The Grapevine

In Young Women, Obesity Linked To Lower Risk Of Breast Cancer

According to U.S. statistics, nearly 1 in 8 women develop invasive breast cancer over the course of their lifetime. Some of the risk factors include family history, ethnicity, alcohol use, smoking, physical activity, etc.

Combining the factors of age and body mass index (BMI), it is noted older women who gain extra weight also have a higher risk. But the latest research led by the National Institutes of Health focused on how obesity in younger women can affect the risk.

The study titled "Association of Body Mass Index and Age With Subsequent Breast Cancer Risk in Premenopausal Women" was published in the journal JAMA Oncology on June 21.

"It is well known that women who gain weight, particularly after menopause, carry an increased risk of postmenopausal breast cancer," said co-senior author Dale Sandler, who is the head of the Epidemiology Branch at the National Institute of Environmental Health Sciences (NIEHS).

"Our finding that breast cancer risk is not increased in obese premenopausal women, and in fact decreases, points to the possibility that different biologic mechanisms are responsible for causing breast cancer in younger women."

After forming the Premenopausal Breast Cancer Collaborative Group, the research team examined data from 19 different studies on 758,592 women from around the world. Using several studies over a single study helped identify patterns, Sandler said, since breast cancer is relatively rare before menopause.

All the women from the studies were categorized into four groups based on age range: 18 to 24, 25 to 34, 35 to 44, and 45 to 54. Each group was then evaluated for their risk of developing breast cancer with regards to their BMI measures. In total, 13,082 women developed breast cancer over the study periods.

The results indicated a 12 to 23 percent reduction in the relative risk of breast cancer before menopause, for each five-unit increase in BMI depending on age. The strongest association seemed to be found in the age group of 18 to 24 years.

"We hope this is the first of many studies to specifically focus on risk factors for breast cancer among young women," said Dr. Katie O'Brien, a staff scientist at the NIEHS one of the authors of the study.

The authors hoped understanding the biological mechanism could potentially lead to cancer prevention treatments in the future. 

Among older women, it is believed fat cells can increase estrogen levels and promote the development of hormone-receptor-positive breast cancers. The exact reason why high BMI seemed to reduce the risk of breast cancer in young, premenopausal women was not found in the new study.

But the researchers cautioned the findings in no way encouraged young women to intentionally gain weight. 

"There are so many health risks associated with being overweight or obese," Sandler said. "We still believe it is important for women to maintain a healthy weight throughout life."