Ready for another reason to exercise? Men who exercise at even moderate levels may have a lower risk of prostate cancer than sedentary men, a new study suggests. Exercise has been shown to have numerous health benefits, but studies have come to conflicting conclusions as to whether a lower risk of prostate cancer is one of them. In this latest study, researchers found that among 190 men who underwent biopsies to detect possible prostate cancer, those who regularly exercised were less likely to be diagnosed with the disease. Men who exercised moderately -- the equivalent of three or more hours of brisk walking per week -- were two-thirds less likely than their sedentary counterparts to have prostate cancer. What's more, among men who did have cancer, those who reported as little as one hour of walking per week were less likely to have aggressive, faster-growing cancer. Dr. Jodi A. Antonelli and colleagues at Duke University Medical Center in Durham, North Carolina, report the findings in the Journal of Urology. There are a number of reasons to believe that exercise could help ward off prostate cancer. For one, physical activity tends to lower levels of testosterone and other hormones that help feed prostate tumor growth. Exercise may also bolster the immune system, which, by killing off abnormal cells before tumors can develop, is one of the body's lines of defense against cancer.