Oestradiol (−0.08 [−0.15: −0.02]) and SHBG (−0.19 [−0.29: −0.08]) were both inversely affected by increased childhood body size, but there was limited evidence of them affecting the risk of breast cancer (OR: 0.96 [0.68: 1.34] and OR: 0.97 [0.91: 1.04], respectively). This evidence concerns the gene SHBG and breast carcinoma.