Cohort Phenomenon shown in the Transition of the Death from Nephritis and Nephrosis in Japan

The death rate for Nephritis and Nephrosis today is not as remarkable as it was about fifty years ago, but these are still very serious complications in diseases of the circulatory system and in Diabetes Mellitus. We did research on the transition of deaths from Nephritis and Nephrosis from 1900 to 1976 in Japan, using cohort-analysis to get factors related to deaths from those diseases. Our findings are as follows: 1) The death rate for Nephritis and Nephrosis increased rapidly from a level of 30.0 per 100, 000 population in 1900, to a peak of 107.7 in 1923, then it decreased rapidly to a level of 6.1 in 1976. 2) Death rates in the age class of 0-4 years old for cohorts born between 1916 and 1920 were 113.3 for males and 99.9 for females. Those for cohorts born between 1961 and 1965 were 1.4 for males and 1.0 for females. The age-specific death rate curves for each five years were not tracable as rectilinear lines on semi-logarithmic papers, except for the last period for females. Aging, itself, showed little relationship to deaths from these diseases. 3) Cohort analyses of death rates for Nephritis and Nephrosis showed Cohort-Phenomena for both sexes. The death rates of the cohorts, born between 1926 and 1930, or before, increased with age until 1940. Older cohorts, born between 1906 and 1910 or before, had almost fixed death rates for the diseases after 1940. 4) An comparison of the transition of the death rates for the diseases by prefectures showed time-differences in their peaks. Peaks occurred first in urbanized prefectures such as Tokyo, Osaka, and Kyoto, then in neighboring areas, and last in rural areas.