New data presented at the American Association for Cancer Research’s ‘Obesity and Cancer’ Conference has suggested that having higher levels of body fat can increase the risk of breast cancer in post-menopausal women who have a normal body mass index (BMI).

Monday 29 January 2018      Latest research

Researchers from the Memorial Sloan Kettering Cancer Center analysed data from the Women's Health Initiative (WHI), an observational study following the health of postmenopausal women ages 50-79, and used readings from dual energy X-ray absorptiometry (DXA) technology that can specifically measure for fat content, resulting in a more accurate assessment of patients’ total body fat levels. The study included participants who had a normal BMI (between 18.5 to <25.0) with baseline DXA measurements and no history of breast cancer.

Of the 3,460 participants in the study, 182 developed invasive breast cancer during the median 16 years of follow-up – with 146 of these cases being ER-positive. In multivariable analysis, women in the highest quartile of whole body fat mass had approximately a doubling in their risk of developing ER-positive breast cancer compared to those in the lowest quartile.

The scientists also found that the risk of ER-positive breast cancer increased by 35 percent for each 5-kilogram increase in whole body fat, despite having a normal BMI. However, a limitation to the study is that the researchers were unable to analyse how changes in body fat over time related to breast cancer risk.

Dr Tom Beattie, Health Information Officer at Breast Cancer Now, said:
“This interesting study reinforces that having a bigger waist size may increase your risk of breast cancer, even if your BMI is within a healthy range. But crucially it also supports existing evidence that keeping physically active can reduce your breast cancer risk in other ways that are not actually linked to losing weight, which we hope will help many more women lower their chances of developing the disease.

“We know that the more fat tissue you have around your body, the higher your levels of oestrogen are likely to be, which can increase your risk of breast cancer. Our BMI and waist size are a very good proxy for estimating our body fat and its impact on our breast cancer risk – and it’s important to know that a waist size over 31.5 inches is considered to be high and may increase your risk of breast cancer, even with a healthy BMI.

“While we cannot change some things that affect our risk, such as getting older, there are some things we can do something about. We’d encourage all women to keep physically active, to try to maintain a healthy weight and to reduce their alcohol intake to help keep their breast cancer risk as low as possible.”