Three hundred minutes of moderate exercise a week can help prevent cancer

More than 46,000 cases of cancer could be prevented annually in the United States if nearly all Americans walked about 45 minutes a day, revealed a revealing new study on inactivity, exercise and malignant tumors.

The study, which looked at the cancer incidence and physical activity habits of nearly 600,000 American men and women across all states and the District of Columbia, found that about 3% of the most common cancers in the US are strongly linked to physical inactivity. . The findings indicate that something as simple as getting up and moving could help tens of thousands of us avoid getting cancer for years to come.

We already have plenty of evidence that exercise affects cancer risk. In past experiments, physical activity has modified the immune system in ways that support the body’s ability to fight tumor growth. Exercise can, for example, intensify the activity of certain immune cells that are known to fight cancer cells. Exercise is also associated with the prolonged survival of people with certain types of cancer, possibly because it boosts levels of inflammatory substances that inhibit the growth of cancer cells. A 2016 article published in JAMA Internal Medicine concluded that the risk of having at least 13 types of cancer, including breast, bladder, blood and rectum, drops sharply if a person is physically active. A separate report from 2019 estimated that these reductions could reach 69%.

So for the new study, published in October in Medicine & Science in Sports & Exercise, researchers at the American Cancer Society and Emory University in Atlanta employed a type of sophisticated statistical analysis called PAF to measure the links between cancer and physical inactivity. PAF stands for “population attributable risk”. It’s a mathematical way for scientists to estimate how many occurrences of a disease — or responses to a drug or other biological reactions — in a larger population appear to be the result of a particular behavior or other factor. It can essentially tell us how many annual cases of colon cancer, say out of all known annual cases of the disease, can reasonably be attributed to smoking, drinking alcohol, eating fatty foods, or spending too much time sitting.

To begin calculating the cancer PAF resulting from inactivity, American Cancer Society scientists began by collecting anonymized data from the US Cancer Statistics database on national and state-level cancer cases for all 20-year-old Americans. years or more between 2013 and 2016. The team focused on both total cancer cases and the seven cancers that past studies have linked closely in part to physical activity (or lack thereof) — that is, stomach tumors, kidneys, esophagus, colon, bladder, breast and endometrium.

They then checked the reported physical activity of American adults, based on more than half a million responses to two large federal surveys. Both ask people how they exercise and how often. The researchers collected responses from adults in all states and grouped them based on whether people met the American Cancer Society’s recommendations on physical activity. These guidelines ideally ask people to get 300 minutes (five hours) a week of moderate exercise, such as brisk walking, to reduce their risk of cancer.

To conclude, the researchers adjusted these statistics for body mass and other factors, gathered additional data on cancer risks, and fitted all these numbers into an equation, which gave them the population-attributable risk of cancers linked to sedentary lifestyles. This number turned out to be 46,356, or about 3% of annual cancers (excluding non-melanoma skin cancers).

When they then looked at individual types of cancer, they found that stomach cancer is the most linked to inactivity: about 17% of annual cases can be attributed to lack of exercise, compared to 4% of bladder cancers. The numbers also varied from state to state, reaching nearly 4% of cancers in many southern US states, where residents tend to report that they get relatively little exercise, but only 2% in much of Colorado, Idaho, Utah, Wyoming, Montana and Nevada, where the population is relatively active.

But the good news is that these numbers are malleable. We have the possibility to reduce them. Physical exercise “has the potential to prevent many cancers in the United States,” said Adair K. Minihan of the American Cancer Society and leader of the new study. According to her, if everyone in America who is able to exercise began to walk for an hour on weekdays, theoretically the 46,356 cases of cancer linked to sedentary lifestyles would disappear.

Of course, cancer is a highly complex disease that has many intertwined and overlapping causes, with sedentary lifestyle playing only a small potential role. Furthermore, statistical risks never drop to zero. Many of the most active people can develop cancer and do, Minihan said.

She pointed out that the study is not intended to make people feel ashamed of not being physically active, nor to suggest that someone’s tumor is their fault for missing the gym every now and then. “There are so many obstacles” to exercising, she said, and many factors that contribute to determining who eventually develops cancer. But the results do indicate that if each of us could just include in our routine about 45 minutes of simple exercise, like walking, into our routine, we could transform our risk of developing many types of malignant tumors.

_{Translation by Clara Allain}