Alcohol consumption and risk of breast cancer: a cohort study

Objectives: To study the association between alcohol consumption and breast cancer risk. Methods: A case-cohort analysis was undertaken within the cohort of 56,837 women who were enrolled in the Canadian National Breast Screening Study (NB SS) and who completed a self-administered dietary questionnaire. (The NBSS is a randomized controlled trial of screening for breast cancer in women ag ed 40-59 at recruitment.) The cohort was recruited between 1980 and 1985, a nd during follow-up to the end of 1993 a total of 1469 women in the dietary cohort were diagnosed with biopsy-confirmed incident breast cancer. For co mparative purposes a subcohort consisting of a random sample of 5681 women was selected from the full dietary cohort. After exclusions for various rea sons the analyses were based on 1336 cases and 5238 noncases. Results: When compared to nondrinkers the adjusted incidence rate ratios (9 5% confidence intervals) for those consuming > 0 and less than or equal to 10 g of alcohol/day, > 10 and less than or equal to 20 g/day, > 20 and less than or equal to 30 g/day, > 30 and less than or equal to 40 g/day, > 40 a nd less than or equal to 50 g/day, and > 50 g/day were 1.01 (0.84-1.22), 1. 16 (0.91-1.47), 1.27 (0.91-1.78), 0.77 (0.51-1.16), 1.00 (0.57-1.75), and 1 .70 (0.97-2.98), respectively; the associated p value for the test for tren d was 0.351. Similar findings were obtained when analyses were conducted se parately in the screened and control arms of the NBSS, in premenopausal and postmenopausal women, for screen-detected and interval-detected breast can cer, and by levels of other breast cancer risk factors. Conclusions: The results of this study suggest that alcohol consumption mig ht be associated with increased risk of breast cancer at relatively high le vels of intake.