Breast cancer: Less sitting, more physical activity may lower risk

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• Researchers analyzed the link between breast cancer and physical activity as well as time spent sitting.
• They found that higher levels of physical activity and less sedentary time reduce breast cancer risk.
• They concluded that a greater focus on promoting active lifestyles would likely reduce breast cancer risk.

Physical activity and less sedentary time have been linked to a lower risk for breast cancer in observational studies.

While researchTrusted Source suggests a generally consistent link between breast cancer risk and physical activity, the linkTrusted Source between sedentary time and breast cancer risk is less clear and less well-studied.

Most studies investigating the link between breast cancer and physical activity or sedentary time have been observational in nature. This means that rather than providing a causal link, they provide a correlation that may be subject to biases.

Recently, researchers analyzed healthcare data from 76 studies to determine whether there is a causal link between activity levels and breast cancer.

They found that greater levels of physical activity and less sedentary time likely reduce breast cancer risk.

“The findings of this new study lend further support for current recommendations to be physically active for health, including lowering breast cancer risk,” said Dr. I-Min Lee, professor of medicine at Harvard Medical School, who was not involved in the study, in conversation with Medical News Today.

“Even modest increases in physical activity at the population level will decrease the number of new breast cancer diagnoses made each year,” Dr. Brigid Lynch, deputy head of the Cancer Epidemiology Division at Cancer Council Victoria, Australia, one of the study’s authors, told MNT.

How sitting time correlates to cancer risk

For the study, the researchers analyzed data from 130,957 women of European ancestry from the Breast Cancer Association Consortium (BCAC).

Altogether 69,838 women had invasive breast cancer tumors—those that had spread locally, 6,667 had in-situ tumors that had not spread, and 54,452 did not have breast cancer and were included in the study as controls, for comparison.

The researchers used a statistical method known as Mendelian randomization to assess the relationship between cancer risk and type, and genetic factors linked to physical activity and sedentary behavior.

The researchers found that higher levels of genetically predicted physical activity were linked to a 41% lower risk of invasive breast cancer independent of menopausal status, tumor type, stage, or grade.

They also found that women with genetically predicted vigorous physical activity on three or more days of the week had a 38% lower risk of pre and perimenopausal breast cancer—but not postmenopausal risk—than those who self-reported no vigorous physical activity.

The researchers also found that genetic variants that predisposed women to greater amounts of sitting time were linked to a 104% higher risk of triple-negative break cancer in hormone-negative tumor types.

They noted, however, that evidence linking sedentary behavior to increased breast cancer risk overall was weak.

Being active, hormones, and cancer

When asked how a less sedentary lifestyle may reduce breast cancer risk, Dr. Lee said: “High physical activity and low sedentary time can decrease breast cancer risk by decreasing adiposity [fatty tissue in the body], beneficially influencing sex hormone levels, improving metabolic dysfunction, and decreasing inflammation.”

“The main way that physical activity reduces breast cancer risk is by lowering the levels of sex steroid hormones – lower levels of estrogens and androgens are related to a lower risk of breast cancer.”
— Dr. Brigid Lynch

“There has been less certainty about the role of sitting time—observational studies have produced conflicting findings, but this Mendelian randomization study suggests that long periods of sitting increase breast cancer risk. Our research findings warrant a stronger cancer control focus on increasing physical activity and reducing sedentary behavior,” Dr. Lynch added.