Sun Can-Lan, Yuan Jian-Min, Koh Woon-Puay, Yu Mimi C
The Cancer Center, University of Minnesota, Minneapolis, MN 55455, USA.
Carcinogenesis. 2006 Jul;27(7):1301-9. doi: 10.1093/carcin/bgl024. Epub 2006 Apr 25.
Experimental studies have supported tea as a chemopreventive agent for colorectal cancer. No quantitative summary of the epidemiologic evidence on tea and colorectal cancer risk has ever been performed. The current meta-analysis included 25 papers conducted in 11 countries across three continents (North America, Asia and Europe). Summary odds ratios (ORs) for highest versus non/lowest tea consumption levels were calculated based on fixed and random effects models. The meta-regression and stratified methods were used to examine heterogeneity across studies. For green tea, the combined results from eight studies indicated a reduced risk of colorectal cancer with intake [summary OR = 0.82, 95% confidence interval (CI) = 0.69-0.98]. The protective effect is mainly found among the three case-control studies of colon cancer (summary OR = 0.74, 95% CI = 0.60-0.93). Results from studies of rectal cancer irrespective of study design (case-control versus cohort) (summary OR = 0.99, 95% CI = 0.71-1.37) and cohort studies of colon cancer (summary OR = 0.99, 95% CI = 0.79-1.24) were compatible with the null hypothesis. For black tea, the summary OR derived from 20 studies was 0.99 (95% CI = 0.87-1.13). There is wide divergence in results across the 20 individual studies; formal tests for homogeneity across studies revealed statistically significant differences in findings across all studies (P < 0.001), amongst the 7 cohort studies (P = 0.002), and amongst the 13 case-control studies (P < 0.001). Despite the strong evidence from in vitro and non-human in vivo studies in support of green and black tea as potential chemopreventive agents against colorectal cancer, available epidemiologic data are insufficient to conclude that either tea type may protect against colorectal cancer in humans.
实验研究支持茶作为结直肠癌的化学预防剂。此前从未对茶与结直肠癌风险的流行病学证据进行过定量总结。当前的荟萃分析纳入了在三大洲（北美、亚洲和欧洲）11个国家开展的25篇论文。基于固定效应模型和随机效应模型计算了最高茶摄入量与非/最低茶摄入量水平的汇总比值比（OR）。采用元回归和分层方法检验各研究间的异质性。对于绿茶，八项研究的综合结果表明，摄入绿茶可降低患结直肠癌的风险[汇总OR = 0.82，95%置信区间（CI）= 0.69 - 0.98]。这种保护作用主要在三项结肠癌病例对照研究中发现（汇总OR = 0.74，95% CI = 0.60 - 0.93）。无论研究设计如何（病例对照研究与队列研究），直肠癌研究的结果（汇总OR = 0.99，95% CI = 0.71 - 1.37）以及结肠癌队列研究的结果（汇总OR = 0.99，95% CI = 0.79 - 1.24）均与零假设相符。对于红茶，20项研究得出的汇总OR为0.99（95% CI = 0.87 - 1.13）。20项独立研究的结果存在很大差异；对所有研究进行的同质性正式检验显示，各研究结果存在统计学显著差异（P < 0.001），在7项队列研究中（P = 0.002）以及在13项病例对照研究中（P < 0.001）也是如此。尽管体外和非人体体内研究有强有力的证据支持绿茶和红茶作为预防结直肠癌的潜在化学预防剂，但现有的流行病学数据不足以得出这两种茶能预防人类结直肠癌的结论。
