Regular Exercise Linked to Reduced Risk of Several Cancers

Roxanne Nelson, RN, BSN

December 31, 2019

Just in time for New Year's resolutions comes a finding that may help with motivation: regular exercise appears to reduce the risk of developing several types of cancer, and there is a hint that there may a dose-response relationship.

"Physical activity guidelines have largely been based on their impact on chronic diseases like cardiovascular disease and diabetes," said study coauthor Alpa Patel, PhD, senior scientific director of epidemiology research at the American Cancer Society in Atlanta, Georgia.

"These data provide strong support that these recommended levels are important to cancer prevention, as well," she said in a statement.

The findings come from a large meta-analysis of nine prospective cohorts with a total of 755,459 individuals.

Individuals who engaged in moderate-intensity activity for 2.5 to 5 hours per week had a significantly lower risk of several cancers, including breast, colon (men only), endometrial, kidney, myeloma, and liver cancer and non-Hodgkin lymphoma (women only).

The strength of associations between the recommended amounts of physical activity as compared with no activity varied from a 6%-10% lower risk for breast cancer to an 18%-27% lower risk of developing liver cancer.

"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," write the authors, led by Charles E. Matthews, PhD, from the Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland.

The study was published online December 26 in the Journal of Clinical Oncology.

Matthews and colleagues emphasize that this is an observational study and therefore cannot demonstrate causality, nor can effects of unmeasured or residual confounding be completely ruled out. But that said, they also note that these results "provide the best available description of the dose response for leisure-time physical activity and cancer risks of which we are aware."

Details of the Findings

It is already well established that physical activity is associated with a lower risk of colon and breast cancer, the authors note. In addition, the 2018 US Physical Activity Guidelines Advisory Committee noted that there is strong evidence that physical activity is associated with a lower risk of several different cancers, including endometrial, bladder, esophageal adenocarcinoma, kidney, and gastric.

However, it remains unclear whether the recommended amounts of physical activity (2.5-5 hours/week of moderate-intensity activity or 7.5-15 metabolic equivalent task [MET] hours/week) are associated with a lower risk of cancer, the authors note.

So they set out to answer that question.

The team obtained data from 9 prospective cohorts that had self-reported leisure-time physical activity and follow-up for cancer incidence, and then assessed the relationship of physical activity to 15 cancers. There were a total of 755,459 individuals included in the analysis, none of whom had cancer at the beginning of follow-up. The cohorts were generally consistent in reported amounts of leisure-time physical activity, with 7 reporting a median of between 7.6 and 8 MET hours/week.

At 10.1 years of follow-up, there were 50,620 incident cancers.

Overall, there was a statistically significant association between higher levels of physical activity with a lower risk for breast, colon, endometrial, and kidney cancer, as well as esophageal adenocarcinoma and head/neck and liver cancer (P overall <.05). Associations for both gastric cardia and myeloma reached borderline significance (P = .05).

When evaluated by sex, an association was seen with colon cancer in men (HR, 0.81; 15 vs 0 MET hours/week) but was more attenuated in women (HR, 0.94). The opposite was true for non-Hodgkin lymphoma, where an association was observed in women (HR, 0.82) but not in men (HR, 1.00).

The authors also looked at what effect doing the recommended amount/intensity of exercise had on cancer risk. They found that individuals who achieved the recommended amounts of activity (7.5-15 MET hours/week) had a statistically significant lower risk of 7 of the 15 cancer types that were included in the study: 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).

Subset Associations

In a subset of the cohort (n = 309,881), the authors evaluated adjusted associations separately for moderate- and vigorous-intensity physical activity in the nine cancer types that appeared to be significantly associated with exercise.

Overall, breast and kidney cancer were significantly associated with moderate-intensity activity, whereas endometrial cancer risk showed significant associations with vigorous intensity activity. Colon cancer showed borderline significance for both moderate-intensity (P = .06) and vigorous-intensity (P = .10) activity.

The study was supported in part by the National Institutes of Health (NIH) Intramural Research Programs of the National Cancer Institute and the National Institute on Aging. Coauthor Brigid M. Lynch reports travel, accommodations, and expenses with Merck Sharp & Dohme. Coauthor Sven Sandin reports stock and other ownership interests with AstraZeneca.

J Clin Oncol. Published online December 26, 2019. Full text

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