SHBG and adenoma: When additionally adjusting for C-peptide levels in model 2, the associations of free estradiol and testosterone with conventional adenoma were attenuated to null (P for trend = 0.42 and 0.27, respectively), while the associations of SHBG with conventional adenoma and serrated polyp remained essentially unchanged (P for trend = 0.0003 and 0.01, respectively) (Additional file 1: Table S6).