School-age drinking increases breast cancer risk​​​​​​

That's according to new research from Washington University School of Medicine in St. Louis that, for the first time, links increased breast cancer risk to drinking between early adolescence and first full-term pregnancy. Previous studies have looked at breast cancer risk and alcohol consumption later in life or at the effect of adolescent drinking on noncancerous breast disease.

"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, MD, DrPH, associate director for cancer prevention and control at Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine.

The study is published online Aug. 28 in the Journal of the National Cancer Institute.

Colditz also is the Niess-Gain Professor of Surgery at Washington University School of Medicine. He worked on the study with first author Ying Liu, MD, PhD, a School of Medicine instructor in the Division of Public Health Sciences, and colleagues from Brigham and Women's Hospital, Harvard Medical School, Beth Israel Deaconess Medical Center and Harvard School of Public Health.

The researchers also found that for every bottle of beer, glass of wine or shot of liquor consumed daily, a young woman increases her risk of proliferative benign breast disease by 15 percent. Although such lesions are noncancerous, their presence increases breast cancer risk by as much as 500 percent, Liu said.

"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."

The findings are based on a review of the health histories of 91,005 mothers enrolled in the Nurses' Health Study II from 1989 to 2009. Colditz was key to the development and administration of that and similar studies that track disease risk in female nurses.

Colditz and Liu didn't consider the effects of adolescent and early adulthood drinking on women who didn't have a full-term pregnancy because not enough were represented among those studied, Liu said.

Breast tissue cells are particularly susceptible to cancer-causing substances as they undergo rapid proliferation during adolescence and later. Adding to the risk is the lengthening time frame between the average age of a girl's first menstrual cycle and the average age of a woman's first full-term pregnancy. Colditz doesn't foresee any shortening of that, which is why young women should drink less, he said -- to lower average daily consumption and, therefore, risk.

"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," he said.

Colditz said the findings call for more research into what young women can do to counteract alcohol's adverse effects if they choose to drink. Past studies that didn't consider alcohol use suggest that eating more fiber and exercising more lowers cancer risk for everyone.