Green tea consumption and stomach cancer risk: a meta-analysis

Abstract

Objectives: Green tea has been suggested to have a chemopreventive effect against various cancers including stomach cancer. The aim of this study is to elucidate the relationship between green tea consumption and stomach cancer risk by meta-analysis.

Methods: Eighteen observational studies were identified using MEDLINE, THE COCHRANE LIBRARY, RISS, and a manual search. Summary relative risks/odds ratios (RR/ORs) for the highest versus non/lowest green tea consumption levels were calculated on the basis of fixed and random effect models. Subgroup analyses were used to examine heterogeneity across the studies.

Results: The combined results indicate a reduced risk of stomach cancer with intake of green tea (RR/OR=0.86, 95% CI=0.74-1.00). Subgroup analysis with six studies that reported differences between the highest and lowest consumption levels equal to or greater than five cups/day revealed a statistically significant protective effect (RR/OR=0.68, 95% CI=0.53-0.87).

Conclusion: Green tea appears to play a protective role against the development of stomach cancer. The results also suggest that a higher level of green tea consumption might be needed for a clear preventive effect to appear. This conclusion, however, should be interpreted with caution because various biases can affect the results of a meta-analysis.

Keywords: Green tea; Meta-analysis; Stomach cancer.

Figure 1

Flow of study selection process.

Figure 2

Forest plot of relative risks or odds ratios from eighteen observational studies on green tea consumption and stomach cancer. The black squares and horizontal lines correspond to the RRs or ORs and 95% confidence intervals. The area of the black squares reflects the weight each trial contributes to the meta-analysis. The diamond at the bottom of the graph represents the combined odds ratio and its 95% confidence interval, indicating 14% reduction in the risk of stomach cancer. The solid vertical line corresponds to no effect of green tea consumption (odds ratio 1.0), the dotted vertical line to the combined odds ratio (0.86). The graph was produced in STATA.

Figure 3

Begg's funnel plot of studies on green tea consumption and stomach cancer risk. The solid line in the center is the natural logarithm of pooled odds ratio (OR), and two oblique lines are pseudo 95% confidence limits. SE, standard error.