Exercise appears to protect against some cancers. Yes, something so simple as merely getting the recommended amount of 2 1/2 hours per week of exercise (e.g. brisk walks) really lowers the risk of 7 cancers: colon, breast, endometrial, kidney, myeloma, liver, and non-Hodgkin lymphoma.
The researchers analyzed 9 studies for a total of 755,459 individuals (median age 62 years, 53% females) who were followed for 10.1 years, and found that 50,620 cancers developed. They specifically looked at 15 cancers and found that exercise lowered the risk of 7 cancers. Some, but not all, were lowered in a dose response manner, that is, the more exercise, the bigger the protective effect (e.g. breast, colon, endometrial cancer). How much the cancer risk was lowered with exercise varied by types of cancer: colon (8%-14% lower risk in men), breast (6%-10% lower risk), endometrial (10%-18% lower risk), kidney (11%-17% lower risk), myeloma (14%-19% lower risk), liver (18%-27% lower risk), and non-Hodgkin lymphoma (11%-18% lower risk in women).
How much exercise was needed for a cancer protective effect? About 2 1/2 to 5 hours per week of moderate-intensity physical activity, such as brisk walking. The study looked at "leisure-time" exercise, which can include exercise, sports or any recreational activity which is typically "moderate to vigorous intensity".
The Physical Activity Guidelines from the US Department of Health and Human Services recommends that adults do at least 150 to 300 minutes of moderate-intensity physical activity a week, or 75 to 150 minutes of vigorous-intensity activity, or an equivalent combination of moderate- and vigorous-intensity activity. Brisk walking is moderate intensity physical activity. Bottom line: get out and move, move, move!
From Medical Xpress: Report links recommended physical activity levels to lower risk of seven cancers
A pooled analysis of nine prospective studies involving more than 750,000 adults finds that recommended amounts of leisure-time physical activity were linked to a lower risk for seven cancers, with several cancer types having a 'dose/response' relationship. The study was led by investigators at the National Cancer Institute, the American Cancer Society, and the Harvard T.H. Chan School of Public Health and appears in the Journal of Clinical Oncology.
While it's long been known that physical activity is associated with a lower risk of several cancers, less clear has been the shape of the relationship and whether recommended amounts of physical activity are associated with lower risk. Updated guidelines for activity now state that people should aim for 2.5 to 5 hours/week of moderate-intensity activity or 1.25 to 2.5 hours/week of vigorous activity. Moderate-intensity activities are those that get you moving fast enough or strenuously enough to burn off three to six times as much energy per minute as sitting quietly (3 to 6 METs). Vigorous-intensity activities burn more than 6 METs.
For the current analysis, investigators pooled data from nine prospective cohorts with self-reported leisure-time physical activity and follow-up for cancer incidence, looking at the relationship between physical activity with incidence of 15 types of cancer.
They found engaging in recommended amounts of activity (7.5 to 15 MET hours/week) was associated with a statistically significant lower risk of seven of the 15 cancer types studied, with the reduction increasing with more MET hours. Physical activity was associated with a lower risk of colon cancer in men (8% for 7.5 MET hours/week; 14% for 15 MET hours/week), female breast cancer (6%-10%), endometrial cancer (10%-18%), kidney cancer (11%-17%), myeloma (14%-19%), liver cancer (18%-27%), and non-Hodgkin lymphoma (11%-18% in women). The dose response was linear in shape for half of the associations and nonlinear for the others.
The analysis had some limitations: Even with 750,000 participants, patient numbers were limited for some cancers; participants were primarily white; there was a limited number of cohorts with detailed physical activity measures; and the authors relied on self-reported physical activity.
The authors conclude: "These findings provide direct quantitative support for the levels of activity recommended for cancer prevention and provide actionable evidence for ongoing and future cancer prevention efforts."