A diet too high in calories, which leads to obesity, increases breast cancer risk. Postmenopausal obesity increases breast cancer risk because the aromatase enzyme system in fat cells causes more estrogen to be formed. Children who are obese develop menstrual cycles an early age, also increasing breast cancer risk.
Drinking alcohol in any form, beer, wine or spirits, increases breast cancer risk through its effect upon the liver. The liver metabolizes estrogen and can change it into an inactive form.
A liver impaired by alcohol lets estrogen build to higher levels, thereby stimulating the breast. For example, men who are alcoholics develop increased breast tissue, called gynecomastia, from elevated estrogen levels.