SHBG and polycystic ovary syndrome: Taken together, we found the following two potential mediation pathways between NAFLD and PCOS: (1) an indirect causal effect of NAFLD on PCOS risk via fasting insulin levels only (θ2×θ6) (OR: 1.02, 95% CI: 1.01–1.03; P = 0.004) and (2) a suggestive indirect causal effect of NAFLD on PCOS risk via circulating levels of fasting insulin, SHBG, and bioavailable testosterone (θ3×θ4×θ5×θ6) (OR: 1.0025, 95% CI: 1.0002–1.0049; P = 0.0323) (Additional file 1: Table S11).