The epidemiology of IBD worldwide

Abstract

In the western world a sharp rise in the incidence of inflammatory bowel disease (IBD) has been observed since the early 1950s. The increase in the incidence of ulcerative colitis preceded the increase in the incidence of Crohn’s disease by about 10-15 yr. In high incidence areas, a female preponderance at a young age is observed in Crohn’s disease, whereas in ulcerative colitis male incidence is still high at older ages. IBD is more common in the western world than in eastern areas and, in both the United States and Europe, a north-south gradient has been reported, with IBD more common in the north than in the south. There are also indications that in typically low incidence areas, more cases are being seen lately. Rates for Japan suggest that this Asian population is now affected with approximately equal frequency as western populations with regard to ulcerative colitis; Crohn’s disease in contrast is still less common. The prevalence of Crohn’s disease in the Chinese populations in Hong Kong and Singapore appears to be increasing, and more cases have also been observed lately in central China. This could be due to a greater awareness and better availability of health care and/or improved study methods. However, it may also be a real increase, reflecting changing environmental factors. Both genetic factors and environment are thought to be important in developing IBD, the observed increase during the past decennia is probably due to environmental factors since genetic make-up cannot change that quickly. Smoking is the only consistent risk factor in case-control studies, but does not seem to explain the observed changes in incidence and age and gender distribution in the two diseases, nutrition and life-style factors changed to a great extent during the period in which the rising incidence of IBD has been reported. Following the temporal trends in these areas and using case-control settings in a population based manner during the coming years should prove to be of great interest, as this might shed some light on the role of environmental factors in the etiology of IBD.

Key Words: Inflammatory bowel disease; Crohn’s disease; Ulcerative colitis; Environmental factors; Genetic factors