"Very fit men in their late 40s are less likely to get lung cancer and colorectal cancer than unfit men," says BBC News as it reports on a new US study.
The study involved a comprehensive fitness test of 13,949 US men. They were split into three fitness groups: lowest 20%, middle 40% and top 40%, and followed for an average of 6.5 years to see if fitness affected their chance of developing certain cancers.
Perhaps surprisingly, men in the top group actually had a 22% higher risk of prostate cancer.
One obvious point is that men who exercise to stay fit are usually healthy in other ways too, such as eating a healthy diet and abstaining from alcohol. This could have influenced the results.
Still, there is evidence that exercise alone can reduce your cancer risk. Information provided by Cancer Research UK explains how exercise can reduce inflammation and prevent bowel damage, which may reduce cancer risk.
With its proven effect of preventing heart disease, regular exercise is always a good idea, whatever your age or sex. Read more about the benefits of exercise.
Where did the story come from?
The study was carried out by researchers from the University of Vermont, the University of Texas Southwestern Medical Center, Duke University Medical Center in Dallas, and the Memorial Sloan Kettering Cancer Center in New York.
It was funded by the US National Institute of General Medical Sciences, the National Institutes of Health, and the National Cancer Institute.
Generally, the UK media reported the story accurately, but none mentioned the possibility that diet could be accounting for some of the improvements seen, not just fitness.
What kind of research was this?
This was a longitudinal study looking at whether cardiorespiratory fitness (having both a healthy heart and lungs) prevents or improves outcomes in cancer.
It used data already collected as part of the long-running Cooper Center Longitudinal study.
There are many risk factors for cancer, including age, diet and physical activity. This study focused on fitness and whether this helped men develop fewer cancers, and survive better if they did develop cancer.
What did the research involve?
The research analysed fitness data on 13,949 US men collected as part of the Cooper Center Longitudinal study between 1971 and 2009.
The men were split into three fitness groups: lowest 20%, middle 40% and top 40%, and followed for an average of 6.5 years to see if fitness levels affected their chance of developing lung, colorectal or prostate cancer.
Fitness was assessed using an incremental treadmill test, which tests a person's ability to run to exhaustion.
The outcomes researchers were most interested in studying were:
- new cases of prostate, lung and colorectal cancer
- death from any cause for men developing cancer over the age of 65
- cause-specific death, such as cardiovascular disease, for men developing cancer over the age of 65
Cancer diagnosis and notification of death came from Medicare claims data, which is the US government health insurance system covering people over 65.
The statistical analysis took account of many common cancer risk factors, but not diet or the stage of cancer at diagnosis.
The confounding factors adjusted for included:
- examination year
- body mass index (BMI)
- total cholesterol level
- systolic blood pressure
- diabetes mellitus
- fasting glucose level
What were the basic results?
Over the study period, 181 men were diagnosed with colon cancers, 200 with lung cancers, and 1,310 with prostate cancers.
The main message from the results is that exercise is very good at reducing the risk of developing lung and colorectal cancer, as well as helping reduce the risk of dying from cancer or cardiovascular disease. The pattern of risk for prostate cancer was less clear.
Men in the fittest group were 55% less likely to develop lung cancer (hazard ratio [HR] 0.45; 95% confidence interval [CI], 0.29 to 0.68), and 46% less likely to develop colorectal cancer (HR, 0.56; 95%; CI, 0.36 to 0.87), compared with men in the lowest fitness group. The risk of prostate cancer was actually 22% higher (HR 1.22; 95%; CI, 1.02 to 1.46).
Similar benefits were seen comparing the middle exercise group with the lowest exercise group, but the risk differences were slightly smaller.
For example, risks were 43% lower for lung cancer and 33% lower for colon cancer compared with the lowest fitness group. This time there was no difference for prostate cancer. This analysis covered cancers diagnosed at any age.
Looking only at cancers diagnosed after the age of 65, the fittest group were 32% less likely to die from cancer compared with men in the lowest fitness group (HR, 0.68; 95%; CI, 0.47 to 0.98) – this included prostate cancer.
They were also 68% less likely to die from cardiovascular disease after a cancer diagnosis (HR, 0.32; 95%; CI, 0.16 to 0.64) compared with the least fit men.
How did the researchers interpret the results?
The authors concluded that, "There is an inverse association between midlife CRF [cardiorespiratory fitness] and incident lung and colorectal cancer, but not prostate cancer. High midlife CRF is associated with lower risk of cause-specific mortality in those diagnosed as having cancer at Medicare age [over 65]."
This study shows that cardiovascular fitness is likely to reduce men's chances of developing lung and colorectal cancer, and appears to boost survival from cancer or cardiovascular disease in those diagnosed after the age of 65. This was based on comparing the top 40% of fittest men with the 20% least fit.
The study focused on fitness and took account of major risk factors for cancer, such as smoking and blood pressure. However, it left out one important risk factor: diet. What people eat and drink is known to affect cancer risk.
The fittest group may also have been the healthiest in terms of eating well and drinking alcohol within safe limits. This probably accounted for some of the risk reductions seen in this study. What proportion? We don't know.
This, in effect, makes this a study of healthiness incorporating fitness and diet. The evidence that eating well and being active reduces the risk of cancer, heart disease, stroke and diabetes is already well established. Studies have also shown regular physical activity also benefits our mental health.
Read more about reducing your cancer risk.
Although fitter men over the age of 65 diagnosed with cancer had better survival rates, there are other unmeasured factors that could have contributed. It is not known whether the fitter people were diagnosed with cancer at an earlier stage, which would have increased their chance of survival.
There was also a counterintuitive finding worth noting. The fittest group were more likely to be diagnosed with prostate cancer than the least fit. This is important, as prostate cancer risk was much higher than lung or colon cancer in the sample.
The study authors thought this might be because fitter men go for more cancer tests in the US than unfit men, so therefore the cancer is discovered and diagnosed more often in that group.
It could also be the case that men in the fittest group would probably live longer, and prostate cancer is an age-related disease.
But we don't know this for sure, and there could be other explanations worth investigating.
Would you know if you had prostate cancer? Read more about prostate cancer symptoms.