Background: Although Helicobacter pylori infection is a major risk factor for gastric cancer, it does not explain the full picture of stomach carcinogenesis. There have been few epidemiological studies, however, which examined both H. pylori and environmental factors simultaneously. The aims of this study were to estimate the association of environmental factors (smoking and dietary factors) with gastric cancer in consideration of H. pylori infection, and to investigate the effects of the interaction between environmental factors and H. pylori infection.
Methods: A multicenter, hospital-based, case-control study of gastric cancer was conducted at four hospitals in Nagano prefecture, Japan, between October 1998 and March 2002. For 153 newly diagnosed gastric cancer cases, two controls matched by age (within 3 years), sex, and residence area were randomly selected from the participants of a health check-up program during the same period in the same hospitals. We conducted a questionnaire survey and obtained blood samples. Consequently, 122 non-cardia gastric cancer cases and 235 controls were available for this analysis.
Results: Results. H. pylori infection was strongly associated with non-cardia gastric cancer after adjustment for possible confounding factors (odds ratio [OR], 8.2; 95% confidence interval [CI], 3.7-18.2). Cigarette smoking (OR, 2.8; 95% CI, 1.2-6.5) and frequent intake of miso (fermented soy bean) soup (OR, 2.1; 95% CI, 0.9-5.1) and rice (OR, 2.5; 95% CI, 1.0-6.1) were determined to be risk factors even after adjusting for possible confounding factors, including H. pylori infection. However, no statistically significant interaction between environmental factors and H. pylori infection was detected.
Conclusion: This finding suggests that although H. pylori infection is clearly an important risk factor for gastric cancer, smoking cessation and dietary modification may be practical strategies for the prevention of non-cardia gastric cancer among both H. pylori-positive and -negative subjects in Japan.