To study the association between alcohol consumption and risk of benign proliferative epithelial disorders (BPED) of the breast (conditions which are thought to have premalignant potential).

Case–cohort study.

The study was undertaken within the 56, 537 women in the Canadian National Breast Screening Study (NBSS) who completed self-administered dietary questionnaires. (The NBSS is a randomized controlled trial of screening for breast cancer in women aged 40–59 years at recruitment.)

The study subjects were the 657 women in the dietary cohort who were diagnosed with biopsy-confirmed incident BPED. For comparative purposes, a subcohort consisting of a random sample of 5681 women was selected from the full dietary cohort. After exclusions for various reasons, the analyses were based on 557 cases and 5028 non-cases.

When compared to non-drinkers, rate ratios (95%CI) for those consuming >0 and ≤10 g of ethanol day−1,>10 and≤20 g day−1, >20 and ≤30 g day1 and >30 g day1 were 0.35(0.27–0.45), 0.26(0.18–0.39), 0.29(0.18–0.48), and 0.23(0.13–0.40), respectively (the associated P value for the trend was 0.089). Similar findings were obtained from analyses conducted separately in the screened and control arms of the NBSS, in premenopausal and postmenopausal women, and for non-atypical and atypical forms of BPED, and there was little difference between the results for screen-detected and interval-detected BPED.

Alcohol consumption was associated with a non-dose-dependent reduction in risk of BPED