Abstract
BackgroundAssociations between air temperature and mortality have been consistently observed in Europe and the United States; however, there is a lack of studies for Asian countries. Our study investigated the association between air temperature and cardio-respiratory mortality in the urban area of Beijing, China.MethodsDeath counts for cardiovascular and respiratory diseases for adult residents (≥15 years), meteorological parameters and concentrations of particulate air pollution were obtained from January 2003 to August 2005. The effects of two-day and 15-day average temperatures were estimated by Poisson regression models, controlling for time trend, relative humidity and other confounders if necessary. Effects were explored for warm (April to September) and cold periods (October to March) separately. The lagged effects of daily temperature were investigated by polynomial distributed lag (PDL) models.ResultsWe observed a J-shaped exposure-response function only for 15-day average temperature and respiratory mortality in the warm period, with 21.3°C as the threshold temperature. All other exposure-response functions could be considered as linear. In the warm period, a 5°C increase of two-day average temperature was associated with a RR of 1.098 (95% confidence interval (95%CI): 1.057-1.140) for cardiovascular and 1.134 (95%CI: 1.050-1.224) for respiratory mortality; a 5°C decrease of 15-day average temperature was associated with a RR of 1.040 (95%CI: 0.990-1.093) for cardiovascular mortality. In the cold period, a 5°C increase of two-day average temperature was associated with a RR of 1.149 (95%CI: 1.078-1.224) for respiratory mortality; a 5°C decrease of 15-day average temperature was associated with a RR of 1.057 (95%CI: 1.022-1.094) for cardiovascular mortality. The effects remained robust after considering particles as additional confounders.ConclusionsBoth increases and decreases in air temperature are associated with an increased risk of cardiovascular mortality. The effects of heat were immediate while the ones of cold became predominant with longer time lags. Increases in air temperature are also associated with an immediate increased risk of respiratory mortality.
Highlights
Associations between air temperature and mortality have been consistently observed in Europe and the United States; there is a lack of studies for Asian countries
We explored the effects of air temperature on mortality within warm period (April to September) and cold period (October to March) separately
After an analysis within the warm period, we found that the order (April to September in 2003 is the 1st warm period, April to September in 2004 is the 2nd one, and April to August in 2005 is the 3rd one.) showed no significant interaction with two-day average temperature, and indicates that there was no heat effect modification by potential population adaption to heat or by possible increasing prevalence of air-conditioning year by year
Summary
Associations between air temperature and mortality have been consistently observed in Europe and the United States; there is a lack of studies for Asian countries. Our study investigated the association between air temperature and cardio-respiratory mortality in the urban area of Beijing, China. Concern on the effects of meteorological factors on population health has increased. The association between air temperature and mortality has been investigated in various locations of the world, either by simple descriptive statistics or by timeseries or case-crossover approaches. Results obtained from heat wave events formed most of the existing evidence of heat effects on mortality from 1970s until today [2]. The 2003 European heat wave and 2006 California heat wave are two prominent recent events. Heat waves and increases in moderate temperature contribute to the observed heat-related mortality. The residents of lower latitudes tended to be more vulnerable only at higher temperature values, indicating less susceptibility to heat [8,9,10]
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