A review of physical activity and prostate cancer risk.

OBJECTIVES: The purpose was to review the etiologic role and the possible biologic mechanisms for physical activity in the primary prevention of prostate cancer and to identify future research priorities.
METHODS: We conducted literature searches and systematically reviewed all the epidemiologic studies of physical activity and prostate cancer and the literature on the underlying biologic mechanisms.
RESULTS: Among 24 previously conducted studies, 14 studies suggested an inverse association of physical activity on prostate cancer; however, no overall association was found in six studies and an increased risk of prostate cancer was observed amongst the most physically active men in four other studies. The methodologic limitations in these studies include variations in detection of latent disease and possible outcome misclassification, crude assessments of physical activity, inadequate control for confounding, and incomplete examination of effect modification.
CONCLUSIONS: Physical activity may have an inverse association with prostate cancer risk; however, the epidemiologic evidence is currently inconsistent and the magnitude of the risk reduction observed is small. These inconsistent results could be attributable, in part, to methodologic limitations of previous studies. Hence, further investigation of the etiologic role of physical activity is needed before more definitive conclusions can be made. Specifically, research studies should be designed to measure all types and parameters of physical activity throughout lifetimes. Furthermore, a better understanding of the biologic mechanisms and etiologically relevant time periods in prostate carcinogenesis when physical activity may be operative is needed, so that these studies can be properly designed.