleiotropy or weak instrument bias (Fcond=46) (Figure 2 and Supplementary Table S8, available as Supplementary data at IJE online).