Physical activity is associated with reduced breast and colon cancer mortality, but there is insufficient evidence on the association for other cancer types, according to a study published in the Journal of the National Cancer Institute.

Improvements in cancer treatment and screening have allowed cancer survivors to live longer and as a result, cancer survivors frequently look at information about how lifestyle factors like exercise can affect their prognosis.

Multiple observational studies and randomised control trials (RCTs) have looked at the effects that physical activity can have on cancer survivors.

To examine the association between physical activity and cancer survival, Rachel Ballard-Barbash, M.D., of the Applied Research Program in the Division of Cancer Control and Population Sciences at the National Cancer Institute and colleagues reviewed 45 articles reporting both observational studies and randomised controlled trials (RCTs) that looked at the relationship between physical activity and mortality and/or cancer biomarkers among cancer survivors.

The studies were published between January 1950 and August 2011.

The researchers found that the RCTs with biomarker endpoints suggest that exercise may provide benefits to survivors' insulin levels, reduce inflammation, and, possibly, improve immunity.

The strongest evidence is for breast cancer survivors: most studies showed a statistically significant reduced risk of breast cancer and all-cause mortality associated with exercise.

The next strongest evidence was for colorectal cancer survivors.

The authors point out that because of the diversity of the studies, it would be impossible to extrapolate specific recommendations on type and timing of physical activity. However, they can attest to the overall safety, physical and mental benefits of exercise for cancer survivors. They add that future RCTs should look at different types of exercise, as well as how obesity, weight loss, and cancer treatments may influence the effects of exercise on biomarkers. Also, how exercise may influence comorbidities in cancer survivors should be studied, they write.

In an accompanying editorial, Edward L. Giovannucci, M.D., ScD, of the Department of Nutrition at the Harvard School of Public Health, writes that physical activity may extend the life-span of the cancer survivor, as well as their quality of life. "Even though direct effects of physical activity on cancer are not definitely proven, given that physical activity is generally safe, improves quality of life for cancer patients, and has numerous other health benefits, adequate physical activity should be a standard part of cancer care," he writes.

Source: Journal of the National Cancer Institute