A PROSPECTIVE-STUDY OF PHYSICAL-ACTIVITY AND PROSTATE-CANCER IN MALE HEALTH-PROFESSIONALS

Because the role of exercise in prostate cancer is unclear, we examine d the relationship between leisure time physical activity and risk of prostate cancer in the Health Professionals Follow-up Study, a prospec tive cohort study of male health professionals in the United States. I n 1986, 47,542 men 40-75 years of age and free of cancer responded to a mailed questionnaire that included an assessment of physical activit y. The reported average time per week spent on each of a variety of no noccupational activities was multiplied by its typical energy expendit ure requirements expressed in metabolic equivalents (METs) and summed to yield a total weekly MET-hour score. We also examined MET-hours fro m all vigorous activities, defined as those requiring energy expenditu res of six or more METs, and nonvigorous activities. From 1986 until J anuary 31, 1994, we identified 1362 incident cases of total prostate c ancer (excluding stage Al), 419 advanced (extraprostatic) cases, and 2 00 metastatic cases. No relationship with total or advanced prostate c ancer was evident for total, vigorous, and nonvigorous physical activi ty. For metastatic prostate cancer, we also found no linear trends for these activities, but did observe a significantly lower risk in the h ighest category of vigorous activity (multivariate relative risk = 0.4 6; 95% confidence interval = 0.24-0.89 for >25 versus 0 MET-hours), co ntrolling for age, vasectomy, history of diabetes, height, smoking, an d dietary factors. This highest category included 15% of the populatio n and reflects at least 3 h/week of participation in vigorous activiti es. Differences in disease surveillance according to activity level co uld not account for our findings. The results from this cohort indicat e that physical activity is unlikely to influence the incidence of tot al prostate cancer appreciably; however, the suggestion of a lower ris k of metastatic prostate cancer in men engaging in high levels of vigo rous activities warrants further study.