We have long known that regular exercise can prevent cardiovascular disease. For the past 20 years, however, evidence has been accumulating that such exercise can prevent some cancers, especially those involving the colon and breast. The list of potentially preventable cancer types has been growing, with evidence now suggesting that the prevention may also include cancers of the lung, uterus, and prostate gland.
Regarding cancer in men, prostate cancer is the most prevalent form, being diagnosed in approximately 223,000 men yearly, but fatalities are relatively low, at 29,000.
Lung cancer is found in about 110,000 yearly, and causes death in 88,000
Colorectal cancers are diagnosed in 72,700 men, and fatal in 27,000.
In women, a whopping 230,480 new cases of invasive breast cancer are being diagnosed yearly in the U.S. A total of 39,500 are expected to die from this disorder.
THE ROLE OF EXERCISE
In 2003, a paper in the journal Medicine & Science in Sports & Exercise reported that more than a hundred population (epidemiologic) studies on the role of physical activity and cancer prevention have been published. The authors noted that:
“The data are clear in showing that physically active men and women have about a 30-40 percent reduction in the risk of developing colon cancer, compared with inactive persons … With regard to breast cancer, there is reasonably clear evidence that physically active women have about a 20-30 percent reduction in risk, compared with inactive women. It also appears that 30-60 min/day of moderate- to vigorous-intensity physical activity is needed to decrease the risk of breast cancer, and that there is likely a dose-response relation.”
These studies were collected mainly by questionnaires about exercise regularity and subsequent development of cancers. Although this type of information is convincing, we now have even more conclusive results derived from careful assessment of physical fitness and development of cancer, at least in men.
According to a 20-year, prospective study of more than 17,000 men at the Cooper Institute in Dallas, Texas, measured levels of cardiorespiratory fitness appear to be as predictive of cancer risk and survival as they are of heart disease risk and survival.
Their data showed that 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.
Although cardiorespiratory fitness did not significantly reduce prostate cancer incidence, the risk of dying was significantly lower among men with prostate, lung, or colorectal cancer if they were more fit in middle age.
Although prior studies have shown that being physically active is protective against cancer, this study is unique because it looked at a very specific marker – cardiorespiratory fitness as measured by maximal exercise tolerance testing.
What was unexpected was that evidence of fitness not only predicts prevention of cancer but also even mortality after cancer has already been diagnosed.
Thus quantitative measurements of fitness might be compared with measuring your cholesterol, providing us with a very specific number to target. Merely asking someone about his/her physical activity doesn’t provide 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 a long term study. 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 had been diagnosed with prostate, lung, or colorectal cancer, and of these, 769 died. .
Compared with men in the lowest CRF fitness quintile, hazard ratios for developing lung and colorectal cancer men in the highest fitness group were 68% lower for lung cancer and 32% lower for colorectal cancer, after researchers adjusted for such risk factors as smoking, body mass index, and age.
In men who had already developed all these cancers, mortality also declined across the higher the fitness groups.
Even a single MET increase in fitness reduced the risk of dying from cancer and cardiovascular disease by 14% and 23%, respectively.
Another striking finding is that even if men aren’t obese, they still have an increased risk of cancer if they aren’t fit, suggesting that everyone can benefit from improving their fitness. The findings also suggest that, ideally, individuals should be advised that they need to achieve a certain fitness level, and not just be told that they need to exercise
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.
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.
In the meantime, plenty of exercise is fit for all!