Study: Increasing physical activity, reducing sitting time may decrease breast cancer risk

Key takeaways

• Researchers used Mendelian randomization to obtain genetic evidence supporting a causal relationship between activity level and breast cancer risk.
• Vigorous activity was linked to a 38% lower breast cancer risk, while higher levels of genetically predicted sitting time were associated with a 104% increased risk for triple-negative breast cancer.
• The study adds to existing evidence that suggests reducing sedentary time and boosting physical activity may lower the incidence of future breast cancer rates.

Staying active and spending less time sitting are highly likely to reduce breast cancer risk, according to researchers.

Physical activity has been shown to reduce the risk for cancer. In addition, observational studies have previously linked sedentary behavior to a higher breast cancer risk, but proving that it causes cancer is quite different, Suzanne C. Dixon-Suen, a postdoctoral research fellow at Deakin University in Australia, and colleagues wrote. So, they conducted a Mendelian randomization study, which simulates randomized trial groups using genetic variants in place of risk factors, in an attempt to assess causality.

The findings, published in the British Journal of Sports Medicine, revealed that, overall, higher genetically predicted physical activity was associated with a 41% lower risk for invasive breast cancer, regardless of menopausal status or tumor characteristics.

“Our study provides strong evidence that greater overall physical activity, greater vigorous activity, and lower sedentary time are likely to reduce breast cancer risk,” Dixon-Suen and colleagues wrote, noting that a “more widespread adoption of active lifestyles may reduce the burden from the most common cancer in women.

The researchers analyzed data from 130,957 women of European ancestry, 54,452 of whom did not have breast cancer. Of those with cancer, 6,667 had tumors that had not yet spread (in situ) and 69,838 had invasive tumors.

The researchers then assessed data from previous studies that examined potential genetic explanations for predispositions to physical activity, vigorous physical activity or sedentary time — measured by wearable technology — to genetically predict how active or inactive their study participants were, according to a press release. They approximated the overall breast cancer risk based on whether the participant had gone through menopause, and the risk by cancer type, stage, and grade.

Dixon-Suen and colleagues reported that higher genetically predicted activity levels were linked to a lower risk for breast cancer (OR = 0.59; 95% CI, 0.42-0.83), “with no clearly deferential effects by menopausal status, molecular subtype, morphology, stage or grade.” Vigorous activity was linked to a 38% lower breast cancer risk, according to the release, while higher levels of genetically predicted sitting time were linked to a 104% increased risk for triple-negative breast cancer.

“Short bouts of intense activity may be more protective than equivalent energy expenditure accumulated from light activity,” Dixon-Suen and colleagues wrote. “We found that self-reported vigorous activity was associated with lower pre/perimenopausal breast cancer risk and found weak evidence for a protective effect of vigorous activity overall.”

The researchers wrote that their findings “must be considered in light of biological plausibility.”

“A reasonable body of mechanistic evidence supports numerous causal pathways between physical activity and breast cancer risk,” they wrote. “Pathways involving adiposity, metabolic dysfunction, sex hormones and inflammation have been most thoroughly described. Mechanisms linking sedentary time and cancer are likely to at least partially overlap with those underpinning the physical activity relationship.”

The study supports the idea that reducing sedentary time and boosting physical activity are “likely to lower the incidence of future breast cancer rates,” Dixon-Suen and colleagues wrote.

“A stronger cancer-control focus on physical activity and sedentary time as modifiable cancer risk factors is warranted, given the heavy burden of disease attributed to the most common cancer in women,” they concluded.

References:

• Boosting physical activity/curbing sitting time highly likely to lower breast cancer risk. https://www.eurekalert.org/news-releases/963519. Published Sept. 6, 2022. Accessed Sept. 8, 2022.
• Dixon-Suen SC, et al. Br J Sports Med. 2022;doi:10.1136/bjsports-2022-105132.