People of Indian origin living in the United States have a greater than average risk for all types of inflammatory bowel diseases (IBD) than other American populations, researchers report in the April issue of Clinical Gastroenterology and Hepatology. East Asians and Hispanics have a lower risk, similar to that of the populations still living in their original countries.
The prevalence of IBD is high in some geographic areas, such as Northern Europe, and in some ethnic groups. It is believed to be low in Eastern and Southern Asia. In India, ulcerative colitis was believed to be rare, although its incidence has been increasing and approaching that of Northern Europe.
It is not clear if this increase has resulted from changes in diagnostic procedures in India or if Asian Indians truly have a high prevalence of this disease.
Reenu Malhotra et al. determined the prevalence of IBD in subjects of different ethnic origins who underwent colonoscopy from January 2008 through December 2013 throughout the US. Their mucosal biopsies were evaluated by a single group of histopathologists. Data were compared among subjects categorized as Indian (persons with ancestry in the Indian subcontinent), East Asian (China, Korea, Japan, and Vietnam), Hispanic, Jewish, and other (whites and African Americans not specifically identified with any of the other groups).
Of the 1,005,915 patients included in the study (median age, 60 years; 51% female), 30,812 were diagnosed with IBD (20,308 with ulcerative colitis, 7706 with Crohn’s disease, and 2798 with indeterminate colitis).
Ulcerative colitis was more commonly associated with Indian and Jewish ethnicity and less commonly associated with East Asian and Hispanic ethnicity.
A similar pattern was observed for Crohn’s disease and for IBD overall (see figure).
Among Indian patients, 11.7% of those of Gujarati origins had IBD, compared with 7.9% of other Indians (odds ratio, 1.5). However, the proportion of severe disease was the same among all Indians (14.2%).
The findings are not entirely new—the authors say that an epidemiology study that collected data from 1972 to 1989 found that South Asians and people of South Asian ancestry living in Leicestershire, England had twice the risk for ulcerative colitis compared with Europeans living in the same area. The study concluded that Hindus and Sikhs had “one of the highest [standardized incidence of true ulcerative colitis] in any population or region in the world.”
It is not clear why the prevalence of IBD is lower in India than for Indians in the US. Malhotra et al. propose that genetic factors may interact with new environmental conditions to promote development of IBD.
The authors state that one shortcoming of the study was their lack of information about the patients’ birthplace. They say that based on migration history in the US, it is likely that most patients of Indian, Chinese, and Korean ancestry younger than the age of 20 were born in the US, whereas older individuals are first- and second-generation migrants.
Malhotra et al. say that the findings have relevance to the practice of gastroenterology in Western countries such as the UK, continental Western Europe, and the US, where there are sizable portions of the population with roots in the Indian subcontinent.