Secular acceleration of growth in height in Japanese and its social background.

To clarify the true amount of the secular trend of growth in height in Japanese children, birth-year cohorts affected by World War II were excluded from an analysis of the trend in age of maximum increment in mean height (MI age) during the last 80 years. The cohort which experienced the war had an abnormally high maximum annual increment, asymmetry of the histogram representing the annual increments and a poor fit of the logistic function to the adolescent growth curve. The cohorts in which growth in height was under the influence of the great social changes of the war were statistically discriminated according to these three abnormalities of the growth pattern. Since the cohorts which underwent MI age just after the war showed a distorted growth, it is evident that the post-war rapid lowering of MI age for cohorts from 1934 to 1946 should be taken as a convalescent stage after the war-time repression of growth. Excluding the period affected by the war, MI age of both sexes has become earlier by some 0.2 years per decade. The variety of possible causes of the trend towards earlier maturity was investigated by making use of the post-war rapid decline of MI age. Better nutrition is not believed to be the main factor in the trend of growth. Urban population ratio and Engel's coefficient closely paralleled the decline of MI age, which indicates that the progression of urbanization as a way of life has been of prime importance.