Purpose: Moderate alcohol intake of one to two drinks per day has been consistently associated with a 30-50% increase in breast cancer. Despite the consistency in the overall association, several important questions remain, including whether the association between alcohol intake and breast cancer risk is affected by the timing of alcohol exposure, modified by other risk factors such as body mass index (BMI), menopausal status, and hormone replacement therapy (HRT), or more pronounced among hormone receptor positive tumors or invasive rather than in situ disease.
Methods: To address these questions, we conducted a large population-based study (1508 cases and 1556 controls) that collected detailed information on alcohol and other exposures throughout the lifecourse.
Results: Consumption of 15-30 grams/day (approximately one to two drinks) throughout life was associated with a modest 33% increase in risk (odds ratio [OR] = 1.33, 95% confidence interval (CI) = 1.01-1.74), but heavier consumption (> or = 30 grams per day) was not. Risk did not vary with alcohol type (beer, wine, or hard liquor) or by patterns of use, such as recent use, intake prior to age 20 years, or whether use began at an early age. The association with lifetime intake was limited to women with a BMI < 25 (OR = 2.13, 95% CI = 1.29-3.54). Alcohol consumption of approximately one drink per day was associated with estrogen receptor positive tumors among women with a BMI < 25, but not among women BMI > or = 25. Also, the elevated OR was observed only among women diagnosed with invasive (OR = 1.56, 95% CI = 1.11-2.18), but not in situ breast tumors.
Conclusions: These data give added support that moderate alcohol consumption over the life course increases breast cancer risk, particularly among women with low BMI and those diagnosed with estrogen receptor positive tumors or with invasive rather than in situ disease. Risk is confined to moderate intake and does not vary with the timing of use, with heavier doses, or with the type of alcohol consumed.