A new study shows that postmenopausal women with higher levels of body fat have an increased risk of developing invasive breast cancer, even if they are within a normal BMI range.

The study, presented at the American Association for Cancer Research Special Conference in January 2018, is the first to look at the correlation between body fat and cancer. BMI is the current standard to assess risk for diseases associated with body weight but it can be difficult to calculate how much of a person’s BMI is made up of fat and how much by muscles and bones.

In this study, researchers used dual-energy X-ray absorptiometry (DXA) to conduct scans of the participants. DXA is commonly used to measure bone density but it can also be used to specifically measure fat to more accurately differentiate total body fat levels from other masses that affect weight.

The study analyzed data from 3,460 women involved in the Women’s Health Initiative (WHI), a larger study following the health of post-menopausal women, aged 50 to 79. The women were all within normal BMI levels at the start of the study and had no history of breast cancer.

Over 16 years, 182 women developed breast cancer and 146 of these had tumours that were estrogen receptive (ER) positive, meaning estrogen contributed to their growth.

Women with a normal BMI but high body fat level were almost twice as likely to develop ER-positive breast cancer, compared with those who had a normal BMI and low levels of body fat. The risk increased by 35% for each 5-kg jump in body fat, even if BMI was normal.

“It was previously unknown whether individuals who have a normal BMI but increased body fat have an increased risk of developing cancer,” explains Dr. Neil Iyengar, study author and medical oncologist at Memorial Sloan Kettering Cancer Center in New York. “Our findings show that the risk of invasive breast cancer is increased in postmenopausal women with normal BMI and higher levels of body fat, meaning that a large proportion of the population has an unrecognized risk of developing cancer.”


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