Several other studies have evaluated drinking at different time periods in adult life and most did not identify an association with alcohol consumption in early adult life.3, 5, 11, 21, 35-37 A meta-analysis found that studies with shorter duration of follow-up reported higher relative risks than studies with longer follow-up, suggesting that recent, rather than early, alcohol intake is more strongly associated with breast cancer risk.38 Alternatively, for studies that do not obtain updated assessments through a person's lifetime, there may be increasing misclassification of alcohol consumption as dietary patterns change with age. Our study had greater statistical power than previous studies to evaluate the effect of drinking in early adult life. We found an association of similar magnitude for early and late life, even when mutually adjusted. Our study underscores the importance of considering the totality of a woman's exposure to alcohol over her lifetime as the best measure, rather than those from one specific time period. This type of temporal relationship for alcohol intake over longer periods parallels those of hormonal influences and breast cancer risk in which the broadest consideration of hormonal influences over a lifetime most accurately reflects risk.39
