Heat disorder in Yamanashi Prefecture during the summer from 1995 to 2004.

The incidence of heat disorders in July and August during 10 yr (1995-2004) reported for the population of Yamanashi prefecture was analyzed, with special consideration of an aging society, in relation to levels and patterns of phases with high daily maximal temperatures. There was an increasing tendency for years with hot summers in comparison to preceding decades. Two climatic characteristics associated with increased incidence of heat disorders have become apparent: first, sustained phases of atmospheric temperatures exceeding approximately 32 degrees C, second, rapid onset of phases with high maximal temperature after preceding phases of relatively cool weather. The influence of age expressed itself in a peak of heat disorder incidences among older children and adolescents and in an elevated plateau at ages higher than approximately 60 yr. Up to that age, exertional heat disorders prevailed. At higher ages classical, non-exertional heat disorders constituted an increasing fraction. Lethal outcomes among patients suffering from heat disorder was low. Patients older than 70 yr clearly prevailed among the lethal cases. The frequent occurrence of heat disorders among persons of old age puts emphasis on the importance of maintaining social activity to improve well-being in general and physiological resistance against heat in particular, including adequate fluid supply. Because physiological heat defense is limited in an aging population, adequate air conditioning will gain increasing importance in view of the observed tendency for the increasing occurrence of phases with excessively high atmospheric summer temperatures.