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Young women who regularly drink alcohol before their first pregnancy may be increasing their risk for breast cancer, a new study reports.

The prospective study of more than 150,000 women with no history of cancer also found that alcohol use before pregnancy was associated with an increased risk for proliferative benign breast disease, or B.B.D., noncancerous breast abnormalities that also raise the risk for cancer.

The study, published online in The Journal of the National Cancer Institute, found 1,609 cases of breast cancer and 970 of B.B.D. over a 20-year follow-up.

After adjusting for other factors, they found that compared with not drinking, having 10 grams of alcohol six times a week (a standard drink contains about 14 grams of alcohol) was associated with an 11 percent increase in breast cancer and a 16 percent increase in B.B.D. The association grew stronger with increasing amounts of alcohol and time between a girl’s first period and her first pregnancy.

“Limiting alcohol can pay off through reduced breast cancer risk,” said Dr. Graham A. Colditz, a co-author of the study, “and this interval in adolescence and young adulthood is extremely important for setting the lifetime risk for breast cancer.” Dr. Colditz is a professor of surgery at Washington University in St. Louis.

Breast tissue in women who have not been pregnant is particularly susceptible to carcinogens, the authors write, which might help explain the greater adverse effect of drinking before pregnancy.