According to results of a new research, even women within a normal weight range may have an increased risk of breast cancer if they have high levels of body fat.
One of the main risk factors for developing breast cancer is being overweight or obese after menopause, this is according to the information provided by the Centers for Disease Control and Prevention (CDC).
However, recent evidence suggests that excessive weight may not be the only element of risk to consider. A study whose discoveries were presented at this month’s American Association for Cancer Research Special Conference, titled Obesity and Cancer: Mechanisms Underlying Etiology and Outcomes, highlights body fat as an independent risk factor, even in the perspective of a normal body mass index (BMI).
Study author Dr. Neil Iyengar, from the Memorial Sloan Kettering Cancer Center in New York City, NY, explains;
“It was previously unknown whether individuals who have a normal BMI but increased body fat have an increased risk of developing cancer.”
“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.”
The link between body fat and the risk for invasive breast cancer has not been addressed by research so far since it is hard to calculate how much of a person’s BMI is taken up by fat, and how much by bones and muscles.
“Body fat levels are typically measured via BMI, which is a ratio of weight to height. While BMI may be a convenient method to estimate body fat, it is not an exact way to determine whole body fat levels, as muscle mass and bone density cannot be distinguished from fat mass,” says study co-author Prof. Thomas Rohan, from the Albert Einstein College of Medicine in New York City, NY.
To overcome this difficulty, the researchers used a technique that permits specialists to measure different elements of body composition, called dual-energy X-ray absorptiometry (DXA). This separate the levels of body fat more precisely from other masses that affect weight.
Dr. Iyengar and colleagues sourced their data from the Women’s Health Initiative, a long-term observational study focused around postmenopausal women aged 50 to 79.
From the current research, the team examined the data of participants with a normal BMI — from 18.5 to approximately 25 — and who had no previous diagnosis of breast cancer, also taking into consideration basic DXA measurements. These amounted to a total number of 3,460 participants. The median follow-up period for the participants was of about 16 years.
During the follow-up period, the participants were monitored for invasive breast cancer; where a cancer diagnosis was given, the women were then further assessed for estrogen receptor positivity, referring to types of cancer in which the malignant cells’ growth is aided by exposure to estrogen.
By the end of the study, of all the participants they monitored, 182 had developed invasive breast cancer during the follow-up period, and 146 of these showed estrogen receptor positivity.
When analyzing the data, the scientists discovered that the women with a normal BMI but a high whole body fat mass had almost twice the risk of estrogen receptor-positive breast cancer, compared with those with a normal BMI but low levels of whole body fat mass.
The team also noted that the risk was heightened by 35 percent for each 5-kilogram growth in body fat, even as the BMI remained within normal limits.
“It is also notable that the level of physical activity was lower in women with higher amounts of body fat,” Dr. Iyengar points out, which “suggests that physical activity may be important even for those who are not obese or overweight.”
The scientists stressed the fact that their results may stun healthcare practitioners, but they will with any luck allow for better risk assessment in the future, which should lead to more effective use of preventive strategies.
“These findings will probably be surprising to many doctors and patients alike, as BMI is the current standard method to assess the risks for diseases related to body weight,” says.
Dr. Andrew Dannenberg, from the Sandra and Edward Meyer Cancer Center of Weill Cornell Medicine in New York City, NY said the outcome of the research will alert women of the likelihood of increased risk of breast cancer related to body fat, irrespective of a healthy weight.