Green tea and incidence of colorectal cancer: evidence from prospective cohort studies.

A systematic meta-analysis of prospective cohort studies on green tea consumption and colorectal cancer was performed to determine whether green tea has a chemopreventive effect against colorectal cancer. Six eligible cohort studies involving 352,275 participants and 1675 cases of colorectal cancer were identified. Combined relative risk (RR) ratios for the highest vs. lowest and increment of 1 cup/day green tea consumption levels were calculated. The combined RR of 0.90 (95% CI: 0.72-1.08) was found comparing highest vs. lowest green tea consumption levels for colorectal cancer. No significant differences by cancer-site were found, but an inverse association between green tea and incidence of colorectal cancer (RR: 0.70; 95% CI: 0.55-0.85) and colon cancer (RR: 0.69; 95% CI: 0.48-0.98) was demonstrated in Shanghai population. Singapore men had a higher risk of colorectal cancer (RR: 1.36; 95% CI: 1.06-1.74). Furthermore, an increase in green tea consumption of 1 cup/day was not associated with incidence of colorectal cancer (RR: 0.97; 95% CI: 0.91-1.03). Despite the limited evidence from Shanghai studies in support of green tea as potential chemopreventive agents against colorectal cancer, available data from prospective cohort studies are insufficient to conclude that green tea may protect against colorectal cancer.