Men who drink six cups of coffee a day showed a lower risk of developing a deadly type of prostate cancer compared with nondrinkers, a large U.S. study suggests.

The study by researchers at the Harvard School of Public Health compared risk of aggressive prostate cancer among 47,911 U.S. men in the Health Professionals Follow-Up Study. Participants reported their coffee consumption every four years from 1986 to 2008.

Men who consumed coffee regularly had a reduced risk of lethal or advanced prostate cancer, a study of health professionals found. Adeel Halim/Reuters

During the study period, 5,035 cases of prostate cancer were reported, including 642 fatal or metastatic cases, Lorelei Mucci, an associate professor of epidemiology at Harvard and her co-authors reported in Tuesday's online issue of the Journal of the National Cancer Institute.

"In conclusion, men who consumed coffee regularly had a reduced risk of lethal or advanced prostate cancer," the study's authors wrote.

"It is premature to recommend that men increase coffee intake to reduce advanced prostate cancer risk based on this single study. In addition, the effects of coffee consumption on other aspects of health must be considered in making consumption recommendations."

If the findings are confirmed, coffee could offer a way to lower the risk of developing of prostate cancer, the researchers added.

The results included:

• Men who consumed the most coffee — six or more cups daily — had 0.82 times the risk of developing any form of prostate cancer.
• Men who drank the most coffee had a 0.40 times lower risk of developing lethal prostate cancer.
• The reduction in risk occurred whether men drank decaffeinated or regular coffee, and does not appear to be due to caffeine.
• Coffee drinkers were more likely to smoke and less likely to exercise, lifestyle factors that were taken into account in estimating the risk reduction from the drink.

The link between drinking coffee and lower risk of advanced prostate cancer is biologically plausible, the researchers said. Coffee contains many beneficial compounds with antioxidant and anti-inflammatory effects and affect sex hormone levels, all of which they said may influence prostate cancer.

Mucci's team is planning more research to understand specifically how coffee lowers the risk of lethal prostate cancer.

The study was funded by the U.S. National Cancer Institute, American Institute for Cancer Research and Prostate Cancer Foundation.