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Aerobic exercise may reduce the risk of metastatic cancer by 72 percent, according to new research published in the November 15 issue of Cancer Research. The study is the first to investigate the impact of exercise on the internal organs in which metastases usually develop, like the lungs, liver, and lymph nodes.
The findings suggest that high-intensity aerobic exercise, which derives its energy from sugar, can reduce the risk of metastatic cancer, said research leaders Carmit Levy, PhD, and Yftach Gepner, PhD, in a press release. “If so far the general message to the public has been 'be active, be healthy', now we can explain how aerobic activity can maximize the prevention of the most aggressive and metastatic types of cancer,” the authors said.
The evidence suggesting that higher physical activity levels can lower cancer risk comes mainly from observational studies in which people self-report their activity levels and are followed for years to see if they develop different types of cancer.
According to the National Cancer Institute, there is strong evidence that higher levels of physical activity are linked to lower risk of several types of cancer. Possible reasons for the risk reduction include preventing high blood levels of insulin, reducing inflammation, improving immune system function, and helping to prevent obesity, which is a risk factor for many cancers.
This study included both mice and humans — the mice trained under a strict exercise regimen and healthy human volunteers were examined before and after running.
Human data was also obtained from an epidemiological study that monitored 2,734 people for 20 years — during that time, 243 new cancer cases were recorded. Researchers found that there was 72 percent less metastatic cancer people who reported regularly exercising at a high intensity compared to those who did not engage in physical exercise.
The mice exhibited a similar outcome, and the researchers were able to use the animal model to better understand what might be leading to the reduction in cancer. They found that aerobic activity significantly reduced the development of metastatic tumors in the lymph nodes, lungs, and liver of the mice.
"Examining the cells of these organs, we found a rise in the number of glucose receptors during high-intensity aerobic activity — increasing glucose intake and turning the organs into effective energy-consumption machines, very much like the muscles,” said Dr. Levy.
The authors presume this happens because the organs must compete for sugar resources with the muscles, which are known to burn large quantities of glucose during physical exercise. As a result, there is less glucose — therefore energy — available for the cancer to metastasize.
Furthermore, when a person exercises regularly, this condition becomes permanent: the tissues of internal organs change and become similar to muscle tissue, said Levy. “Our study, examining the internal organs, discovered that exercise changes the whole body, so that the cancer cannot spread, and the primary tumor also shrinks in size,” she said.
This is a good study, but we have to be careful in translating some of these observations in mice to human patients, says Roshani Patel, MD, medical director of breast surgery at the John Shore University Medical Center at Hackensack Meridian Health in New Jersey, who was not involved in the research.
That being said, the reduction in metastatic cancer found in this study does support findings from other research, says Dr. Patel. “There’s data that shows that exercise will reduce the risk of mortality from breast cancer by 46 to 50 percent and reduce the risk of recurrence by 31 to 50 percent, depending on which study we look at. By recurrence, we’re talking about both local but also metastatic recurrence of the cancer,” she says.
"Our results indicate that unlike fat-burning exercise, which is relatively moderate, it is a high-intensity aerobic activity that helps in cancer prevention," said Dr. Gepner. "If the optimal intensity range for burning fat is 65 to 70 percent of the maximum pulse rate, sugar burning requires 80 to 85 percent — even if only for brief intervals."
The authors believe that these findings suggest that people should include bursts of high intensity exercise into their exercise routines. “For example, a one-minute sprint followed by walking, then another sprint,” said Gepner.
“It must be emphasized that physical exercise, with its unique metabolic and physiological effects, exhibits a higher level of cancer prevention than any medication or medical intervention to date,” he said.
In general, these findings are a good reminder that we should all try to follow the guidelines on physical activity, says Patel. “Trying to be active and less sedentary is important for prevention of any cancer,” she says.
The recommendations are 150 minutes of moderate exercise (such as brisk walking) or 75 minutes of intense exercise (running or jogging) every week, along with two or more days of muscle-strengthening activities, according to the Centers for Disease Control and Prevention (CDC).