Consumption of fruit, but not vegetables, may reduce risk of gastric cancer: Results from a meta-analysis of cohort studies
Introduction
Worldwide, gastric cancer (GC) remains the second leading cause of death due to cancer, although both the incidence and mortality rates of gastric cancer have been on the decline for the past century [1], [2]. Infection with Helicobacter pylori has been recognised as the strongest risk factor for gastric cancer [3] and may even be a (close to) necessary condition for the development of gastric non-cardia adenocarcinoma (GNCA) [4]. Epidemiological studies have suggested that dietary factors play an important role in the aetiology of GC, but the specific dietary components involved remain unclear, except for the consumption of salt and salt-preserved foods [5], [6], and alcohol abuse [7].
The consumption of vegetables and fruit has long been of interest for their possible favourable effect on risk of cancers. These foods contain many substances, such as vitamin C, vitamin E, folate, carotenoids and flavonoids, which are believed to prevent the formation of nitrosamines and neutralise the action of preformed nitrosamides, modulate DNA methylation, induce detoxifying phase II enzymes and promote apoptosis [8], [9]. Based on a narrative review in 2007, the Working Group from the World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) reported that although a significant decreased risk for total vegetables and fruit was observed in case-control studies, a non-significant decreased risk was observed in cohort studies [10]. Case-control studies are more subject to recall and selection bias compared to cohort studies because of their retrospective nature, which can be of importance when investigating diet and gastrointestinal cancer. Thus, the Working Group concluded that high consumption of vegetables and fruit ‘probably’ protects against the development of gastric cancer [11].
Since this article’s publication, a lot of prospective cohort analyses of fruit and vegetable consumption and gastric cancer risk have been published with mixed results [12], [13], [14], [15], [16], [17], [18], [19]. Therefore, to better characterise this issue, we conducted a comprehensive meta-analysis of cohort studies by using our own methods and criteria. Furthermore, we evaluated the risk associations according to sex, gastric cancer subtypes (gastric cardia adenocarcinoma [GCA] and GNCA), study quality score, outcome, duration of follow-up and important confounding factors. We also examined the shape of the dose–response relationship (i.e. whether there are any threshold effects) by conducting non-linear dose–response analyses.
Section snippets
Literature search
This meta-analysis was planned, conducted and reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement [20]. Two investigators (C.Y. and W.Q.B.) sought to identify all epidemiologic studies by searching MEDLINE and EMBASE through August 2013 and by hand-searching the reference list of the computer retrieved articles. We searched for relevant studies with the following text words and/or Medical Subject Heading terms: (1) gastric OR stomach
Search results, characteristics and quality assessment
We identified and screened 5319 potentially relevant references, and 5194 were excluded on the basis of title and abstract. The remaining 125 articles were retrieved for more detailed assessment. One hundred and nine articles were excluded after further evaluation because they had study designs other than cohort, no data presented the association of interests, and reported several cancer sites combined or reported the same cohorts. Scanning reference lists and personal databases identified one
Discussion
Results of this meta-analysis indicate that consumption of fruit, but not vegetables, was inversely associated with GC risk. The risk decrease in consumption of fruit was 10% in high versus low analysis, and 5% per 100-g/day increment in fruit consumption. We found for the first time, to our knowledge, evidence of a non-linear inverse association between fruit and GC risk, with the greatest reduction in risk at the lower range (∼100 g/day) of fruit intake.
We observed non-significant inverse
Conflict of interest statement
None declared.
Acknowledgements
Qingbing Wang, Yi Chen and Xiaolin Wang participated in the design of this manuscript. Qingbing Wang, Yi Chen and Gaoquan Gong participated in abstracting the data. Yi Chen, Guoping Li and Changyu Li performed statistical analysis and manuscript preparation. All authors read and approved the final manuscript.
References (58)
- et al.
Natural history of Helicobacter pylori infection
Dig Liver Dis
(2008) - et al.
A meta-analysis on alcohol drinking and gastric cancer risk
Ann Oncol
(2012) - et al.
Epidemiologic evidence of the protective effect of fruit and vegetables on cancer risk
Am J Clin Nutr
(2003) - et al.
Dietary factors and cancer mortality among atomic-bomb survivors
Mutat Res
(2004) - et al.
Meta-analysis in clinical trials
Control Clin Trials
(1986) - et al.
EUROCARE-4. Survival of cancer patients diagnosed in 1995–1999. Results and commentary
Eur J Cancer
(2009) - et al.
Recent trends of cancer in Europe: a combined approach of incidence, survival and mortality for 17 cancer sites since the 1990s
Eur J Cancer
(2008) Dietary assessment and the reliability of nutritional epidemiology reports
Lancet
(2003)- et al.
Fruit and vegetable intake and risk of cancer: a prospective cohort study
Am J Clin Nutr
(2009) - et al.
Fruit, vegetables, and colorectal cancer risk: the European Prospective Investigation into Cancer and Nutrition
Am J Clin Nutr
(2009)