JAMA Oncology: 17 hours of light physical activity per week reduces risk of colorectal cancer

Maintaining moderate physical activity—about 17 hours per week—can significantly reduce the risk of developing cancers of the digestive system. This conclusion was reached by researchers from the Harvard T.H. Chan School of Public Health in Boston. The study findings were published in the journal JAMA Oncology.

The researchers analyzed data from three large cohort studies involving about 231,000 US residents with an average age of 32. At the start of the studies, participants had no history of cancer or cardiovascular disease. Every two to four years, they completed questionnaires about their health, level of physical activity, and diet.

Over several decades of observation, a total of 6,358 cases of digestive system cancer and 3,791 deaths were recorded. Researchers found that the risk of developing and dying from these types of cancer was significantly lower among people who regularly engaged in leisure-time physical activity.

The strongest effect was observed when maintaining about 17 metabolic equivalent task (MET)-hours per week. This corresponds to five hours of brisk walking or two hours of running. Such a level of activity reduced the risk of developing cancers of the digestive system by about 17%. Moreover, increasing the intensity beyond this level did not bring additional benefit.

According to study author Dr. Yiwen Zhang, the protective effect is not solely due to body weight reduction.

Physical activity likely has a systemic anti-cancer effect; it improves insulin sensitivity, reduces inflammation levels, and strengthens the immune system. In addition, exercise may promote better digestion by shortening the contact time of potential carcinogens with the intestinal walls, the researcher noted.

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