A new study suggests that breast cancer survivors who carry a genetic predisposition to obesity face a higher risk of early death compared with survivors without that genetic risk — but there’s good news: a simple daily habit like walking can help offset that danger.
“Genetics are not destiny,” says Clara Bodelon, PhD, senior principal scientist at the American Cancer Society and lead author of the study. “There are ways to reduce the impact of genetic risk on mortality by adding more steps to your day.”
Genetic Risk and Breast Cancer Survival
Previous research has shown that obesity or being overweight increases the risk of mortality in breast cancer patients. This study, however, focused specifically on whether a genetic tendency toward higher body weight influences survival among breast cancer survivors.
Researchers analyzed data from more than 4,000 postmenopausal women in their 60s and 70s who were diagnosed with a first, nonmetastatic breast cancer between 1992 and 2017. Participants were part of the American Cancer Society’s Cancer Prevention Study II Nutrition Cohort and were followed for nearly 15 years on average.
To estimate genetic risk for higher body weight, researchers calculated a polygenic score for body mass index (BMI) by combining the small effects of more than 900 genetic markers linked to obesity. Based on this score, women were grouped into high, medium, or low genetic risk categories.
The study found that women with high genetic risk were more likely to have obesity at diagnosis. However, genetics did not entirely determine body size: more than 40% of women in the high-risk group had a healthy BMI, while about 12% of women in the low-risk group were obese.
“Genes play a role, but lifestyle choices are equally important,” says Azka Ali, MD, a breast medical oncologist at Cleveland Clinic who was not involved in the study.
Higher Genetic Risk Tied to Increased Mortality
The analysis revealed that breast cancer survivors with a high genetic risk for obesity had a 15% higher risk of death from any cause compared with those with low genetic risk. The most common causes of death were breast cancer itself and heart disease.
Walking Can Offset Genetic Risk
The study also examined physical activity, focusing on walking, which is known to improve metabolism, reduce inflammation, and lower heart disease risk. Researchers found:
Walking more hours per week was associated with lower mortality across all levels of genetic risk.
Participants who walked four or more hours weekly had a roughly 25% lower risk of early death than those walking less than one hour per week.
Survivors with high genetic risk could reduce their mortality risk to levels similar to low-risk women by adding about 15 extra minutes of walking per day — roughly 1,200 to 1,500 steps.
“This is encouraging evidence that healthy lifestyle choices can mitigate genetic risk,” says Dr. Ali.
Practical Tips
Even a short daily walk — a stroll around the block, taking stairs, or parking further from stores — can have measurable benefits for breast cancer survivors, regardless of weight or genetic predisposition.
Dr. Bodelon emphasizes that, while losing weight can be challenging for postmenopausal women, even small increases in daily activity can substantially lower risk.
Limitations
As an observational study, the research cannot prove causation. Physical activity was self-reported, and participants were primarily white postmenopausal women of European ancestry, which may limit generalizability.
Nonetheless, the findings underscore a hopeful message: small, consistent lifestyle changes, such as walking 15 extra minutes a day, can meaningfully improve survival outcomes for breast cancer survivors — even for those with a genetic predisposition to obesity.
