As a result of geographical and chronological studies of the seasonal variation of mortality in Japan, it was concluded that seasonal mortality would decrease along with cultural development of human society, and that the frequency distribution of mortality would gradually turn from a “summer concentration” to a “winter concentration” type (Momiyama, 1963).
Katayama and Momiyama (1972) revealed that the seasonal variation curve has become much flatter in cold regions and deaths remain concentrated in winter in the comparatively warm region. The former seasonal type curve has become so flat that mortality might well be said to have been “deseasonalized” and this can be ascribed to the differences in the system of room heating.
In order to estimate whether the cold climate in Kusatsu is beneficial for human's health, the deviation of the mortality and its relation to its temperature in Kusatsu was studied since 1948, and was compared with those in other hot spring areas in Gunma Prefecture in this paper.
Kusatsu is 1200m above the sea level, and its mean temperature is 3°C lower than that in other hot spring areas, Shima, Ikaho and Minakami (they are 650, 630, 500m a. s. l. respectively).
In Kusatsu, the total mortality was not higher than those in others, and chronologically the seasonal deviation of the mortality would decrease, and the frequency distribution of mortality would gradually turn from a “two-peaks (in winter and in early summer)” type to a “winter concentration” type, and since 1972 the seasonal variation curve has become flatter gradually (Deseasonalization)
Deaths of infants have decreased and those of high-aged increase in death rate year by year. No relation was observed between the frequency distribution of the mortality to those of means of maximal and minimal temperature from normal temperature in each month,
Since 1956 the death rate from stroke has been largest in Kusatsu, but the stroke mortality lower than other areas in Gunma Prefecture, and regression has been observed especially in winter. It was assumed that this can be ascribed to the spread of powerful system of the room heating associated of hot spring bathing, that is available for the in habitants in Kusatsu custumely. But since 1972. deaths from stroke have slightly shown “summer concentration”. Mean temperature in summer is about 20°C in Kusatsu.
In Nakanojo Town, where Shima hot spring area is belonged to, the stroke mortality was higher than that in Kusatsu, and formed winter concentration type.
Deaths from heart diseases have negative coefficience of correlation to temperature both in Kusatsu and Nakanojo.
Infant mortality has no relation to the temperature but the coefficience of correlation to the diurnal ranges of temperature (larger in May, April, March and October) would been slightly positive since 1960.
Many deaths from stroke of hot spring cure guests without medical consultation were occured in 1961-1970 in summer. It was thought that those were due to unsuitable adaptation to the upland's climate and hot spring bathing at high temperature For this reason, the attention may be required to medical control of bathing.
From these results, it was suggested that the cold climate in Kusatsu would have no direct effect on the mortality, and the heating of living room and hot spring bathing have an effect on the low mortality in Kusatsu.