Numerous observational studies have shown an inverse relationship between self--reported exercise and risk of cancer, particularly breast, colorectal, and prostate cancers. However, investigators had not previously tested whether objective measures of cardiorespiratory fitness predict cancer incidence or cause-specific mortality.
Now, researchers find in a 17,000-man prospective study that more fit men, as measured by an exercise challenge test in middle age, are significantly less likely to develop lung or colorectal cancer and significantly less likely to die of lung, colorectal, or prostate cancer during the next 20 years.
“People think that it is known that physical activity is protective, but we are talking about a very specific measure of fitness, which is obtained on an exercise tolerance test,” said Susan Lakoski, MD, Assistant Professor of Medicine at the University of Vermont, who presented the data in a news conference before the American Society of Clinical Oncology Annual Meeting highlighting selected key research advances. “It is a formal measurement, like testing your LDL—you get a very specific number to target.
“It is known that [fitness] prevents cardiovascular disease and known that it helps in survival risk,” she continued. “But it hasn't been known if it prevents incident cancer and mortality after cancer diagnosis—and that is what is elucidated in the current study.”
To assess the potential effect of fitness on cancer risk and mortality, Lakoski and her team analyzed data from the prospective Cooper Center Longitudinal Study. Included were 17,049 men who had undergone a complete preventive health examination, including a cardiorespiratory fitness assessment, at a mean age of 50. The researchers used Medicare claims data to assess cancer diagnoses.
With a follow-up period of approximately 20 years, the researchers found a 68 percent reduction in the risk of being diagnosed with lung cancer in the men who were in the highest-fitness quintile compared with those in the lowest fitness quintile, after adjusting for other risk factors including age, body weight, smoking, cholesterol, blood pressure, and diabetes. Similarly, there was a 38 percent reduction in risk of colon cancer diagnosis for the most fit men compared with the least fit men. Prostate cancer incidence was not affected by fitness.
Among men who had a cancer diagnosis, the team found that all-cause and cancer-specific mortality were lower in those who were most fit in middle age compared with those who were least fit. Specifically, all-cause mortality was 58 percent lower in the most fit men compared with the least fit, after adjusting for other risk factors; cancer-specific mortality was reduced by 64 percent and cardiovascular disease mortality was reduced by 61 percent. All three differences were statistically significant.
“Even a small improvement in fitness, one MET [metabolic equivalent—a measure of the amount of oxygen used by the body during physical activity] made a significant difference in survival, reducing the risk of dying from cancer or cardiovascular disease by 14 and 23 percent, respectively,” Lakoski said. “This would equate to approximately a three-minute increase in a treadmill test, comparing a middle-aged man who achieved nine METs versus a middle-aged man who achieved 10 METs.”
Commenting on the study (Abstract 1520) during the news conference, ASCO President Sandra M. Swain, MD, said, “I think a really interesting finding is that even if men aren't obese they still have an increased risk of cancer if they are not fit—which suggests that everyone can benefit from improving their fitness.”
She noted that this is one of the first studies to explore fitness as a marker of future cancer risk and mortality. “That is what is really exciting about this. And it is a very large prospective study over a 20-year period of time.”