Signs Seen in Japan of Deseasonality in Human Mortality

Abstract

With the approach of the 1970's, indications are increasing that the seasonal variation has been getting considerably moderate, i. e. the steady flattening of the winter peak plus the gradual pickup of deaths, simultaneously with the contraction of the death rate. In other words, the seasonal variation itself can be said to be approaching to the extent of deseasonality as already witnessed somehow or other in the North European and North American countries. Such a new trend is seen not only for old people affected mostly by cerebrovascular diseases but also for early infancy under 1 year. Particularly remarkable is the considerable flattening of the variation curve for infant mortality.
A study of death causes for total mortality in the past decades reveals, among others, that communicable diseases account for as much as 46%, contrasted to not more than 13% for senile diseases in the 1930's. The share declines sharply for communicable diseases but rises up for senile ailments to 52% in the 1960's and to 65% in the 1970's, compared with 70% or so in the United Kingdom and United States.
As for cerebrovascular diseases, the seasonal variation is bimodal up to the 1940's, but in the 1950's and 1960's it, changes to the pattern of concentration in winter. Quite recently (1971-73) the winter peak gets tangibly lower, indicative of a visible moderation. A detailed study reveals, however, that the seasonal variation differs widely between cerebral haemorrhage and cerebral thrombosis-embolism, with deaths concentrated in the cold season for the former and with two maxima, a peak in winter and a lower hill in summer, for the latter. Moreover, there is an increasing possibility that the mortality of the latter will curve up on the whole with its summer hill getting more prominent than ever.
Particularly conspicuous is the recent change in the seasonal variation of infant mortality. When the bimodal pattern prevailed in the early decades, death concentration in the cold season wes much more notable for early infancy, but in recent years the winter peak gets lower year after year and stands nearly on the equal level as the summer hillthe gradual return of the bimodal variation pattern with two equally high hills, strikingly contrasted to the 1940-59 bimodal pattern with a prominently high peak in winter.
The return of a summer hill, as seen in infant mortality, claims careful consideration. The winter peak, caused mostly by pneumonia-bronchitis, for instance, has got sharply lower and come to stand as high as the newlyformed summer hill quite recently (1971-73). Such bimodal variation of infant mortality can be regarded as indicating the natural picture of morbidity and mortality inherent in human beings which remain unarrested in spite of all the efforts in every field for better environment and better health.
In order to understand and better visualize the seasonal variation of mortality since the start of the current century and the notable changes recently appearing in the seasonal variation, seasonal variation patterns (models) are drawn decade by decade for important death causes, such as gastroenteritis, tuberculosis, pneumonia-bronchitis and cerebrovascular diseases.
The 1912-73 time series of both the summer and the winter death indices are drawn to see their respective behavior and mutual relationship for tuberculosis, gastroenteritis, cerebrovascular diseases, heart disease and pneumonia-bronchitis.