The risk for breast cancer among obese women may be up to 58 percent higher than for normal-weight postmenopausal women, according to a report published in JAMA Oncology.
Marian Neuhouser, a professor of epidemiology at the Fred Hutchinson Cancer Research Center in Seattle, Ph.D., R.D., and colleagues collected data on 67,142 postmenopausal women who took part in the Women’s Health Initiative from 1993 to 1998. During an average 13 years of follow-up, more than 3,388 women developed breast cancer.
The researchers found that women who were overweight and obese had an increased invasive breast cancer risk compared to women of normal weight, with greater risk for more severe obesity.
Very obese women were at increased risk for estrogen- and progesterone-driven breast cancer, but not for other types. These women were also at increased risk of larger tumors and death.
Women with a baseline body mass index of less than 25.0 kg/m² who gained more than 5 percent of their body weight over the years of the study also had an increased risk for breast cancer; however, women already overweight or obese did not.
“Obesity is known to increase estrogens in the postmenopausal women because estrogen is made by fat tissue,” Neuhouser told HealthDay. “Fat tissue also secretes inflammatory factors and is associated with insulin resistance — all of which may increase breast cancer risk.”