The theory that a high-fat diet places women at higher risk for developing breast cancer is the subject of ongoing studies. Regardless, the connection between low-fat diets and lower incidences of heart disease and colon cancer indicate the health benefits of controlling fat intake. Research has shown that women who consume two to five alcoholic drinks daily have a higher incidence of breast cancer than women who do not drink at all. There is some indication that higher levels of circulating estrogen may contribute to the development of breast cancer. This may be due to the fact that intense exercise reduces circulating estrogen levels, causing women who exercise to begin menstruating at a later age than average.
Research is ongoing.
Women who are overweight have a higher risk of breast cancer. Postmenopausal women who had never taken hormone replacement therapy showed the strongest association in this study. Of these women, those who had a waist circumference of between 32 and 35.9 inches, and between 36 and 55 inches, had a higher risk of breast cancer than women with a waist circumference between 15 and 27.9 inches. It is suspected that the increased risk may result from excess abdominal fat, which is believed to be associated with higher levels of estrogen in the blood. Alcohol combined with the estrogen in HRT appears to increase the level of circulating estrogen in the bloodstream, which may be the reason for the higher risk among these women.