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Drinking alcohol before pregnancy may increase a woman's risk of breast cancer and benign breast disease, new research suggests.

Previous studies revealed that alcohol consumed in the past year affects a woman's breast cancer risk. However, the link between alcohol consumption during the period of time between a woman's first menstrual period and first pregnancy and the risk of proliferative BBD and breast cancer had not been reported.

Researchers wanted to look at the link between alcohol consumption before pregnancy and cancer risk in women because they say breast tissue is particularly susceptible to carcinogens during that period of time.

The latest study analyzed data from 116,671 female registered nurses, aged 25-44 years, on medical history, reproductive history, and lifestyle. After excluding women who did not meet the predetermined study criteria, a total of 91,005 women with a history of full-term pregnancy were included in the final analysis.

Among the women who were included in the study, 1,609 developed breast cancer and 970 developed BBD during the study period.

The findings revealed that drinking alcohol before the first menstrual period and first pregnancy was significantly associated with risk of breast cancer and proliferative BBD, regardless of drinking after the first pregnancy.

Furthermore, researchers found a dose-dependent relationship between alcohol consumption and breast cancer, meaning that the more alcohol a woman drinks during that time, the higher her risk of developing breast cancer.

The study also found that longer intervals between first menstrual period and first pregnancy showed stronger associations compared with shorter intervals.

Researchers also linked drinking after the first pregnancy to an increased risk of breast cancer, but not BBD.

"The general consistency in the patterns of association between alcohol and risk of proliferative BBD and of breast cancer lends support to the hypothesis that alcohol intake, particularly before first pregnancy when breast tissue is likely at its most vulnerable stage, may play an important role in the etiology of breast cancer," researchers wrote in the study.

Researchers said the latest findings, published in the Journal of the National Cancer Institute, might have important implications for breast cancer prevention.