A research team from Japan's health ministry surveyed 49,920 men aged 40-69 across the nation in 1990 and 1993 and followed up on their health until 2004, the National Cancer Centre said.
During this time, 404 men were newly diagnosed with prostate cancer, of whom 114 had advanced cases, 271 were localised, and 19 were of an undetermined stage.
An analysis found the risks of having advanced prostate cancer was 50 percent lower for men who drink five or more cups of green tea a day compared with those who have less than one cup, the study said.
Tea curbs testosterone levels
"Green tea was not associated with localised prostate cancer," the research group said in a report.
But it added: "Green tea may be associated with a decreased risk of advanced prostate cancer."
The research team said a substance called catechin in green tea may be contributing to reducing risks by curbing levels of testosterone, a male hormone seen as a risk factor to prostate cancer.
The incidence of prostate cancer is much lower in Asian than Western populations. The study began on the assumption that this may be linked to the high consumption of green tea in Asian populations.
The findings were published in the online version of the American Journal of Epidemiology. – (Sapa)