Boosting fitness levels linked to lower prostate cancer risk

In a recent study published in the British Journal of Sports Medicine, researchers investigate the relationship between changes in adult cardiorespiratory fitness (CRF) and the incidence and mortality of prostate cancer.

Study: Association between change in cardiorespiratory fitness and prostate cancer incidence and mortality in 57,652 Swedish men. Image Credit: Peakstock / Shutterstock.com

Background 

In contrast to other cancers, such as those affecting the breast, colon, and lungs, wherein preventable risk factors are well-established, it remains unclear which factors increase an individual’s risk of prostate cancer. The primary known risks include developmental factors and being overweight or obese, particularly for advanced prostate cancer; however, evidence is limited for non-advanced cases.

While physical activity influences various cancer types, its impact on prostate cancer remains unclear, with studies showing mixed results. CRF, which is associated with lower systemic inflammation and improved health markers, has been less explored in prostate cancer research. The conflicting findings in CRF and physical activity studies, which are potentially influenced by higher screening rates among fitter individuals, emphasize the need for additional studies. 

About the study 

Researchers analyzed data from the Health Profile Assessment (HPA) database managed by the Health Profile Institute in Stockholm, Sweden. The HPA offered to employees of associated companies at no cost, included lifestyle questionnaires and a submaximal ergometer CRF test.

CRF was measured using the validated Åstrand test, and participants were categorized into groups based on more than 3% changes in absolute CRF. Prostate cancer incidence and mortality data were obtained from Swedish national health registries linked to the HPA database.

Statistical analysis involved Cox proportional hazard regression models to examine the relationship between CRF changes and prostate cancer. The researchers adjusted for factors like age, body mass index (BMI), and smoking. Sensitivity analysis was conducted to mitigate reverse causality concerns.

All analyses adhered to established statistical assessment guidelines and were performed using R Studio and associated packages.

Study findings 

Between 1982 and 2019, data were acquired from 181,673 men, 58,971 of whom met the criteria of having two or more CRF tests with a minimum gap of 11 months between the tests.

After excluding 1,319 individuals for extreme CRF changes, the sample consisted of 57,652 men with a mean age of 41.4 years and an average BMI of 26.0 kg/m². Among these individuals, 592, or 1% of the study cohort, were diagnosed with prostate cancer, 46 of whom died from the disease.

At baseline, the absolute and average relative CRF values were 3.12 L/min and 37.4 mL/kg/min, respectively. There was a slight decline in both relative and absolute CRF over an average of 4.9 years between tests. The follow-up period for incidence analysis averaged 6.7 years from the last CRF test.

No association between baseline or last-test CRF and prostate cancer risk was observed after adjusting for factors like age, BMI, and smoking status. However, in unadjusted analyses, higher CRF at both time points was inversely associated with prostate cancer risk.

Notably, a decrease in absolute CRF was correlated with a higher risk of prostate cancer diagnosis. This association remained significant after adjusting for all covariates, including physical activity.

Participants were also categorized by CRF change, which included increased, stable, or decreased +3%, ±3%, and −3%, respectively. Those with increased CRF had a significantly lower risk of cancer incidence as compared to the stable group, which remained consistent across most adjusted models.

A sensitivity analysis that excluded early diagnoses after the last test confirmed the significance of absolute CRF changes on cancer risk. However, significant variability across the different models was observed when comparing stable CRF to increased or decreased groups.

The subgroup analysis, which was stratified by baseline CRF levels, revealed that in the moderate baseline CRF group of 32.4-40.7 mL/kg/min, each standard deviation increase in absolute CRF reduced prostate cancer incidence risk by 16% in the least adjusted model, with significant associations persisting in more adjusted models. Comparatively, low and high fitness groups showed no significant associations, except for an inverse relationship in the high fitness group in the least adjusted model, which diminished upon further adjustments.

A positive correlation was also observed between changes in absolute CRF and self-reported physical activity. However, changes in CRF did not correlate with prostate cancer mortality, as evidenced by the 46 observed deaths in the study.