The role of tomato products and lycopene in the prevention of gastric cancer: A meta-analysis of epidemiologic studies
Introduction
Although the incidence of gastric cancer has fallen in most western countries, it remains the second most common cause of cancer-related death worldwide. It has been estimated that approximately 1 million patients are newly diagnosed with gastric cancer worldwide each year, which accounts for nearly 10% of all cancer deaths and claims approximately 700,000 lives annually [1], [2]. It may be owing to healthy lifestyles and to improvements in the three important risk factors: prevalence of smoking, poor diet, and infection caused by Helicobacter pylori [3], [4], [5], [6], [7], [8]. A report published in 2007 by the World Cancer Research Fund and the American Institute for Cancer Research on the relationship between diet and cancer suggested that the consumption of certain types of food may be directly related to the development of malignancy including gastric cancer [9].
A increasing evidence has shown that tomatoes and tomato products may decrease the risk of many human malignant tumor such as prostate, ovarian, pancreatic, bladder, breast and gastric cancer [10], [11], [12], [13], [14], [15]. Lycopene is thought to be the active component in tomatoes and tomato products that is responsible for various types of cancer risk reduction, it has been suggested that potent antioxidants, because they reduce oxidative damage, may thereby prevent chronic diseases such as cancer and cardiovascular disease [16], [17]. Although an association between tomatoes, tomato products or lycopene and gastric cancer risk is biologically plausible, epidemiologic studies on this relationship have yielded inconsistent results.
Since 1970s, many epidemiologic studies have been published from different countries reporting on the association between tomatoes, tomato products or lycopene and risk of gastric cancer, but their conclusions have been inconsistent. Therefore, we performed a systematic review and meta-analysis of cohort and case–control studies to summarize available evidence on this issue.
Section snippets
Search strategy
To identify epidemiologic studies of tomatoes, tomato products and lycopene and risk of gastric cancer, we systematically conducted a literature search MEDLINE from January 1966 to June 2012 and Embase for all relevant articles. We used the following medical subject heading terms and/or text words: “carotenoids”, “tomatoes”, “lycopene”, or “diet”, combined with “stomach cancer”, “stomach neoplasm”, “gastric cancer”, or “gastric neoplasm”. We also scanned the reference lists of all retrieved
Results
A total of 17 studies published from 1985 through 2011 were identified in this meta analysis [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38]. Of the 17 studies, 5 were population based case–control studies, 6 were hospital-based case–control studies, and 6 were cohort studies. Of these studies, 12 studies were conducted in Europe, two in America, one each in Japan, China, and Uruguay (Table 1, Table 2). Sample sizes ranged from 223 to 82141
Discussion
The important role played by diet in preventing cancer has received much attention in recent years [50], [51]. Findings of this meta-analysis using studies published in recent years support the negative relationship between tomato products consumption and risk of gastric cancer. Overall, an increase in tomato products consumption was associated with statistically significant 36% reduced risks of gastric cancer in the studies.
There was a statistically significant heterogeneity among the 11
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These authors contributed equally.