Findings of a new study have found that older women with higher body fat levels may have elevated risk of breast cancer regardless that their weight is normal.

BMI

Earlier studies have found that women who are obese or overweight are at greater risk of breast cancer after menopause. For a long time, though, doctors used the body mass index or BMI as a gauge if a person has a normal weight.

The problem with BMI is that it cannot tell the difference between fat, muscles, and bones, so it is not an accurate gauge of body composition. The findings of the new study showed that BMI can neither predict a person's risks of breast cancer.

For the study presented at the American Association for Cancer Research conference in Austin, Texas on Friday, Neil Iyengar from Memorial Sloan Kettering Cancer Center and colleagues looked at the data of more than 3,400 women between 50 and 79 years old, all of whom had normal BMI at baseline.

Over the course of 16 years, some of the women developed breast cancer. In most cases, the tumors were estrogen receptor-positive, which means that estrogen fuels the growth of the tumor.

Body Fat Linked To Higher Odds Of ER-Positive Breast Cancer

Researchers found that women with more fat had increased odds of developing ER-positive breast cancer. Those whose fat levels are in the top 25 percent had twice the risk of developing this type of cancer compared with their counterparts in the bottom 25 percent.

The researchers said that the findings do not provide a definite proof that body fat causes cancer. However, it appears to be a risk factor even after accounting for lifestyle, use of hormone therapy, and family history of breast cancer.

Why Body Fat Matters

Researchers explained that body fat matters because it is an active issue. Once it accumulates in excess, it can outgrow its blood supplies and fat cells die. This can eventually lead to inflammation and the production of the so-called growth factors that support cancers. Fat cells also produce estrogen.

Iyengar and colleagues said the findings suggest that women should not just concentrate on their weight but also on their body fat levels.

"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," Iyengar said.