Alcohol and breast cancer mortality in a cohort study.

Available epidemiological evidence indicates that alcohol intake is associated with a higher risk of developing breast cancer. Plausible biological pathways include its effect on levels of estrogens, cell membrane integrity and cell-to-cell communication, inhibition of DNA repair, and congener effect. The present study evaluated the impact of alcohol on mortality from breast cancer, an area with relatively few studies in the literature. The subjects were participants in a Canadian prospective cohort study, the National Breast Screening Study (NBSS). Women were enrolled in the cohort from 1980 to 1985 to evaluate the efficacy of mammographic screening. Information on usual diet and alcohol intake at enrolment and other epidemiological variables was collected by means of a mailed, self-administered questionnaire. Mortality from breast cancer during follow- up to 31 December, 1993 was ascertained by record linkage to the Canadian Mortality Data Base maintained by Statistics Canada. During the follow-up period of 1980-1993 (average 10.3 years), 223 deaths from breast cancer were identified for this analysis. The hazard ratios for the risk of death from breast cancer increased with intakes of total alcohol of 10-20 g/day (1.039, 1.009-1.071) and > 20 g/day ( 1.063, 1.029-1.098). This increase was contributed largely by the intake of wine, a 15% increase in risk at intakes higher than 10 g/day of alcohol from wine. Alcohol from spirits was associated with a small decrease in risk of death (hazard ratio at 10g/day, 0.945, 0.915-0.976). The effect of alcohol from beer was not significant in the two categories studied. Although our results were statistically significant, the magnitude of the change in risk was small.