No Definitive Link Found Between Physical Activity and Prostate Cancer

A large meta-analysis was unable to find a conclusive relationship between levels of physical activity and the risk of prostate cancer, though some suggestion of reduced risk was seen for occupational activity and for some specific cancer subtypes. There was also indication that physical activity after diagnosis of prostate cancer might have a protective effect.

“Knowledge about risk factors of prostate cancer is limited, complicating the formulation of appropriate strategies for the prevention of prostate cancer,” wrote study authors led by Daniela Schmid, MSc, of the University of Regensburg in Germany. “The role of potential modifiable risk factors for the development of prostate cancer such as obesity, smoking, poor diet, and physical activity is less well understood.”

The authors conducted a meta-analysis and review of studies of physical activity and prostate cancer, including 48 cohort studies and 24 case-control studies incorporating a total of 151,748 cases of prostate cancer. The mean age of the study participants at baseline was 61 years. Results were published in Annals of Oncology.

The primary analysis relating physical activity to prostate cancer revealed an association that was close to null, with a relative risk (RR) of 0.99 (95% CI, 0.94–1.04) comparing the highest and lowest categories of activity. The same held true when the case-control and the cohort studies were examined separately.

They then stratified by the domain of physical activity, and found a significant inverse association between long-term occupational activity and total prostate cancer incidence, with an RR of 0.83 (95% CI, 0.71–0.98) and a borderline association with short-term occupational physical activity with an RR of 0.85 (95% CI, 0.72–1.00). However, the long-term significant RR did not remain significant after removal of individual studies from the analysis.

When stratifying by both type of physical activity and subtypes of prostate cancer, further associations were seen. There was an inverse association between long-term recreational physical activity and advanced/aggressive prostate cancer, with an RR of 0.75 (95% CI, 0.60–0.95), though this incorporated only 2 studies. There was also an inverse association between long-term occupational physical activity and non-advanced/non-aggressive prostate cancer, with an RR of 0.51 (95% CI, 0.37–0.71), again with 2 studies.

There was no association seen between pre-diagnosis physical activity and mortality due to prostate cancer. However, there was an inverse association between physical activity after diagnosis and prostate cancer mortality among survivors, with an RR of 0.69 (95% CI, 0.55–0.85), based on 4 studies.

“These associations may represent an indication for a potential protective effect of long-term activity on prostate cancer incidence,” the authors wrote. “However, our findings must be interpreted with caution.” The analysis’s sensitivity to removal of individual studies, and the small number of studies that revealed some of the significant results, make interpretation difficult. “Despite a growing body of literature on physical activity and prostate cancer incidence, evidence for a link between overall physical activity and risk of prostate cancer remains elusive.”