New research from Washington University School of Medicine in St. Louis links increased breast cancer risk to drinking between early adolescence and first full-term pregnancy. Previous studies have examined breast cancer risk and alcohol consumption at a later age as well as the effects of adolescent drinking on noncancerous breast diseases.

“More and more heavy drinking is occurring on college campuses and during adolescence, and not enough people are considering future risk. 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,” said co-author Graham Colditz, associate director for cancer prevention and control at Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine.

Researchers also discovered that for every bottle of beer, glass of wine or shot of liquor consumed each day, young women increase their risk of proliferative benign breast disease by 15 percent. These lesions are noncancerous, but their presence increases breast cancer risk by about 500 percent, according to first author Ying Liu, MD, PhD, a School of Medicine instructor in the Division of Public Health Sciences.

“Parents should educate their daughters about the link between drinking and risk of breast cancer and breast disease,” she said. “That’s very important because this time period is very critical.”

These findings were based on a review of the health histories of 91,005 mothers enrolled in the Nurses’ Health Study II (1989-2009). Dr. Colditz played a vital role in the development and administration of that study and other similar studies that track disease risk.

The effects of drinking at an early age in women who never had a full-term pregnancy was not considered because there was not enough representation among participants that were studied, Liu said.

Breast tissue cells are susceptible to cancer causing substances because they undergo rapid proliferation during adolescence and later in life. Further increasing the risk is the lengthening time frame between first menstrual cycle and first full-term pregnancy.

“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,” Colditz said.

Colditz believes these findings call for more research into ways that young women can counteract the adverse effects of alcohol, if they do choose to drink. Previous studies that didn’t consider alcohol use suggest that eating more fiber and exercising more lowers the risk of cancer in everyone.

This study was published online on August 28 in the Journal of the National Cancer Institute.