LEP and breast cancer: In unadjusted models, statistically significant heterogeneity by BMI was found for leptin and leptin-to-adiponectin ratio (Phomogeneity=0.03 and Phomogeneity=0.03, respectively; Additional file 1: Table S5) suggesting a higher breast cancer risk among women with BMI ≥ 25kg/m2 [OR1SD =1.10 (1.01–1.20) and OR1SD =1.08 (0.99–1.18), respectively] but not among women with BMI < 25 kg/m2 [OR1SD =0.97 (0.89–1.05) and OR1SD =0.96 (0.88–1.04), respectively].