Alcohol and breast cancer risk--putting the current controversy into perspective.

The potential association of alcohol intake with breast cancer risk is currently being debated in the literature and a clear consensus of opinion has not emerged. Clarification of the issues surrounding this controversy would be helpful in developing recommendations for the general public regarding alcohol use. A review of the available evidence regarding the association of alcohol with breast cancer is presented followed by an application of the Bradford Hill criteria for causal inference to this data to examine the existence and nature of the association of alcohol with breast cancer risk. Results of published studies demonstrated a weak association of alcohol with breast cancer risk that was consistent only for relatively high levels of intake (more than 1 or 2 drinks daily). Increasing daily intake was associated with increased risk, but the association was not linear. Criteria relating to temporality and analogy to other causal associations were satisfied while inconsistent evidence was available for those relating to epidemiologic and biologic sense. The criterion for specificity was not satisfied and no experimental evidence was available. It is concluded that insufficient evidence exists to support a causal association of alcohol consumption with breast cancer risk. Further research is recommended to resolve conflicting evidence and to provide additional evidence where needed. In the meantime, recommendations that women should reduce their consumption of alcohol beyond existing guidelines to modify breast cancer risk are probably premature.