Women with a normal BMI can no longer tick off weight as breast cancer risk factor, US researchers say.

According to their study, published in JAMA Oncology, it’s body fat that increases the risk even if the woman falls into a healthy weight range.

The study was in fact a secondary analysis of the Women’s Health Initiative clinical trial along with observational study cohorts involving almost 3500 post-menopausal, healthy BMI women who at baseline had their body fat analysed (by DXA) and were then followed up for a median duration of 16 years.

What the researchers discovered was that women in the highest quartile for total body fat and trunk fat mass were about twice as likely to develop ER-positive breast cancer.

“In this long-term prospective study of postmenopausal with normal BMI, relatively high body fat levels were associated with an elevated risk of invasive breast cancers,” the study authors spelled.

Perhaps less surprisingly, the analysis also found that the breast cancer risk increased incrementally as the body fat levels increased.