Urban-rural difference in the trend of colo-rectal cancer mortality with special reference to the subsites of colon cancer in Japan.

In order to study the effect of urbanization on the epidemiological features of colo-rectal cancer in Japan, the age-adjusted death rates (AADRs) for right-sided (cecum, ascending and transverse) colon, left-sided (descending and sigmoid) colon and rectum cancers during three periods, 1969-71, 1974-76 and 1979-81, were compared among five areas with different population sizes; ten metropolitan cities (greater than 1,000,000), large cities (1,000,000-150,000), medium-sized cities (150,000-50,000), small cities (less than 50,000) and counties. The AADR for left-sided colon cancer has been increasing in recent years, especially in males, and was higher in urban areas than in rural areas, which may imply that the recent increase in the incidence of left-sided colon cancer is associated with an urbanization of the life styles of Japanese people. In Japan, the daily consumption of carbohydrate has been decreasing, but that of total fat has been increasing in recent years, and the ratio of fat/carbohydrate consumption as an energy source was strongly correlated with the AADRs for left-sided colon cancer among the five areas in the three periods. From this correlation analysis, it was suggested that urbanization of life style, namely, the recent westernization of eating habits of Japanese people might be associated with the recent increase of the AADRs for colon cancer, especially of left-sided colon cancer, in Japan.