Physical activity linked to lower breast, colon cancer death rates
A meta-analysis has demonstrated an association between physical activity and reduced all-cause, breast cancer-specific, and colon cancer-specific mortality.
A team led by Rachel Ballard-Barbash, MD, of the Applied Research Program in the Division of Cancer Control and Population Sciences at the National Cancer Institute, Bethesda, Maryland, systematically reviewed studies that examined relationships between physical activity and mortality (all-cause and cancer-specific). The investigators identified 45 articles on observational studies and randomized controlled trials, published between January 1950 and August 2011, in which the relationship between physical activity and mortality and/or cancer biomarkers among cancer survivors was examined.
Ballard-Barbash and colleagues found consistent evidence from 27 observational studies supporting a link between physical activity and reduced all-cause mortality and reduced mortality from breast or colon cancer. The strongest evidence was for survivors of breast cancer, with most studies showing a statistically significant reduction in risk of breast cancer mortality and all-cause mortality associated with exercise. The next strongest evidence was for survivors of colon cancer, but insufficient evidence was found to suggest an association between physical activity and mortality for survivors of other cancers.
The randomized controlled trials that included biomarker endpoints indicated that exercise may result in beneficial changes in the circulating levels of insulin, insulin-related pathways, inflammation, and, possibly, immunity. However, evidence is still preliminary.
As the researchers noted in Journal of the National Cancer Institute, the diversity of the studies reviewed make it impossible to shape specific recommendations on type and timing of physical activity, but Ballard-Barbash's group could attest to the overall safety and physical and mental benefits of exercise for cancer survivors. The authors added that future randomized controlled trials of exercise with biomarker and cancer-specific disease endpoints, such as recurrence, new primary cancers, and cancer-specific mortality in cancer survivors are warranted.
In an accompanying editorial, Edward L. Giovannucci, MD, ScD, of the Department of Nutrition at the Harvard School of Public Health, Boston, Massachusetts, expressed his belief that adequate physical activity should be a standard part of cancer care because it is generally safe, improves quality of life for cancer patients, and has numerous other health benefits.