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A moderate amount of exercise most days of the week may contribute to a lower risk of prostate cancer, and lower grade tumors among those men who are diagnosed with the disease following biopsy, say researchers at Duke University Medical Center and the Durham Veterans Affairs Hospital.

The finding, appearing online in the Journal of Urology, adds more fuel to the ongoing debate over whether exercise offers any benefit at all among men seeking to prevent prostate cancer. 

"There have been dozens of studies about the value of exercise in lowering risk of prostate cancer, and some of them quite large, but the bottom line is that they've left us with mixed signals," says Stephen Freedland, MD, a urologist at Duke and the Durham VA and the senior author of the paper. 

In examining 190 men who underwent prostate biopsy at the Durham Veterans Affairs Medical Center, investigators found that men who regularly engaged in moderate activity -- anything equivalent to walking at a moderate pace for several hours per week -- were significantly less likely to be diagnosed with prostate cancer, and if they were, they were less likely to have aggressive disease, defined as a tumor with a Gleason score equal to or greater than 7.

They assessed participants' level of exercise with a questionnaire prior to the biopsy.

The survey included questions about the frequency, duration and intensity of any exercise during a typical week. The type of activity was designated either mild (easy walking, yoga), moderate (brisk walking, tennis), or strenuous (running, vigorous swimming).

Most of the men fell far short of the American Heart Association guidelines for the minimal amount of exercise needed per week. Researchers found that a majority of the men (58 percent) were sedentary, meaning they exercised less than the equivalent of one hour per week of easy walking. Forty-six percent were moderately active; only 33 percent were very active.

After adjusting for age, race, weight, PSA score, family history of the disease, and other variables, investigators found that men who reported more hours per week of exercise were significantly less likely to have cancer on biopsy.

But investigators found that any amount of exercise was associated with a trend toward a lower risk of prostate cancer.

"As the amount of exercise increased, the risk of cancer decreased," says Jodi Antonelli, MD, a urology resident at Duke and the lead author of the study. Among men who were found to have cancer, even exercising as little as one hour per week of easy walking was associated with a lower risk of high-grade disease.

While the results point to a relationship between exercise and prostate cancer risk, Antonelli says they should be interpreted with caution.

"This is a relatively small study -- and it is not a screening study -- so it may not be appropriate to apply our results to a general population. In addition, it is impossible to state that exercise alone was responsible for the benefits we observed because participants who exercised might also have engaged in other behaviors linked to better health, like adhering to good diet. That means we can not clearly identify a causal relationship."

Funding for the study came from the Department of Veterans Affairs, Department of Defense, and the American Urology Association Foundation Astellas Rising Star in Urology Award.

Co-authors from Duke and the Durham VA include Lee Jones, Lionel Banez, Jean-Alfred Thomas, Kelly Anderson, Loretta Taylor, Leah Gerber, Catherine Hoyo and Tiffany Anderson; and Delores Grant, from North Carolina Central University.