In recent years, one of the most provocative questions in cancer research has been whether a regular exercise habit can prevent certain cancers from taking hold.
The answer, as with any question related to cancer, is complicated. But a recent study published in The British Journal of Sports Medicine offered a glimpse of how regular physical activity affects the risk of prostate cancer, the most common male cancer in Ireland.
In one of the largest such efforts to date, researchers collected data between 1982 and 2019 from 57,652 Swedish men who had participated in at least two fitness tests to see if those who were more active were less likely to develop cancer. About 1 per cent were later diagnosed with prostate cancer. The team found that those who had improved in fitness over the years were 35 per cent less likely to have been diagnosed with the disease.
The finding is in line with much of the latest research on the relationship between fitness and cancer diagnosis. But while there has been extensive research on the relationship between exercise and conditions such as breast cancer, there has been less research specifically on prostate cancer. The chance of having prostate cancer rises for all men after 50; risk appears to run in families. One in eight men in Ireland will be affected by the disease and about 3,665 men are diagnosed with prostate cancer here every year.
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Some previous studies looking at the connection between physical activity and prostate cancer have been contradictory, according to Dr Kate Bolam, a co-author of the study. While some showed increased risk of prostate cancer for those who were physically active, others found a decreased risk. But many of those studies had small sample sizes or were biased toward healthier people, said Dr Bolam, a researcher at the Swedish School of Sport and Health Sciences. “Men who are generally more health-conscious,” she said, “are also good at going to the doctor when they are called for their prostate cancer screening tests”.
More testing means more diagnoses, including in men whose cancers will never progress. Sometimes cancer cells can exist in the prostate for one’s entire life and not be dangerous, so many men who are not tested and do not experience symptoms may never know they have prostate cancer.
The Swedish team was able to create a more nuanced picture by using a national database with hundreds of thousands of in-lab results, including fitness tests measuring how well the heart and the lungs supply oxygen to muscles. Unlike with studies that rely on patients to report their exercise habits, this gave experts objective measurements. The results clearly showed a link between physical activity and a reduced prostate cancer risk. It also showed that greater improvements in fitness were associated with a greater reduction in risk.
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This adds to a growing understanding of how important exercise is for prevention of cancer more generally. In 2019, a review by the American College of Sports Medicine found regular physical activity significantly reduced the risk of bladder, breast, colon, endometrial, esophageal adenocarcinoma, kidney and stomach cancers. The same analysis also found that having a regular exercise habit was tied to improved treatment outcomes and extended the life expectancies of those already living with cancer.
While it’s not clear exactly how this happens, experts said that one explanation may be that exercise helps fight cancer by enhancing how the immune system targets and eradicates cancer cells. “We know even a single bout of exercise helps our body release immune cells in our circulation,” said Neil Iyengar, a medical oncologist and physician scientist in New York city who was not involved in the study. “It also helps to improve the population of immune cells in our tissues that fight cancer cells.
“In somebody who exercises, you see more immune cells that are really able to kill cancer cells. Whereas for someone more sedentary, especially someone who is obese, you see the opposite.”
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Researchers do not yet know exactly the right dose and type of exercise that might be most effective, but the National Guidelines on Physical Activity for Ireland – produced by the Health Service Executive and Department of Health and Children – recommends children and young people should be active, at a moderate to vigorous level, for at least 60 minutes every day, while adults should aim for at least 30 minutes a day of moderate-intensity activity. Children and adults with a disability “should aim to be as active as the disability allows to meet the guideline for your age group”.
Both Dr Iyengar and Dr Bolam recommended starting simply. Find an activity that is enjoyable, and get moving. That could be playing with children or grandchildren, going for a walk or joining a recreational sports league. Consistency is key, they said, which is why it’s important to find activity that doesn’t feel like a chore.
“Everyone has a chance to do something that’s really cost-efficient here to decrease their risk of prostate cancer,” Dr Bolam said. “And that’s something that is wholly in our control.”
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