In a review conducted at the Mayo Clinic, published in the American Journal of Gastroenterology, authors identified the prevalence of IBS in North America as ranging from 3- 20%, with most prevalence estimates ranging from 10-15%. Interestingly, prevalence of diarrhea-predominant (IBS-D) and constipation-predominant (IBS-C) were each shown as approximately 5%. Published prevalence estimates by gender range from 2:1 female predominance to a ratio of 1:1. IBS-C is more common in females. The prevalence of IBS varies minimally with age. The authors did not find any true population-based incidence studies or natural history studies. In one cohort, surveyed on two occasions one year apart, 9% of subjects who were free of IBS at baseline reported IBS at follow-up producing an onset rate of 67 per 1000 person-years. In all, 38% of patients meeting criteria for IBS did not meet IBS criteria at the one-year follow-up survey.
In summary, approximately 30 million people in North America meet the diagnostic criteria for IBS. However, data about the natural history of IBS is quite sparse. The study authors suggest that researchers should focus renewed efforts toward developing appropriately designed trials to reveal the true epidemiology of IBS.