Epidemiology of Functional Gastrointestinal Disorders in Japan and in the World

Functional gastrointestinal disorders (FGIDs), represented by functional dyspepsia (FD) and irritable bowel syndrome (IBS), are a group of disorders that include variable combinations of chronic or recurrent gastrointestinal symptoms not explained by structural or biochemical abnormalities. FGIDs account for a significant percentage of patients seen in primary care settings with abdominal symptoms. Although the definition of FGIDs can easily affect the prevalence, the prevalences of dyspepsia/FD and IBS diagnosed by the Rome III criteria in the general population are 5.3–20.4% and 1.1–29.2%, respectively. Recent reports of FD and IBS defined by the Rome III criteria indicated a female predominance. Regarding the subtype prevalence of FD, postprandial distress syndrome was more prevalent than epigastric pain syndrome (5.6–13.9% vs 0.9–9.5%). The subtype prevalence of IBS is characterized by male predominance for IBS with diarrhea and female predominance for IBS with constipation. Factors affecting the development of FGIDs such as epidemiological factors including genetic and environmental factors, are important. Gene polymorphisms are involved in the development of FGIDs. The prevalence differs among races and geographic areas. Foods may affect the development of FGIDs, but the causal relationships between food and FGIDs are not conclusive. The symptoms often regress and appear in the course of these entities. Building a favorable patient-doctor relationship is effective for controlling symptoms of FGIDs. Physicians should explain that FGIDs are highly prevalent conditions, impair the patients’ quality of life even without evident underlying organic causes and are not life-threatening conditions to ensure patients’ understanding.