Postmenopausal women with a normal Body Mass Index (BMI) who have higher body fat levels have an increased risk of developing Breast Cancer, raising questions about the link between cancer and obesity. This has been supported by data which was presented by the American Association for Cancer Research Special Conference Obesity and Cancer: Mechanisms Underlying Etiology and Outcomes (Jan 27-30).

CANCER RISK
Neil Lyengar (MD), medical oncologist at Memorial Sloan Kettering Cancer Center outlines that it was previously unknown if those with normal BMI but high body fat levels are at an increased risk of developing cancer. Iyengar’s study finds that the risk of developing invasive Breast Cancer is increased in postmenopausal women with normal BMI and higher levels of body fat, which means that a significant number of the population have an unrecognised risk of developing cancer.

BMI is a ratio of weight to height. While BMI may be a good approach to estimate body fat, it may be an inappropriate method to convey exact weight as muscle and bone mass cannot be distinguished from fat mass, mentioned by Thomas Rohan, MBBS, PHD, DHSc, professor and chair, Department of Epidemiology and Population Health at Albert Einstein College of Medicine A specific way of measuring fat content can be procured with a Dual energy X-ray absorptiometry (DXA), which results in a valid assessment of exact body fat, he explained.

Researchers assessed data from the Women’s Health Initiative (WHI), a study which looks into the health of postmenopausal women who are aged 50-79. The participants of the study included women who had a normal BMI (18.5-<25.0) with baseline DXA measurements and no record of having Breast Cancer.

FINDINGS AND OUTCOMES
During a 16 year timeframe, participants were frequently assessed for the development of invasive Breast Cancer and cancer cases faced evaluation for estrogen receptor (ER) positivity. 3,460 participants were involved in the study, of which, 182 developed invasive Breast Cancer; 146 cases were ER-positive.

The lowest quartile of whole body fat mass was compared with the highest quartile. The comparison revealed that those in the highest quartile were two times more at risk for ER-positive Breast Cancer, meaning there is an obesity cancer risk.

Another finding by Lyengar and his team was that the risk of ER-positive Breast Cancer increased by 35 percent per each 5kg increase in whole body fat, despite the participants having a normal BMI. Lyengar observed that physical activity was lower in women with higher levels of body fat, suggesting that physical activity is important in sustaining good health for those who are not obese or overweight.

Andrew Dannenberg, MD and associate director of Cancer Prevention at the Sandra and Edward Meyer Cancer Center of Weill Cornell Medicine mentions “The findings of this study will surprise many patients and doctors, as BMI is the current method used to assess risks for diseases that are associated with obesity”. Dannenberg hopes the findings from the study will alert women to the possibility of developing cancer as a result of high body fat, despite having a normal and healthy weight.

One limitation of the study was that it was unable to analyse the risk of cancer developing over time as body fat increases. In addition, this study may only be generalised to postmenopausal women and not other populations.

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