OBJECTIVES: Irritable bowel syndrome (IBS) is considered to be a transcultural functional bowel disorder with high comorbidity and psychiatric disorders; but well-designed epidemiologic studies have never been performed in Japan. The purpose of this study was to establish the prevalence of IBS, together with the comorbidity rates of panic disorder (PD) and agoraphobia, employing a large-scale survey based on stratified random sampling. METHOD: A total of 4,000 subjects aged 20-69 years completed a questionnaire and the results were weighted to ensure representativeness of the Japanese general population. The questionnaire covered key symptoms of IBS, PD, and agoraphobia. The prevalence of IBS and its subtypes was calculated by gender. The comorbidity of PD and agoraphobia with IBS was compared with morbidity in non-IBS subjects; and comorbidity in IBS subjects who had consulted medical practitioners regarding their symptoms and in those who had not was also compared. RESULTS: The prevalence of IBS was 6.1% in total. It was significantly higher in females than in males. Diarrhea-predominant IBS was more prevalent in males and constipation-predominant IBS in females. The morbidity rates of PD and agoraphobia were significantly higher in IBS than in non-IBS subjects. Comorbidity did not differ between female and male IBS subjects, while morbidity was significantly higher in female than in male non-IBS subjects; and comorbidity did not differ between consulter and nonconsulter subjects. CONCLUSIONS: The prevalence of IBS and its comorbidity with PD and agoraphobia in Japan were demonstrated to be similar to those reported in Western industrialized countries.
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