Birth-cohort phenomenon in the time trends of mortality from ulcerative colitis.

It has been suggested that the mortality trends of ulcerative colitis in England and Wales are shaped by an underlying birth-cohort phenomenon. This pattern implies that exposure to an environmental risk factor early in life plays a crucial role in the development of the disease. The authors tested whether the birth-cohort pattern is unique to British mortality statistics or a common feature of ulcerative colitis in western countries by using the vital statistics from England and Wales, Canada, Scotland, Switzerland, The Netherlands, and the United States. Ulcerative colitis death rates from the six countries were plotted against the periods of death or periods of birth. Mortality from ulcerative colitis increased in successive generations born throughout the second half of the 19th century. It peaked in subjects born between 1880 and 1890 and has declined since then. Strikingly similar patterns were found in the six countries and when women and men were analyzed separately. The birth-cohort pattern indicates that development of ulcerative colitis is strongly influenced by one or several environmental risk factors, which act during a short period early in life. In western countries, exposure to this risk has changed in a similar fashion.