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Improving cardiorespiratory fitness may lower men's prostate cancer risk, results from a Swedish study suggested.

The retrospective study showed that an overall increase in absolute cardiorespiratory fitness (as measured by changes in VO_2max) was associated with a 2% reduced risk of prostate cancer incidence (HR 0.98, 95% CI 0.96-0.99), when adjusted for baseline fitness, age, education, year of last test, BMI, and smoking.

However, the study also showed that a change in cardiorespiratory fitness had no association with prostate cancer mortality.

When researchers looked at differences between groups, they found that men who had an annual increase in cardiorespiratory fitness of at least 3% had a 35% reduced risk of developing prostate cancer compared to men whose fitness decreased by 3% (HR 0.65, 95% CI 0.49-0.86), reported Kate A. Bolam, PhD, of the Swedish School of Sport and Health Sciences in Stockholm, and colleagues.

"Although highly complex in nature, these investigations that aim to understand potential mechanisms behind the beneficial role of physical activity for preventing cancer will lead to more targeted prevention recommendations," wrote Bolam and colleagues in the . "The results of this study highlight the important role of supporting the general public to increase their CRF [cardiorespiratory fitness] or aim to reach moderate fitness levels."

When the participants were stratified according to their cardiorespiratory fitness at baseline, a significantly reduced risk of developing prostate cancer (15% lower) was only seen in men with a moderate level of fitness to begin with.

"It may be that improving one's CRF from an already high baseline does not confer any discernible additional benefits," the authors speculated.

In this prospective cohort study, the authors used the workplace health profile assessment database of the Health Profile Institute in Stockholm, which included data on more than 180,000 men assessed between 1982 and 2019.

Of these men, 58,971 met the study criteria of having undergone at least two cardiorespiratory fitness tests on a cycle ergometer spaced at least 11 months apart. After excluding as outliers those men who experienced a fitness decrease or increase of over 20% per year, the study cohort included 57,652 men. Their mean age was 41.4 years, and average BMI 26 at baseline.

At a mean follow-up of 6.7 years, 592 of these men (1%) had been diagnosed with prostate cancer, while 46 (0.08%) died with prostate cancer as the primary cause of death.

The authors noted that while an association between physical activity levels and incidence and mortality has been seen in a number of cancer types, the evidence for prostate cancer has been inconclusive.

In fact, contrary to other cancer types, several studies that examined the relationship between cardiorespiratory fitness at one time point compared to prostate cancer incidence showed an increase in cardiorespiratory fitness actually magnified the risk of prostate cancer.

For example, in a in the British Journal of Sports Medicine, researchers found that having good fitness was associated with reduced risk of developing nine different types of cancer, with risk reductions ranging from 5% to 42%. However, higher cardiorespiratory fitness was associated with a 7% heightened risk of prostate cancer.

"[T]he reason for these positive associations may not be due to a 'true' increased risk for those with higher CRF, but in part due to the influence of higher prostate cancer screening rates in men with higher CRF," Bolam and colleagues wrote, adding that the findings from the present study "contribute significantly to our knowledge of the relationship between CRF and prostate cancer as it is the first study to investigate change in CRF rather than CRF at a single time point, and to focus on prostate cancer specifically."

As for the lack of association between cardiorespiratory fitness and prostate cancer mortality, the authors suggested that the few prostate cancer-related deaths reported in the study might not have sufficiently powered detection of any associations.

They also pointed out that there is a competing mortality risk with chronic diseases such as cardiovascular and metabolic disease that are associated with prostate cancer treatment side effects.

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