A prospective analysis of physical activity and cancer.

Previous studies have suggested that increased physical activity may be protective against colon cancer. Most of these studies measured activity indirectly. The present study evaluated several direct measurements of physical activity and also resting heart rate as determined from an electrocardiogram. Increased activity was consistently associated with a decreased relative risk of colon cancer for each measure of activity. The colon cancer relative risk estimates for the middle and upper tertiles of a physical activity index (compared with the lower tertile) were 0.56 (95% confidence interval (CI) 0.39-0.80) and 0.71 (95% CI 0.51-0.99), respectively. Relative risk of colon cancer associated with moderate or heavy activity at home/recreation (compared with mostly sitting) was 0.66 (95% CI 0.49-0.88). A similar comparison of activity at work resulted in a relative risk estimate of 0.72 (95% CI 0.52-1.00). Relative risk of colon cancer increased significantly (p = 0.027) with increasing resting heart rate. Relative risks associated with physical activity were also evaluated for cancers of the stomach, rectum, lung, prostate, and urinary bladder. An increased relative risk of stomach cancer was associated with several measures of increased activity, but these results are preliminary and additional research is necessary to further evaluate this finding.