Irritable bowel syndrome (IBS) is one of the most common gastrointestinal disorders. Pooled population surveys put its global prevalence at about 11%, close to 1 in 10 people.
How common IBS is
Estimates vary widely. Population surveys report prevalence figures from 1.1% to 45%, and when many studies are pooled the global figure is about 11%; most European countries, the United States and China fall between 5% and 10%. The spread has a clear cause: studies that use the older Rome III criteria count more cases than those using Rome IV, which demands more frequent pain, and differences in how a survey recruits and questions people add to the variation. Two estimates that disagree can therefore both be right for their own definition.
IBS is common in clinics as well as in the community. People with IBS account for a substantial share of gastrointestinal consultations, but only about half of those with IBS-like symptoms ever seek medical care, and only a minority are referred to a specialist; the rest manage the symptoms themselves.
Who is affected
IBS is more common in women and in younger adults. Across population studies, female sex carries an odds ratio of about 1.67, so women are roughly 67% more likely than men to develop IBS. The pattern is not uniform worldwide: women outnumber men in the United States, while in some Asian countries men outnumber women. The bowel pattern differs by sex too, with women tending towards IBS-C and men towards IBS-D.
Age is less straightforward than it first appears. IBS becomes less common as people get older, yet it does not disappear: some studies find a higher prevalence over 85 years than over 65, which may reflect under-diagnosis or misdiagnosis in older people rather than a real rise.
Natural history and prognosis
IBS is chronic and relapsing rather than progressive. New cases appear at roughly 1–2% a year and symptoms disappear at a similar rate, so the overall prevalence stays fairly stable even though individual patients change. A substantial proportion of patients have a spontaneous remission over time, but no treatment cures the disorder, and symptoms commonly recur.
When IBS symptoms do resolve they are often replaced by another functional gastrointestinal disorder; about half of patients whose IBS remits go on to develop one. Because symptoms fluctuate, the predominant subtype can change from one period to another.
The effect on quality of life is substantial, comparable to that of other chronic diseases, and it comes as much from extra-intestinal complaints — fatigue, poor sleep, anxiety and a general sense of being unwell — as from bowel symptoms.