[Alcohol and risk of breast cancer. Studies published between 1988 and 1993]

Epidemiological studies have suggested that moderate intake (1-2 drinks per day) of alcohol may increase the risk of breast cancer by more than 50%. A relatively large proportion of women in many countries consume alcohol at this level, and a precise assessment of the related breast cancer risk is therefore important. In this paper we have reviewed all published studies subsequent to a comprehensive meta-analysis on alcohol and breast cancer, published in 1988. Among four cohort studies, the relative risk of breast cancer associated with 1-2 drinks per day (compared with no drinking) varied between 1.0 and 1.3, and the null value of 1.0 was included in the 95% confidence interval for each of the studies. For consumption higher than two drinks per day, two of the four cohort studies indicated a significantly increased risk. Among 14 case-control studies, the point estimates showed increased breast cancer risk in 11, and five were statistically significant. Three studies indicated a negative association, but the confidence interval included 1.0 in two of them. Among case-control studies which provided information on intakes higher than two drinks, eight out of 13 studies showed a statistically significant positive association. Collectively these studies support a weak positive association between moderate consumption of alcohol and breast cancer risk. The tendency between studies is consistent, but the precision of the estimate of relative risk is low in most studies. Unless consumption is two drinks or higher per day, no recommendation to reduce drinking should be made based on the present evidence relating alcohol consumption to breast cancer risk.