Greater levels of leisure-time physical activity (defined as exercise done at one's own discretion to improve or maintain fitness or health, including walking, running, swimming, and other moderate to vigorous intensity activities) were associated with a lower risk of developing 13 types of cancer, according to a study by National Cancer Institute (NCI) investigators published in JAMA Internal Medicine.
In an analysis of data from 1.44 million people (age range = 19-98 years) in the United States and Europe, Steven C. Moore, PhD, and colleagues confirmed a benefit of physical activity on cancer risk – supporting its role as a key component of population-wide cancer prevention and control efforts.
"Health-care professionals counseling inactive adults should promote physical activity as a component of a healthy lifestyle and cancer prevention," Dr. Moore said in a press release from the NCI.
Dr. Moore and colleagues measured levels of leisure-time physical activity and cancer diagnoses over a period of 11 years to determine the relationship between activity level and cancer risk.
During follow-up, 187,000 new cancer diagnoses occurred. The median level of activity in the study population was approximately 150 minutes of moderate-intensity activity on a weekly basis, which is comparable to minimum U.S. recommended level of physical activity, the authors noted.
Physical activity has been previously linked to colon, breast, and endometrial cancers and, according to the study by Dr. Moore and colleagues, it is now also linked to a number of additional cancers, including myeloma and myeloid leukemia. Comparing the cancer risk between people who had high levels of leisure-time physical activity with those who had low activity levels, the hazard ratios (HRs) were:
- esophageal adenocarcinoma: 0.58 (95% CI 0.37-0.89)
- liver: 0.73 (95% CI 0.55-0.98)
- lung: 0.74 (95% CI 0.71-0.77)
- kidney: 0.77 (95% CI 0.70-0.85)
- gastric cardia: 0.78 (95% CI 0.64-0.95)
- endometrial: 0.79 (95% CI 0.68-0.92)
- myeloid leukemia: 0.80 (95% CI 0.70-0.92)
- myeloma: 0.83 (95% CI 0.72-0.95)
- colon: 0.84 (95% CI 0.77-0.91)
- head and neck: 0.85 (95% CI 0.78-0.93)
- rectal: 0.87 (95% CI 0.80-0.95)
- bladder: 0.87 (95% CI 0.82-0.92)
- breast: 0.90, 95% CI 0.87-0.93)
The association between physical activity and cancer were similar even in subgroup analyses comparing people who were of normal weight and those who were overweight, as well as smokers and never-smokers.
There are a number of mechanisms through which physical activity could affect cancer risk, the authors noted. "It has been hypothesized that cancer growth could be initiated or abetted by three metabolic pathways that are also affected by exercise: sex steroids (estrogens and androgens); insulin and insulin-like growth factors; and proteins involved with both insulin metabolism and inflammation," Dr. Moore and colleagues wrote.
Source: Moore SC, Lee I, Welderpass E, et al. Leisure-time physical activity and risk of 26 types of cancer in 1.44 million adults. JAMA Intern Med. 2016 May 16. [Epub ahead of print]; National Cancer Institute news release, May 16, 2016.