Drinking has become a pastime at some U.S. universities, but women who drink heavily in the years leading up to motherhood could be putting themselves at risk. A new study has linked drinking before childbirth to an increased risk of breast cancer.

The study, published in the Journal of the National Cancer Institute, has shown that women who drink more in the time between puberty and their first pregnancy have a significantly higher risk of developing breast cancer. Researchers looked at over 91,000 mothers in a study spanning the years 1989 to 2009.

“More and more heavy drinking is occurring on college campuses and during adolescence, and not enough people are considering future risk,” said Dr. Graham Colditz, a co-author the study and an associate director for cancer prevention and control at the Washington University School of Medicine. “But, according to our research, the lesson is clear: If a female averages a drink per day between her first period and her first full-term pregnancy, she increases her risk of breast cancer by 13 percent.”

The study also found that drinking the equivalent of one drink per day increased the risk of non-cancerous breast disease lesions, which also increase breast cancer risks. Researchers were not able to determine whether the risk still increases for women who do not go on to have children, as too few women in the study were non-mothers.

The researchers stated that female breast tissue is “particularly susceptible” to carcinogens as they go through puberty and early adulthood. They recommend reducing alcohol consumption to cut breast cancer risks later in life.

“Reducing drinking to less than one drink per day, especially during this time period, is a key strategy to reducing lifetime risk of breast cancer,” said Colditz.