BETHESDA, Md--The latest major study of the relationship between diet and breast cancer risk has introduced an intriguing but somewhat complex element into this enduring controversy.
After analyzing data gathered from women enrolled in the Nurses' Health Study, including 2,500 with breast cancer, a team of Harvard University researchers has concluded that weight gain after age 18 increases a woman's risk of developing mammary tumors following menopause.
"There is a very strong relationship between weight gain and breast cancer," said Walter C. Willett, MD, DrPH, of Harvard's School of Public Health. His group found scant support, however, for the notion that high levels of dietary fat by themselves boost a woman's risk. "It's not fat per se that seems to be important; it's calories," he said.
The study also confirmed earlier studies showing that alcohol(Drug information on alcohol) use--as few as one or two drinks a day--and taller stature increase breast cancer risk, Dr. Willett said at the General Motors Cancer Research Foundation annual conference.
A weight gain of 20 kg (44 lb) beginning in early adulthood doubled the likelihood of a postmenopausal diagnosis of breast cancer, the Harvard team found. An increase of 10 kg (22 lb) boosted a woman's risk by 70%.
Gaining weight increases estrogen in the body, Dr. Willett noted. Thus, the pounds added by women in the study probably heightened their risk of post-menopausal breast tumors by contributing to higher endogenous estrogen levels, he said. However, the risk profile proved complicated.
Increased weight after age 18 slightly lowered a woman's risk of developing breast cancer before menopause, perhaps, Dr. Willett speculated, because overweight women have more anovulatory menstrual cycles. But this lower breast cancer risk did not translate into a decreased risk of dying from the disease.