The strengths of this study include the large number of cases, length of follow-up, and detailed prospective and updated assessments of alcohol consumption across different age periods affording the most comprehensive evaluation of the effect of alcohol consumption throughout a woman's life. Limitations include that this was an observational study, so alcohol use was not randomly assigned to women. However, it is unlikely that such a long-term randomized trial will ever be performed. We relied upon self-reported alcohol use, but this has previously been shown to be highly reproducible within our cohort and strongly correlated with HDL levels.16 We have also previously demonstrated that measurement error does not strongly affect our estimates of the alcohol association.40 Compared to some studies done in Europe, we do not have as many women with higher levels of alcohol consumption. However, the distribution of alcohol intake in NHS is fairly similar to that of US women.41 Our study population was predominantly White, but the limited available data suggest that the associations between alcohol and breast cancer does not differ by ethnicity.42 The referent group
