Shift of the short-term temperature mortality relationship by a climate factor - some evidence necessary to take account of in estimating the health effect of global warming

Several studies have reported a 'V'-shaped relationship between short-term temperature and mortality rates, characterized by mortality rates that are higher when the temperature is extremely low or high than when the temperature is moderate. To quantify the effect of adaptation to a certain climate on this V-shaped short-term temperature-mortality relationship, we studied the prefecture-specific relationship between daily maximum temperature and mortality rates for 65+-years-old Japanese from 1972 to 1990. For both genders, the optimum daily maximum temperature (OT) category at which the mortality rate was minimum ranged from 23C-28 C to 33+C, and the OT level became lower when the climate became colder. The mean OT level was lower for women than for men by 1.7C. The mortality rate at the OT was almost constant across prefectures, regardless of the climate. From the results, we considered that the adaptation effect on the short-term temperature-mortality relationship is mainly described by the 'horizontal shift model': the V-shape moves horizontally according to the climate. This 'shift' should be taken into account in estimating the health effect of global warming, and the model would be useful for the estimation.