Effect of the thermal environment on mortality: analysis of longitudinal data from Cyprus (2009–2018)

Exposure to a suboptimal outdoor thermal environment is associated with increased morbidity and mortality. This study aimed to examine the effect of the thermal environment on all-cause mortality in Cyprus. Daily mortality data were obtained from 2009 to 2018. Hourly meteorological data were retrieved from the ERA5-Land reanalysis database and air pollutant concentrations were obtained from the official air quality network of the Republic of Cyprus. Air temperature (Tair), the physiologically equivalent temperature (PET), and the universal thermal climate index (UTCI) were used to assess the thermal environment. Associations of Tair, PET, and UTCI with daily mortality were examined using negative binomial regression while adjusting for air quality. Mortality in the cold period (December to March) increased by 3.3% for each 1 °C decrease in Tair and by up to 1.8% for each 1 °C decrease in PET and UTCI (p value < 0.001). In the warm period (April to November), a 1 °C increase in Tair or in PET and UTCI was associated with an increase in mortality of up to 1.4% and 1.1% (p value < 0.001), respectively. The effect (increase in mortality) was more pronounced when the analysis focused on winter (3.6% per 1 °C decrease in Tair, 2.4% per 1 °C decrease in PET, and 2% per 1 °C decrease in UTCI) and summer (4.1% per 1 °C increase in Tair, 2.4% per 1 °C increase in PET, and 1.2% per 1 °C increase in UTCI). Males in cold periods and the elderly (older than 64 years) were more vulnerable. Awareness about the effects of the thermal environment on mortality, including those during the cold months of the year, should be enhanced.