Although the exact mechanism for the alcohol and breast cancer association is not known, one probable explanation would involve alcohol's effects on circulating estrogen levels. Most other large studies have shown a stronger association with ER+ breast cancers.8, 9, 20-24 In short-term feeding studies, moderate levels of alcohol consumption increased circulating sex hormone levels in both pre- and postmenopausal women. 25, 26 Cross-sectional studies also support a positive association between alcohol consumption and plasma sex hormone levels.27, 28 Alcohol may increase sex hormone levels in several ways: increased aromatase activity 29, decreased hepatic catabolism of androgens30 or effects on adrenal steroid production26. In vitro studies have demonstrated that alcohol can increase the transcriptional activity of ER-α31 (which may influence breast tissue's sensitivity to estrogens) and preferentially enhance proliferation and ER-α content in ER+ cell lines.32
