Being fit earlier in life is associated with a reduced risk, in some cases of up to 42%, of developing nine different types of cancer in later life, according to a large long-term study.
While exercise has been previously linked with a lower risk of certain cancers, long-term and large cohort studies on multiple cancer sites are sparse.
The new study, published in the British Journal of Sports Medicine, drew from data from more than 1 million male Swedish conscripts between 16 and 25, who were followed for an average of 33 years from 1968 to 2005. The results suggested that good cardiorespiratory fitness – an individual’s ability to engage in sustained aerobic exercises such as running, cycling, and swimming – was associated with a 42% reduced risk of lung cancer, a 40% reduced risk of liver cancer and a 39% reduced risk of oesophageal cancer.
It was also associated with a lower risk of head and neck, stomach, pancreatic bowel and kidney cancer.
Higher cardiorespiratory fitness appeared to be associated with a 7% heightened risk of prostate cancer and a 31% heightened risk of skin cancer – although it is possible that more frequent prostate cancer screening and sunlight exposure might account for these findings.
The lead researcher, Dr Aron Onerup – at the University of Gothenburg in Sweden, said he was surprised by some of these broad associations across several organ systems and “by the consistent associations between cardiorespiratory fitness and cancers in the gastrointestinal tract”.
Addressing the unexpected rise in risk for prostate and skin cancers, Onerup said subsequent studies had indicated men with higher fitness levels were more likely to be diagnosed with non-fatal prostate cancers.
However, this study “doesn’t fully take into account the effect of diet, alcohol and smoking, which are more likely to affect your risk of developing cancer”, said Dr Claire Knight, senior health information manager at Cancer Research UK.
Overall, the results are compelling and strengthen the incentive for promoting interventions aimed at increasing cardiorespiratory fitness in youth throughout school and university years, said Dr Mark Hamer, professor of sport and exercise medicine at University College London.
While other researchers warned about drawing cause and effect conclusions from this kind of observational study, Hamer added: “This long follow-up period pretty much rules out issues of reverse causation (existing disease driving poor fitness and early death) that many previous studies struggle to deal with.”
“While cardiorespiratory fitness was associated with half of the cancer sites included, this was less true for muscle strength. So, while we did not look at activities in our study, this might indicate that aerobic activities such as running, biking, sports, swimming are more likely to be associated with cancer risk than resistance training is,” said Onerup.
Reducing cancer risk is not the only reason to exercise. There are compound benefits across emotional health and preventing cardiovascular disease. Onerup said “some physical activity is better than none, that more physical activity is better for optimal health outcomes”, and emphasised thatit is never too late to get fit to reap health protective benefits.
As for how much exercise, Knight recommended 150 minutes of exercise a week, but said: “It’s fine to build up activity over time and there are lots of ways to be more active. You don’t need to run a marathon or join a gym – anything that gets you warmer, slightly out of breath, and your heart beating faster counts.
“It doesn’t matter if you go for a brisk walk, a cycle with a friend, or even get the housework done, these could all count as ways to be active.”