Measured levels of cardiorespiratory fitness appear to be as predictive of cancer risk and survival as they are of heart disease risk and survival, according to a 20-year, prospective study of more than 17,000 men.
The risks of lung and colorectal cancer were reduced 68% and 38%, respectively, in men with the highest level of cardiorespiratory fitness, compared with those who were the least fit.
Cardiorespiratory fitness did not significantly reduce prostate cancer risk, but the risk of dying was significantly lower among men with prostate, lung, or colorectal cancer if they were more fit in middle age (P less than .001).
Dr. Susan Lakosi
Prior studies have shown that being physically active is protective against cancer, but this study is unique because it looked at a very specific marker – cardiorespiratory fitness as measured by maximal exercise tolerance testing, Dr. Susan G. Lakoski said during a press briefing highlighting research to be presented at the upcoming American Society of Clinical Oncology (ASCO) meeting.
"Fitness as formal measurement is known to prevent cardiovascular disease and it’s also known that it helps in terms of survival risk, but what hasn’t been known is does it prevent incident cancer and mortality after cancer diagnosis and that’s what’s elucidated in the current study," said Dr. Lakoski, director of the cardiovascular prevention program for cancer patients at the University of Vermont, Burlington.
She noted that several organizations, including the President’s Council on Fitness, Sports & Nutrition, are trying to measure fitness formally and that the American Heart Association has issued policy statements that fitness should be measured and normative values developed to determine cardiovascular risk.
"Fitness is a formal measurement; it’s sort of like measuring your LDL cholesterol, you get a very specific number to target," Dr. Lakoski said. "When you ask someone about their physical activity, you don’t get that information."
The 17,049 men in the study underwent exercise tolerance testing with a treadmill or bicycle and risk factor assessment at an average age of 50 years as part of the Cooper Center Longitudinal Study in Dallas. Metabolic equivalents (METs) were used to record the men’s cardiorespiratory fitness (CRF) and to place them into five CRF quintiles. Lung, colorectal and prostate cancers were assessed using Medicare claims data at Medicare age, and cause-specific mortality was determined after cancer diagnosis.
Over the 20 years of follow-up, 2,885 men were diagnosed with prostate, lung, or colorectal cancer and 769 died.
Compared with men in the lowest CRF quintile, hazard ratios (HR) for incident lung, colorectal and prostate cancer among men in the highest quintile were 0.32 (P less than .001), 0.62 (P = .05) and 1.13 (P = .14), after researchers adjusted for such risk factors as smoking, body mass index, and age, Dr. Lakoski reported.
In men who developed cancer, both cancer-specific mortality and cardiovascular-specific mortality declined across increasing CRF quintiles (P values less than .0001).
Even a single MET increase reduced the risk of dying from cancer and cardiovascular disease by 14% and 23%, respectively (HR, 0.86; HR, 0.77; P less than .001 for both measures), Dr. Lakoski said.
Another striking finding is that even if men aren’t obese, they still have an increased risk of cancer if they aren’t fit, "which suggests that everyone can benefit from improving their fitness," Dr. Sandra Swain, ASCO president and medical director of the Washington (D.C.) Cancer Institute told reporters.
"The findings make clear that patients should be advised that they need to achieve a certain fitness level, and not just be told that they need to exercise," Dr. Swain noted in a statement.
"A primary care physician should start to think about fitness in the same light as body weight or high cholesterol," Dr. Lakoski said in an interview. "Fitness is a key risk factor for survival, and based on this study, an important factor to measure to assess future cancer risk and prognosis in men."
The study did not evaluate whether a particular type of exercise contributed more consistently to cardiovascular fitness, but in general, activities performed at high intensity, regardless of type, are the best way to improve fitness, she said.
Additional research is needed to determine fitness and cancer risk in women, fitness and risk of all major site-specific cancers and the necessary change in fitness to prevent cancer, Dr. Lakoski observed.
Assessment protocols and norms are available for CRF testing from the Cooper Institute.
Dr. Lakoski reported no relevant disclosures.