Association of tea consumption and the risk of oral cancer: A meta-analysis
Introduction
Oral cavity cancer, comprising cancer of tongue, buccal mucosa, upper or lower gingival, floor of mouth and hard palate, represents the eighth most frequent cancer worldwide [1]. In China, it was reported that the incidence rate and mortality rate of oral cavity cancer were 3.29 per 100,000 and 1.49 per 100,000 in 2008 [2]. Oral cancer is a serious problem in many parts of the world [3], mainly due to its low survival rate [4] and poor life quality [5], [6], especially for advanced oral cancer cases. Thus, primary prevention is important. Many studies have shown that oral cancer is associated with genetic factors [7], [8], [9]. Furthermore, many environmental factors such as tobacco smoking [10], alcohol drinking [11], fruit and vegetables [12] can also affect the incidence of oral cancer.
Tea, which is derived from the leaves of the plant Camellia sinensis, is one of the most popular beverages consumed worldwide, and generally the most consumed are black tea and green tea. Evidence from laboratory studies strongly showed the inhibition of tumorigenesis by tea and its constituents [13], [14]. Up to date, a number of epidemiologic studies have been published to explore the relationship between tea consumption and oral cancer risk. However, the results are not consistent. Therefore, we conducted a meta-analysis to (1) first assess the oral cancer risk for the highest vs. lowest categories of tea consumption; (2) assess the heterogeneity among studies and publication bias.
Section snippets
Search strategy
We performed a literature search up to June 2013 using the databases of PubMed, Web of Knowledge and Wan Fang Med Online. The following search terms were used: ‘tea’ and ‘oral cancer’ without restrictions. Moreover, we reviewed the reference lists from retrieved articles to search for further relevant studies. Two investigators searched articles and reviewed of all retrieved studies independently. Disagreements between the two investigators were resolved by consensus with a third reviewer.
Inclusion criteria
All
Characteristics of studies
The search strategy identified 343 articles from PubMed, 595 articles from the Web of Knowledge and 24 articles from Wan Fang Med Online. 30 articles were reviewed in full after reviewing the title/abstract. One article reported the upper aerodigestive tract cancer with tea consumption and one article reported the coffee and tea consumption with the risk of oral cancer. 12 articles were review. Two articles that did not report the risk estimate were also excluded. Finally, 14 articles [20], [21]
Discussion
The findings from this meta-analysis indicated that highest tea consumption level versus lowest level was significantly associated with the risk of oral cancer. An inverse association was also found in green tea consumption but not in the black tea consumption. The associations were significant between tea consumption and oral cancer in Asian and Caucasian. As three studies were carried out from Brazil with mixed ethnic background, we pooled the result for Brazil only. And no significant
Conflict of interest statement
None declared.
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