Scientists are calling for greater action to prevent obesity after a major study established that overweight and obese women run an increased risk of breast cancer that is not diminished by weight loss.
The study of 67,142 post-menopausal women ages 50 to 79 years old in the U.S., who were followed for a median of 13 years, ratifies that excess weight is a real risk for breast cancer. There were 3,388 breast cancers detected by 2010.
Researchers found that the cancer risk rises with greater weight and women with the most severe obesity were 86 percent more likely to develop the most common form of breast cancer, and to be diagnosed with more advanced cancers.
For the new study, published in JAMA Oncology, the researchers analyzed data from the large, long-term Women’s Health Initiative study.
The researchers grouped women by their body mass index (BMI), a measure of weight in relation to height. While a BMI of less than 25 it is considered normal, whereas it is considered overweight when BMI is between 25 and 30 and over 30 is obese. A BMI of 35 (the equivalent of a five-foot six-inch person weighing 216 pounds) or above is considered severely obese.
During the study period, it is around 5 percent of women in each weight group were diagnosed with an invasive breast cancer, but the risk of breast cancer increased with weight.
What’s more in women with BMIs of 35 and up were about 56 percent more likely to be diagnosed with any type of invasive breast cancer, compared to normal-weight women.
Viewed at specific breast cancer subtypes, they learned that the most-obese women were 86 percent more likely than normal-weight women to be diagnosed with breast tumors that are fueled by the hormones estrogen and progesterone.
These so-called estrogen receptor-positive and progesterone receptor-positive breast cancers are the most common forms of the ailment. There was no link between body weight and breast cancers that are hormone receptor-negative.
The use of hormone replacement therapy after menopause did not change the relationship between breast cancer and weight, the researchers found.
The analysis did disclose that normal-weight women who gained more than 5 percent of their starting weight over the study period had a 35 percent increased risk of breast cancer.
But for women who were already overweight or obese, losing weight did not protect women from breast cancer.
While more studies need to be conducted, Dr. Clifford Hudis told Reuters Health the new results are “a caution that once you’re overweight the damage may be done.”
Hudis, who co-wrote an editorial accompanying the new study, said research also needs to find out why increased weight may increase breast cancer risk so that solutions can be found.
His research group concentrated on the potential role of inflammation generated by fat tissue, and perhaps other effects on the endocrine system that could fuel cancer growth.