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Cardio training protects smokers and ex-smokers against lung cancer

Unfit smokers can halve their risk of dying from lung cancer by improving their condition, write sports scientists from the University of South Carolina in Medicine & Science in Sports & Exercise. Ex-smokers can benefit from fitness too.

Cardio training protects smokers and ex-smokers against lung cancer
Smokers with an unhealthy lifestyle are 2500 percent more likely to develop lung cancer than non-smokers. For ex-smokers the outlook is less dramatic, but even for them the chance of developing fatal lung cancer remains high for many years after quitting. That's why scientists are searching for lifestyle factors that improve prospects for smokers and ex-smokers. One factor is physical exercise. But the jury's still out: some studies say that exercise protects against cancer – others say it does not.

These researchers tried to create more clarity by performing a big study on 38,000 men aged between 20 and 84. First the researchers measured the men's cardio-respiratory fitness [CRF] by getting them to run on a treadmill. The exertion level was gradually increased, and the researchers measured how long the men managed to keep on running. Technically speaking, the researchers subjected the men to a variation on the Balke maximal exercise test. The final scores in this test correlate with maximal oxygen uptake [VO2max].

Although cardio-respiratory fitness is 25-40 percent hereditary, researchers still regard it as a good indicator of physical exercise. The more often and the more intensively you exercise, the greater your cardio-respiratory fitness.

After the researchers had tested the men they tracked them for an average of 17 years, and recorded how many died from lung cancer. The data they collected is represented in the figure below.

Cardio training protects smokers and ex-smokers against lung cancer

If you set the likelihood of super-fit non-smoking men of developing lung cancer at 1, then the chance for unfit male smokers is 12 times as high. But if these men are just a bit fitter, the chance is reduced to factor 6. Smokers who manage to get themselves super-fit reduce their chances of developing fatal lung cancer to a factor 4.

The same is true for the ex-smokers: their chance of developing lung cancer is five times as high, if they're not fit. With just slightly better condition they halve the chance.

The figure below shows the same data, but in a simpler way. You can see that it's not necessary to get super-fit to reduce your chances of getting lung cancer by quite a lot. Just being a bit fit already has a good effect.

Cardio training protects smokers and ex-smokers against lung cancer

The researchers found no statistically significant reduction in the chance of developing lung cancer in fit non-smokers. That doesn’t mean that it isn't there, they think. The chance of non-smokers developing lung cancer is small. It's so small that you can't see well whether being fit protects non-smokers. If being fit does protect, then it would probably only show up in studies on larger numbers of people.

Med Sci Sports Exerc. 2010 May; 42(5): 872-8.

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