A case-control study of ulcerative colitis in relation to dietary and other factors in Japan. The Epidemiology Group of the Research Committee of Inflammatory Bowel Disease in Japan.

The etiology of ulcerative colitis is essentially unknown. A hospital-based case-control study examined the risk of ulcerative colitis in relation to dietary and other factors. Recruited at 20 hospitals across the nation were 101 ulcerative colitis patients who were 10-39 years old at the time of disease onset and whose disease had been diagnosed within the past 3 years. One hundred and forty-three control subjects were also examined. Information on factors was obtained by using a self-administered questionnaire. Combined consumption of western foods (bread for breakfast, butter, margarine, cheese, meats, and ham/ sausage) was significantly related to an increased risk of ulcerative colitis (trend P = 0.04). Of the six food items of the western food group, margarine was positively and significantly associated with ulcerative colitis (trend P = 0.005), and bread for breakfast tended to be positively associated with the risk (trend P = 0.07). No appreciable association was found for the consumption of Japanese foods, vegetables and fruits, confectionery, or soft drinks. Compared with lifelong nonsmokers, current smokers had a decreased risk, and former smokers had an increased risk. This study confirmed a protective association between smoking and ulcerative colitis, and suggested that margarine or chemically modified fat may play an etiological role in the development of ulcerative colitis.