Before sending their daughters off to college, parents should discuss yet another important issue with them: how much they drink could increase their risk of breast cancer. 

Researchers at Washington University School of Medicine in St. Louis found that every drink—whether beer, wine, or liquor—a young woman consumes daily before her first pregnancy puts her at a nearly 15 percent greater risk of developing proliferative benign breast disease, a noncancerous breast condition linked to breast cancer. 

In fact, the presence of the noncancerous breast lesions raises a woman's risk of breast cancer by up to 500 percent.

While men have have historically been bigger college boozers than women, the gender gap is closing, as 40 percent of college-age women now report binge-drinking habits, according to the National Survey on Drug Use and Health. For women, binge drinking is consuming four or more alcoholic beverages in one sitting. 

Dr. Graham Colditz, co-author of the study and associate director for cancer prevention and control at Siteman Cancer Center at Barnes-Jewish Hospital, said that while heavy drinking is occurring on college campuses, more young women need to consider the health risks. 

His lesson to those studying for their future 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,” he said.

Researchers studied the health records of 91,005 mothers in the Nurses' Health Study II, a 20-year study designed to examine the long-term use of oral birth control. Adjusting for modern rates, the study found five percent of  the estimated 232,340 breast cancer diagnoses in 2013 would not occur if the woman didn't heavily drink alcohol before her first pregnancy.

While other research has indicated that alcohol is a risk factor for breast cancer, this was the first study to examine alcohol’s effect during a time when breast cells are undergoing rapid proliferation and are therefor more vulnerable to cancer-causing substances.  

"Parents should educate their daughters about the link between drinking and risk of breast cancer and breast disease. That's very important because this time period is very critical," said Dr. Ying Liu, a Washington University instructor in the Division of Public Health Sciences.

Women who had their period before age 12 and their first child after 35 are at a greater risk of breast cancer than other women. 

Researchers noted that the average time from a woman’s first menstrual cycle to first full-term pregnancy doesn’t seem to be shortening, so that’s another reason for women to lower their average daily consumption below one drink. 

The research was published online in the Journal of the National Cancer Institute and supported by the National Cancer Institute and National Institutes of Health. 

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