Dietary folate intake, alcohol, and risk of breast cancer in a prospectivestudy of postmenopausal women

Low B-vitamin intake may increase risk of breast cancer through decreased D NA repair capacity. Alcohol intake increases risk for breast cancer, with e vidence from prospective studies of an interaction between alcohol and fola te, We explored dietary intake of folate and other B vitamins with risk of breast cancer in a cohort study of 34,387 postmenopausal women. To measure diet, we mailed a food frequency questionnaire; we estimated nutrient intak es and categorized them into four levels: < 10th, 11th-30th, 31st-50th, and > 50th percentiles. Through 12 years of follow-up. we identified 1,586 cas es of breast cancer in the cohort at risk. We estimated relative risks (RRs ) and 95% confidence intervals (CIs) through Cox regression models adjusted for age, energy, and other risk factors. Women in the lowest 10th percenti le of folate intake from diet alone were at modestly increased risk of brea st cancer relative to those above the 50th percentile: RR = 1.21 (95% CI = 0.91-1.61). We examined the joint association of folate intake and alcohol use on risk of breast cancer, with the reference group defined as women wit h high folate (> 50th percentile) and no alcohol use. The RRs of breast can cer associated with low dietary folate intake were 1.08 (95% CI = 0.78-1.49 ) among nondrinkers, 1.33 (95% CI = 0.86-2.05) among drinkers of less than or equal to4 gm per day, and 1.59 (95% CI = 1.05-2.41) among drinkers of >4 gm per day. These results suggest that the risks of postmenopausal breast cancer may be increased among women with low intakes of folate if they cons ume alcohol-containing beverages.