Physical Activity Linked With Reduced Risk of 13 Cancers

Partaking in leisure-time physical activity was associated with a reduction in risk for as many as 13 cancer types regardless of body size or smoking history, according to the results of a study published in JAMA Internal Medicine.

Among the risk reduction identified by Steven C. Moore, PhD, MPH, of the National Cancer Institute, and colleagues was a reduction of 20% or greater for 7 of 26 cancers explored by the study.

“Our results suggest that leisure-time physical activity may be associated with lower risk of a wider breadth of types of cancer than previously described, and they bolster the evidence for associations that were previously only weakly supported,” Moore and colleagues wrote.

In an editorial that accompanied the results, Lauren E. McCullough, PhD, of Emory University in Atlanta, and Kathleen M. McClain MS and Marilie D. Gammon, PhD, of the University of North Carolina, Chapel Hill, wrote: “These exciting findings by Moore et al underscore the importance of leisure-time physical activity as a potential risk reduction strategy to decrease the cancer burden in the United States and abroad.”

Moore and colleagues explored the association of leisure-time physical activity with cancer by pooling data from 12 prospective cohorts from the United States and Europe with self-reported physical activity between 1987–2004. The cohorts included 1.44 million participants and 186,932 cancers. They looked for associations related to 26 types of cancer. In the study, physical activity was defined as “activities done at an individual’s discretion that improve or maintain fitness or health.”

In all, an increase in leisure-time physical activity was associated with a reduction in risk for 13 of the 26 cancers examined by the study. More than a 20% reduction in risk for 7 cancers was identified among those patients with the highest level of physical activity compared with those with the lowest levels of activity: esophageal adenocarcinoma (hazard ratio [HR], 0.58), liver cancers (HR, 0.73), lung cancer (HR, 0.74), kidney cancer (HR, 0.77), gastric cardia (HR, 0.78), endometrium (HR, 0.79), and myeloid leukemia (HR, 0.80).

Risk reductions of between 10% and 20% were identified for myeloma, colon cancer, head and neck cancer, rectal cancer, bladder cancer, and breast cancer.

When the researchers adjusted the data for body mass index (BMI), the association for endometrial cancer was nullified and the HRs for esophageal, liver, kidney, and gastric cardia increased by between 5% and 11%, according to the study. Overall, 10 of the 13 cancers found to have associations with leisure-time physical activity remained statically significant after the BMI adjustment.

In addition to these reductions in risk, the pooled analysis also reveal an increased risk for malignant melanoma cancer (HR, 1.27) and prostate cancer (HR, 1.05) among those with higher rates of leisure-time physical activity.

Only the risk for lung cancer was modified by a patient’s smoking status.

“Moore and colleagues are among the first to provide evidence suggesting that, for some cancers, physical activity may act together with obesity to influence carcinogenesis,” wrote McCullough, McClain, and Gammon. “The precise mechanisms by which physical activity influences carcinogenesis are unknown. Resolving these underlying mechanisms should be a high research priority because this information would not only strengthen the biological plausibility of the physical activity–cancer association but could aid in identifying molecular targets for intervention.”