Excess body fat significantly increases the risk of postmenopausal breast cancer
Excess body fat emerges as a potent contributor to postmenopausal breast cancer risk, with startling findings suggesting that around 40% of hormone receptor-positive cases in postmenopausal women may be tied directly to surplus body fat. This research, recently published in the Journal of Epidemiology & Community Health, challenges earlier assumptions that linked just one in ten such cases to excessive weight, typically assessed using body mass index (BMI). The disparity highlights a critical issue: BMI, the ubiquitous metric of body fat, may drastically underrepresent obesity’s true impact on cancer risk, especially in postmenopausal populations.
Researchers underscore BMI’s limitations, pointing out that it neglects variables like age, sex, and ethnicity, all of which shape body composition distinctively. In contrast, the study employed the ClĂnica Universidad de Navarra–Body Adiposity Estimator (CUN-BAE)—a validated and nuanced measure that accounts for both age and sex. Examining 1,033 White postmenopausal women diagnosed with breast cancer and 1,143 matched controls free of the disease, the research team used this tool to reveal critical distinctions between the two groups.
Participants, part of the extensive MCC-Spain study, were evaluated for numerous potential risk factors, ranging from sociodemographic and lifestyle elements to personal and familial medical histories. Additionally, detailed dietary data were captured through a semi-structured, 140-item Food Frequency Questionnaire, and alcohol consumption patterns were reported for the ages of 30 to 40.
The CUN-BAE metric stratifies body fat into four categories: under 35%, 35–39.9%, 40–44.9%, and 45% and higher. Meanwhile, BMI segments weight as follows: under 25 kg/m², 25–29.9, 30–34.9, and 35 and higher. Among the comparison group, average BMI stood slightly above 26, while in the breast cancer group, it surpassed 27. The average CUN-BAE was close to 40% for the controls and rose marginally above 40.5% for the cancer group.
Breaking down the findings further, 45% of the comparison group maintained a BMI below 25, a reference mark, compared to only 37% among those with breast cancer. Obesity, marked by a BMI of 30 or more, appeared in 20% of the comparison group versus just over 24% in the breast cancer group. When measured with CUN-BAE, only 20.5% of the comparison group had body fat levels below 35%, compared to 16% of the cancer group. Notably, CUN-BAE measurements of 40% or higher were present in over 46% of the comparison group and rose to 53% among breast cancer patients.
Strikingly, a CUN-BAE score of 45% or more correlated with more than a twofold increase in postmenopausal breast cancer risk compared to a score below 35%. This pattern sharply contrasts with BMI measurements, which showed no such correlation. This discrepancy led researchers to propose that, while BMI calculations attributed 23% of breast cancer cases to excess body fat, CUN-BAE estimates elevated that figure to 38%. The gap widened further when isolating hormone receptor-positive cases (680 instances): here, BMI assigned only 20% of the risk to excess fat, while CUN-BAE estimated a dramatic 42%.
The case-control nature of this study precludes establishing causality, researchers caution. They also acknowledge that the CUN-BAE formula is based on a sedentary sample, and the number of hormone-negative cases in the study was limited. Still, their conclusions are bold: “Our study indicates that excess body fat is a significant risk factor for hormone receptor-positive breast cancer in postmenopausal women. These findings suggest that BMI-based assessments might undervalue the cancer risk posed by obesity. For accurate cancer burden estimates, more sophisticated fat measures like CUN-BAE should be prioritized, particularly in the context of postmenopausal breast cancer.”
Source: BMJ Group