Although physical fitness is widely known to prevent cardiovascular disease, its impact on cancer is less clear. 

In an observational cohort study published in JAMA Oncology (2015; published online ahead of print) nearly 14,000 men underwent a treadmill-based fitness assessment and were then observed for an average 6.5 years. The men in the best shape had significantly lower rates of lung and colorectal cancer but, surprisingly, had higher rates of prostate cancer (PCa)—even after adjusting for several potentially confounding variables. 

The researchers hypothesized that physically fit men were more likely to undergo screening tests, presumably resulting in PCa over diagnosis. Fortunately, the fittest men also had the lowest overall cancer and cardiovascular mortality, so even if exercise did somehow contribute to PCa risk, its benefit still prevails.

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