Alcohol consumption in relation to breast cancer risk in a cohort of United States women 25-42 years of age

We evaluated current and past alcohol consumption prospectively in relation to breast cancer risk among 116,671 women ages 25-42 years old at enrollme nt in 1989. During 6 years of follow-up, 445 cases of invasive breast cance r were identified. For alcohol consumption in the previous year, the multiv ariate relative risk associated with more than 20 g/day (approximately 10 d rinks/week) was 1.23 (95% confidence interval, 0.68-2.21); the P for trend was 0.85. For average lifetime alcohol consumption, the multivariate relati ve risk associated with consumption of 10 or more drinks/week was 1.20 (95% confidence interval, 0.69-2.11); the P for trend was 0.18. We examined dri nking in several time periods of life; only drinking at ages 23-30 was sign ificantly positively associated with risk. Although this may represent a ch ance finding, it merits further study. Because drinking levels in this popu lation were low, we had limited information on heavier drinking. Our result s suggest that there is unlikely to be a large effect of moderate alcohol c onsumption on breast cancer risk among young women, although a modest effec t cannot be excluded. The association between alcohol consumption and breas t cancer is unlikely to be substantially stronger among premenopausal women than among postmenopausal women.