Introduction: The temperature2mortality relationship follows a well known ‘J V shape’ pattern with mortality excesses at cold and hot temperatures, while the value of minimum mortality temperature (MMT) is used as a proxy of population heat tolerance. As MMT is higher for people living in warmer places, it has been argued that populations will adapt to temperature changes. Objective: To test this notion by taking advantage of a huge migratory flux that occurred in Italy during the 1950s, when large numbers of unemployed from the south moved to the industrialising north-western regions. We analysed, through an ecological study, the mortality2 temperature relationships among residents of Milan (Lombardy) who died between 1980 and 1989, by groups identified by birthplace. We also analysed mortality among Sicilian born residents of Palermo (Sicily). Methods: Log linear models were used to fit daily death count data as a function of different explanatory variables: months, weekdays, holiday, influenza epidemics, temperature, and relative humidity. Results: The pattern of mortality2temperature curves differed by birthplace. Curves for natives of Lombardy showed two breakpoints at 19˚C (MMT) and 26˚C, with no risk for temperatures between two breakpoints: mortality rose sharply over 26˚C. For natives of Sicily, residing either in Milan or in Palermo, only one breakpoint emerged at 23˚C (MMT), and they shared the same curve pattern and the same increase in mortality risks over this value. Conclusions: Results suggest that heat tolerance in populations could be modulated by outdoor temperatures experienced early in life, and complete acclimatisation may not occur if external environmental temperatures increase.
The effect of birthplace on heat tolerance and mortality in Italy 1980’-89
VIGOTTI, MARIA ANGELA;
2004-01-01
Abstract
Introduction: The temperature2mortality relationship follows a well known ‘J V shape’ pattern with mortality excesses at cold and hot temperatures, while the value of minimum mortality temperature (MMT) is used as a proxy of population heat tolerance. As MMT is higher for people living in warmer places, it has been argued that populations will adapt to temperature changes. Objective: To test this notion by taking advantage of a huge migratory flux that occurred in Italy during the 1950s, when large numbers of unemployed from the south moved to the industrialising north-western regions. We analysed, through an ecological study, the mortality2 temperature relationships among residents of Milan (Lombardy) who died between 1980 and 1989, by groups identified by birthplace. We also analysed mortality among Sicilian born residents of Palermo (Sicily). Methods: Log linear models were used to fit daily death count data as a function of different explanatory variables: months, weekdays, holiday, influenza epidemics, temperature, and relative humidity. Results: The pattern of mortality2temperature curves differed by birthplace. Curves for natives of Lombardy showed two breakpoints at 19˚C (MMT) and 26˚C, with no risk for temperatures between two breakpoints: mortality rose sharply over 26˚C. For natives of Sicily, residing either in Milan or in Palermo, only one breakpoint emerged at 23˚C (MMT), and they shared the same curve pattern and the same increase in mortality risks over this value. Conclusions: Results suggest that heat tolerance in populations could be modulated by outdoor temperatures experienced early in life, and complete acclimatisation may not occur if external environmental temperatures increase.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
