 Together, ulcerative colitis and Crohn's disease affect about a million people in the United States.As with Crohn's disease, the rates of UC are greater among Ashkenazi Jews and decreases progressively in other persons of Jewish descent, non-Jewish Caucasians, Africans, Hispanics, and Asians.Appendectomy prior to age 20 for appendicitis and current tobacco use are protective against development of UC.