Exercise Reduces Prostate Cancer Risk: Only in White Men?

Nick Mulcahy

February 11, 2013

Exercise might reduce a man's risk of developing prostate cancer, according to a study published online February 11 in Cancer.

The study adds to the literature indicating that exercise is a "modifiable risk factor" for prostate cancer, say lead author Abhay A. Singh, MD, from the Duke Prostate Center in Durham, North Carolina, and colleagues. They explain that "the emerging overall picture suggests a protective relationship" between exercise and prostate cancer.

However, Dr. Singh and colleagues report that the benefit is limited to white men; it does not apply to black men.

This could be a contributing factor to the increased risk for prostate cancer and aggressive prostate cancer in black men. "Further studies are needed to investigate the mechanism behind this racial disparity," said senior author Lionel L. Bañez, MD, from the Durham Veterans Affairs Medical Center, in a press statement.

Same Amount of Exercise

The authors prospectively evaluated 307 men (164 white and 143 black) who were undergoing prostate biopsy at the Veterans Affairs Medical Center in Durham.

The men completed a survey that assessed their current exercise behavior; this was translated into metabolic equivalent (MET) hours/week.

White men who were moderately or highly active, exercising at least 9 MET hours/week, were less likely to have a positive biopsy result than all men who were sedentary or mildly active, exercising less than 9 MET hours/week (odds ratio, 0.47; 95% confidence interval, 0.22 - 0.99; P = .047).

However, there was no association between MET hours/week and the risk for prostate cancer in black men.

Notably, the black and white men averaged about the same amount of weekly exercise. This removes "an important source of bias," the authors point out.

Other studies have had "mixed results" with regard to racial differences, exercise, and prostate cancer risk, the authors note. This study is distinguished by its prospective nature.

Dr. Singh and colleagues explain that the men in their study were scheduled to undergo biopsy; in the majority of other studies, a case–control design was used to identify prostate cancer patients through registries.

Despite the study findings, it is not clear whether exercise benefit is truly limited to white men, they note.

They acknowledge that the study had limitations. It had a "small sample size," did not specify the type or intensity of exercise, and evaluated only current (not historic) exercise. Although the study controlled for a variety of factors (age, body mass index, digital rectal examination, previous biopsy, Charlson comorbidity score, and family history of prostate cancer), other confounders could exist, they explain. Therefore, results from a Veterans Affairs population might not apply to other populations.

Nevertheless, the authors believe their findings are significant. They call for more study: "Investigating race-specific mechanisms by which exercise modifies prostate cancer risk and why these mechanisms disfavor black men in particular are warranted."

The authors have disclosed no relevant financial relationships.

Cancer. Published online February 11, 2013. Abstract