How Moving More and Sitting Less May Help Lower Breast Cancer Risk

New research adds further evidence to the link between increased physical activity and lower risk of breast cancer.

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Increasing physical activity and reducing time spent sitting is "highly likely" to help lower breast cancer risk, new research shows, leading experts to further recommend exercise as a preventive measure for the disease.

The new study, published in the British Journal of Sports Medicine, adds evidence to the claim that certain behavioral changes—in this case, more physical activity overall, more vigorous activity, and less sitting time—are helpful in lowering breast cancer risk.

While previous observational studies have shown a link between physical inactivity and sedentary time to an increased risk of breast cancer, it's been more difficult to prove they directly cause breast cancer.

This research aimed to do that through a technique called Mendelian randomization, which can help scientists draw more specific conclusions than observational studies. The technique uses genetic data as a proxy for particular risk factors to examine their causal effect on disease. In this case, exercise genes—or the genetic predisposition to be sedentary or active—were evaluated to see physical activity's effects on breast cancer risk.

The new findings suggest that the impact exercise can have on breast cancer risk may be even stronger than what's previously been reported in observational studies, according to the researchers.

"This Mendelian randomization study confirms that the findings from observational studies are robust, and that there is a causal relationship between physical activity and a reduced risk of breast cancer," study author Brigid Lynch, PhD, a cancer epidemiologist and deputy head of the Cancer Epidemiology Division at Cancer Council Victoria in Australia, told Health.

Physical Activity's Effect on Breast Cancer Risk

For the study, a team of international researchers from Australia, the U.K., and the U.S., examined data from 130,957 women—69,838 women who had invasive breast cancer, 6,667 who had localized tumors, and 54,452 who did not have breast cancer. The data was sourced from 76 different Breast Cancer Association Consortium studies

The researchers also referred to evidence from the U.K. Biobank on how specific genes influence how physically active or inactive different people are. They then used that genetic data as a proxy for physical activity or sedentary behavior.

They calculated the participants' overall breast cancer risk and compared the breast cancer risk in people who were genetically predisposed to exercise frequently and rigorously, to people who were genetically predisposed to be more sedentary.

The researchers found that people who had a genetic predisposition to be more physically active had a 41% lower risk of invasive breast cancer. People who were genetically predicted to vigorously exercise three or more days a week had a 38% lower risk of breast cancer. The team also found that sitting time may ultimately increase the risk of breast cancer by up to 104%, especially for more aggressive types of breast cancer with a poorer prognosis.

"The bottom line is that this study adds further weight to the evidence that physical activity can impact breast cancer risk," Eric Winer, MD, director of the Yale Cancer Center and president of the American Society of Clinical Oncology, told Health.

This isn't the first study to discover a link between physical activity and lowered risk of breast cancer—but using the technique of Mendelian randomization has further strengthened research on the topic.

"All types of studies have their strengths and weaknesses, but when we can use different methods and bring the findings from those different methods together, it really strengthens the evidence," said Lynch.

For a 2019 meta-analysis that reviewed the findings of 10 studies, researchers found that breast cancer survivors who exercised had a 40% lower risk of death from breast cancer compared to people who weren't as physically active.

The same has been found for other types of cancer, too—exercise appears to lower the risk of death in people diagnosed with colorectal cancer and prostate cancer.

It's unclear why exercise has this effect on breast cancer risk, but researchers suspect it may be due to physical activity's ability to lower inflammation in the body and reduce the levels of sex hormones—including estrogens and androgens—that have been linked to a higher breast cancer risk.

The evidence regarding why exercise may be able to reduce a person's cancer risk is still evolving and more research is needed to understand why physical activity appears to lower the risk of breast cancer. "There are a number of theories, but nothing that is conclusive," said Dr. Winer.

How to Further Reduce Your Risk of Breast Cancer

The new study provides more evidence that boosting your physical activity and reducing your sitting time could potentially help prevent breast cancer.

The American Cancer Society recommends getting 150 to 300 minutes of moderate physical activity a week or 75 to 100 minutes of vigorous exercise as this amount of exercise has been linked to a lower cancer risk.

"Physical activity is an important cancer control strategy—we should be doing more to encourage regular physical activity by creating environments that make being active easy," said Lynch.

Dr. Winer also advises postmenopausal women to maintain a healthy weight, as obesity is a known risk factor for breast cancer. Fatty tissue can raise estrogen levels and lead to higher insulin levels, which can contribute to breast cancer. Research also suggests that eating a healthy diet rich in fruits, vegetables and whole grains can help lower your risk of breast cancer.

Avoiding alcohol is also an important part of breast cancer prevention—according to the ACS, even in small amounts, alcohol can increase breast cancer risk. If completely abstaining from alcohol isn't the right choice for you, the ACS suggests no more than one drink a day for women; that amounts to 12 ounces of beer, five ounces of wine, or 1.5 ounces of hard liquor.

For those who have an increased risk of breast cancer—due to a strong family history or an inherited gene mutation—the ACS also suggests genetic counseling, medications to lower breast cancer risk, or even prophylactic surgery to reduce their risk of disease.

In addition to taking preventive measures, it's also crucial to stay up to date with your screenings so healthcare providers can find cancer at earlier stages, when it is easier to treat.

"Although screening does not prevent breast cancer," said Dr. Winer, "following screening recommendations can lower the risk of being diagnosed with a more advanced version of the disease."

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