A new study from Spain suggests that almost 40% of hormone-positive breast cancer cases in postmenopausal women could be linked to excess body fat.
This is much higher than the current estimate, which attributes only about 10% of these cancers to excess weight, based on a commonly used measure called Body Mass Index (BMI).
The researchers believe that the real impact of obesity on breast cancer has been underestimated, and they suggest that a more accurate method of measuring body fat may give a clearer picture of the risk.
BMI is a widely known tool used to classify weight based on a person’s height and weight. However, it doesn’t take into account factors like age, gender, or ethnicity. As people age, particularly women, BMI might not provide an accurate reflection of their body fat.
Recognizing this, the researchers compared BMI with a more specific measure called the Clínica Universidad de Navarra–Body Adiposity Estimator (CUN-BAE), which does consider both age and gender, in over 2,000 postmenopausal women.
Half of these women had breast cancer, while the others did not. The two groups were matched by age, gender, and region to ensure fairness in comparison.
This study is part of a larger project called MCC-Spain, which is looking into the environmental and genetic factors that contribute to different cancers, including breast cancer.
Participants in this study answered questions about various factors that could affect their cancer risk, such as their lifestyle, medical history, and reproductive history.
The researchers also collected detailed information on the women’s diets and alcohol consumption between the ages of 30 and 40, as this can influence cancer risk.
The CUN-BAE method groups body fat percentages into four categories: less than 35%, between 35% and 39.9%, between 40% and 44.9%, and 45% or higher.
In comparison, BMI classifies weight into categories based on numbers: under 25 is considered normal weight, 25–29.9 is considered overweight, and 30 or above indicates obesity.
The study found that the average BMI in women without breast cancer was slightly above 26, while it was a bit over 27 in those with breast cancer.
However, the CUN-BAE measure showed that average body fat was just below 40% in women without cancer and a little over 40% in those with the disease.
Women with a BMI under 25 (considered healthy) made up 45% of the group without breast cancer but only 37% of the group with breast cancer. As for obesity (BMI of 30 or higher), 20% of the women without breast cancer were obese, compared to just over 24% of those with cancer.
Interestingly, when using the CUN-BAE to measure body fat, 20.5% of women without breast cancer had less than 35% body fat, compared to 16% of women with breast cancer.
However, 46% of women without breast cancer had body fat percentages over 40%, while more than 53% of women with breast cancer were in this category.
Women with body fat percentages over 45% were more than twice as likely to have hormone-positive breast cancer compared to those with less than 35% body fat.
The researchers also found that using BMI alone underestimated the role of excess body fat in breast cancer. When they used BMI, they estimated that 23% of breast cancer cases were linked to obesity.
But when they used CUN-BAE, this number jumped to 38%. In cases of hormone-positive breast cancer, which was the focus of this study, the difference was even greater: BMI suggested that 20% of these cancers were linked to obesity, while CUN-BAE showed that 42% could be attributed to excess body fat.
Although the researchers acknowledge that this study can’t prove a direct cause-and-effect relationship between obesity and breast cancer, the results still highlight the importance of using more accurate methods to measure body fat.
The CUN-BAE formula used in this study was based on a group of mostly inactive people, which could limit the findings. Still, the study’s conclusion is clear: excess body fat is a significant risk factor for hormone-positive breast cancer in postmenopausal women.
Relying only on BMI might underestimate the true impact of obesity, making it harder to plan effective prevention programs.
These findings could help public health officials improve breast cancer prevention efforts, especially in postmenopausal women, by promoting more accurate ways to measure body fat and better assess cancer risk.
If you care about breast cancer, please read studies about how eating patterns help ward off breast cancer, and soy and plant compounds may prevent breast cancer recurrence.
For more health information, please see recent studies about how your grocery list can help guard against caner, and a simple way to fight aging and cancer.
The research findings can be found in the Journal of Epidemiology and Community Health.
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