Cardiorespiratory fitness may reduce breast cancer risk

Key takeaways:

• For postmenopausal women, cardiorespiratory fitness may help protect against breast cancer.
• However, the effects were limited to those with elevated body fat.

Having higher cardiorespiratory fitness may be a protective factor against breast cancer for postmenopausal women with elevated body fat, according to the results of research published in the British Journal of Sports Medicine.

One established risk factor for postmenopausal breast cancer is increased BMI, and previous research has indicated that exercising is linked to a lower risk for breast cancer, particularly in postmenopausal women, Rebecca A. G. Christensen, a PhD student at the University of Toronto Dalla Lana School of Public Health, and colleagues, wrote.

Therefore, physical activity represents a potentially modifiable risk factor.

“Previous research has found that having a higher cardiorespiratory fitness (CRF) can decrease a person’s risk of developing and dying from cardiometabolic conditions, but the relationship between CRF and breast cancer incidence has not been examined,” they wrote.

So, the researchers conducted a prospective cohort study to assess connections between the risk for breast cancer in postmenopausal women and CRF.

“Understanding the relationship between CRF and risk may inform interventions for breast cancer prevention,” Christensen and colleagues wrote.

The researchers used U.K. Biobank data from 17,840 postmenopausal cancer-free women with a CRF assessment. The researchers used Fine and Gray regression to evaluate the association between breast cancer risk and high estimated CRF (eCRF) — categorized as being higher than the 80th percentile within 10-year age bands — accounting for all-cause mortality and non-breast cancer diagnoses as competing risks.

The researchers observed 1,623 cases of non-breast cancer disease, 529 cases of invasive breast cancer and 241 deaths over a median follow-up of 11 years.

Christensen and colleagues found that high eCRF was associated with a 24% lower risk (subdistribution HR [SDHR] = 0.76; 95% CI, 0.6-0.97) for breast cancer, even after adjusting for breast cancer risk factors.

“These findings suggest that participation in sustained physical activity leading to increased CRF may be necessary to significantly lower a woman’s risk of developing breast cancer,” the researchers wrote.

Notably, when stratified by measures of body fat, they found evidence of effect measure modification. In particular, having high eCRF was linked to a lower risk for breast cancer only among those whose percentage of body fat was above the first quintile (SDHR = 0.65; 95% CI, 0.45-0.94) or those who had overweight or obesity (SDHR = 0.33; 95% CI, 0.11-1.01).

“While BMI and percent body fat may still be cofounders of the relationship between eCRF and breast cancer, the fact that the effect estimates were different depending on the category of BMI and percent body fat is also suggestive of effect measure modification,” Christensen and colleagues wrote. “This could be mechanistically explained by the relationship between body fatness, physical activity and eCRF to estrogen and chronic inflammation.”

Christensen and colleagues concluded that their study contributes to understanding of the relationship between interrelated breast cancer risk factors “with the goal of informing preventive interventions.”

“Findings from this study support the notion that physical activity, with the particular goal of increasing CRF, may be beneficial to reduce breast cancer risk in postmenopausal women with an elevated body fat,” they wrote.