Excessive alcohol consumption increases breast cancer risk, says a new study published online in the European Journal of Public Health (April 18, 2007).

Researchers in Denmark collected lifestyle data on 17,647 nurses, ages 44 and older, beginning in 1993. During eight years of follow-up, 457 women were diagnosed with breast cancer.

Drinking patterns played an important role, scientists found. Binge drinking on a weekday (four to five drinks) was associated with a 55 percent increased risk of breast cancer compared to those who had only one drink per weekday.

The amount of alcohol consumed was another important risk factor. Women who consumed 22 to 27 drinks per week had more than twice the risk of breast cancer than women who drank only 1 to 3 drinks per week. Interestingly, breast cancer risk increased 2 percent for every additional drink during the week and 4 percent for each extra drink on the weekends.

"Binge drinking and weekend consumption are associated with peaking levels of the alcohol concentration in the blood," says study leader Lina Morch, MSc, and PhD student. "Studies have suggested that the peaking levels of alcohol concentration can also cause a higher concentration of estrogens, which are known risk factors for breast cancer."

According to the National Institutes of Health, of the 60 percent of American women who drink, 13 percent have more than seven drinks per week and an estimated 5.3 million are heavy drinkers.