A Piece of the Puzzle: Physical Activity and Breast Cancer
In 2026, there are projected to be 2,114,850 new cancer cases and 626,140 cancer deaths in the United States, making it the second leading cause of death.
For women, nearly one third of projected new cancer diagnoses arise from breast cancer alone.
Evidence suggests that physical activity can help mitigate or prevent breast cancer. One study found that physical activity lowers breast cancer risk by 25% relative to inactivity. However, the underlying mechanism remains unknown.
One theory is that physical activity lowers concentrations of the hormones that make the cancer more aggressive. In a recent study, researchers investigate this for postmenopausal women with hormone receptor-positive breast cancer.
Hormones, Physical Activity, and Breast Cancer
About 70-80% of newly diagnosed breast cancers are hormone receptor-positive, meaning the cancerous tumor has receptors for certain hormones which stimulate cancerous cell growth.
Relatedly, lowering the concentrations of those hormones can stymie the cancer.
One key group of hormones for breast cancer are estrogens. These are sex hormones, important in sexual and reproductive health. The main estrogens are:
- Estradiol (primary form during reproductive life)
- Estriol (primary form during pregnancy)
- Estrone (primary form after menopause)
Studies have found that increased physical activity is associated with lower estrogen concentrations. However, research often focuses on the concentration of all estrogens, or of estradiol specifically. Fewer focus on the concentration of estrone, leaving a gap in breast cancer research for postmenopausal women.
This study helps fill that gap, focusing on postmenopausal women and separating out the effect of physical activity on estrone specifically.
Estrone and Physical Activity Are Intertwined
The authors of this study analyze data from postmenopausal women with previous diagnoses of hormone receptor-positive breast cancer.
For each of the relevant hormones, the authors calculate whether the concentration appears to increase, decrease, or remain unaffected by physical activity. Plasma estrone concentration was measured using the Arbor Assays Estrone ELISA Kit.
The only significantly affected hormone was estrone, which appears to decrease with increased physical activity.
The Catch: BMI
The study suggests that estrone is the key hormone reduced by physical activity in this population, but with one caveat.
In addition to hormone levels, the authors measured the BMI (Body Mass Index) of the enrolled women. The authors discovered that BMI is also significantly positively correlated with estrone levels.
This is important because individuals who exercise more tend to have lower body mass and therefore a lower BMI.
To ensure that the observed effect of physical activity on estrone levels was a direct effect and not simply a byproduct of having a lower BMI, the authors computed the variance inflation factor (VIF) for physical activity and BMI. This is a number indicating whether their significance is artificially inflated due to their correlation. A VIF of one indicates no artificial inflation; a VIF above five is cause to reevaluate the correlation. The computed VIF for both physical activity and BMI was 1.073, indicating that physical activity lowered estrone concentrations independent of its association with BMI.
In Conclusion
Evidence suggests that physical activity can reduce the risk of breast cancer. This study supports the theory that, in postmenopausal women with hormone receptor-positive breast cancer, the reduction in risk is due to physical activity lowering concentrations of plasma estrone.
To see how our kits are being used in other oncology research, be sure to check out our publications page!
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Author: Havi Ellers
Edited by: Charukesi Sivakumar
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