Drinking five cups a day lowered risk by 48% compared with drinking less than one cup a day.
Green tea may be associated with a decreased risk of advanced prostate cancer, according to researchers in Tokyo.
In a prospective study by investigators at Japan’s National Cancer Center, men who drank five or more cups of green tea a day had a 48% reduced risk of advanced prostate cancer compared with men who drank less than one cup a day, after adjusting for multiple potential confounders, the investigators reported in the American Journal of Epidemiology (2007;167:71-77). The researchers, led by Norie Kurahashi, MD, observed no association between green tea consumption and localized prostate cancer.
Dr. Kurahashi’s team analyzed data from 49,920 men, including 404 with newly diagnosed prostate cancer, who were enrolled in the Japan Public Health Center-based Prospective Study. The new findings are consistent with those of some previous studies, but not others. For example, a case-control study in southeast China found that the risk of the malignancy decreased with increasing frequency of green tea consumption (Int J Cancer. 2004;108:130-135).
A case-control study in Canada found that general tea consumption was associated with a decreased risk of prostate cancer (Int J Cancer. 1998;78:707-711). But another Canadian study (Cancer Causes Control. 1999;10:355-367) and an Italian study (Nutr Cancer. 1992;17:27-31) found no difference in prostate cancer risk between general tea drinkers and nondrinkers.
Dr. Kurahashi and colleagues noted that subjects in some of these previous studies did not commonly drink green tea, but black tea. They also pointed out that almost all of the previous studies did not consider the effect of tea according to cancer stage.
The authors noted that the study’s prospective design was among its strengths. Collecting green tea consumption data prior to subsequent diagnosis of prostate cancer allowed them to avoid recall bias. Another strength was the high response rate (about 80%) and negligible loss to follow-up (0.2%).
One of the study’s limitations was the absence of data on whether men had been screened for prostate cancer. “It is possible that men who have health check-ups are more health conscious and may drink more green tea, which would attenuate the results for localized prostate cancer and obscure any preventive effects on localized prostate cancer.”