Alcoholic beverage consumption and breast cancer incidence.

Recent case-control studies have suggested that alcohol consumption may be associated with breast cancer incidence. This report is a retrospective cohort study of over 95,000 women who were members of the Kaiser Foundation Health Plan of Northern California. The stated alcohol consumption of these women was recorded at a multiphasic screening examination taken from 1964 to 1972 prior to any diagnosis of breast cancer. The incidence of breast cancer in this cohort was greater for women who drank, and among these drinkers, incidence increased in an irregular trend with heavier alcohol consumption. Control for the effects of race, education, smoking, and reproductive variables related to breast cancer all but eliminated the overall increased relative risk of drinkers compared with that of nondrinkers. However, the relatively small group of women who stated that they had three or more alcoholic drinks per day (5.2 per cent of the total) had a significantly elevated relative risk of 1.4 (p = 0.035) compared with nondrinkers, despite control for all available confounding variables. No significant interaction effect of smoking and alcohol was found. Women who had less than three drinks per day had no increased relative risk over nondrinkers. The results of this study might be explained either by an unrecognized carcinogenic effect of alcohol on breast tissue or by the confounding effect of other factors associated with heavy alcohol use.