Postmenopausal women who are overweight or obese are at increased risk of invasive breast cancer compared to normal-weight postmenopausal women.

The risk increased with increasing BMI (body mass index). Disappointingly, losing weight had no effect on the risk.

The analysis of follow-up data from the US Women’s Health Initiative clinical trials shows women with a BMI of 35 or greater have a 58% higher risk of invasive breast cancer than those of normal weight.

Also of note, women with a healthy BMI of less than 25 at the start of the study who gained more than 5% bodyweight over the follow-up period, had an increased risk of breast cancer.

The risk does not vary with the use of HRT, according to a research report in JAMA Oncology.

“This challenges the simple suggestion that patients who are overweight or obese should just lose weight to reduce their cancer risk,” write Dr Clifford Hudis and Dr Andrew Dannenberg in an accompanying editorial.

“Weight control may be very effective for many weight-associated illnesses and ailments, but the data suggesting that it will reduce an already elevated risk of breast cancer are limited.”

The authors say this research is a call to action on several fronts, including refining the understanding of why overweight and obesity raises the risks of some cancers.

The Women’s Health Initiative included 67,142 postmenopausal women enrolled from 1993 to 1998 with a median of 13 years of follow-up. There were 3,388 invasive breast cancers.

Amanda Davey

Last Reviewed: 15/06/2015

Reproduced with kind permission from


Obesity Associated with Increased Breast Cancer Risk in Postmenopausal Women: JAMA Oncology