Alcohol consumption and risk of breast cancer.

In a national case-control study, 891 New Zealand women aged 25 to 54 with newly diagnosed breast cancer were compared with 1,864 control subjects selected at random from the electoral rolls. The relative risk of breast cancer for current drinkers of alcohol, compared with women who had never drunk alcohol, was 1.0 (95% confidence interval 0.64 to 1.7). For ex-drinkers the relative risk was 1.3 (95% confidence interval 0.74 to 2.5). Women drinking up to 14 drinks per week had no increase in risk, while the relative risk in those consuming more than 14 drinks per week was 1.8 (95% confidence interval 0.87 to 3.8). There was no evidence of effect modification by age at diagnosis, menopausal status, body mass index, or any of the other variables examined. While these results provide little support for the hypothesis that moderate alcohol consumption increases the risk of breast cancer, they are not inconsistent with the weak associations that have been found in many other studies. Possible explanations for such a relationship are considered.