Temperature, temperature extremes, and cause-specific respiratory mortality in China: a multi-city time series analysis

Chronic respiratory diseases cause huge death burden worldwide, especially in developing countries. The influence of ambient temperature on respiratory mortality has attracted growing concerns in the background of climate change. Daily cause-specific respiratory deaths and meteorological variables were collected from 16 Chinese cities during 2007-2013. We first applied the distributed lag non-linear model for each city to calculate the percentage change in respiratory mortality risk with a 1 degrees C change in moderate and extreme temperature range. Then, random-effect meta-analytical approach was used to produce the pooled effects. Individual-level and city-level effect modifications were separately assessed by the stratified analysis and mixed effects meta-regression model. Both cold and heat effects were associated with respiratory mortality. The pooled excess risk was 4.40% (95%CI: 2.75-6.08%), 2.23% (1.19-3.28%), 2.64% (1.81-3.47%), and 4.21% (3.10-5.33%) for 1 degrees C change among extreme cold, moderate cold, moderate heat, and extreme heat, respectively. Positive heat and cold effects were found for COPD, asthma, and pneumonia, among which asthma was most vulnerable to extreme cold temperatures, with the effect estimate of 6.52% (2.73-10.46%). The heat effects were much higher in females than males. Slightly higher risks were also observed in the elderly during the heat, and those with lower education level during the heat and extreme cold. City-level modifiers included green coverage rates and diurnal temperature range. Ambient heat and cold temperatures are positively associated with respiratory mortality in China. Individual and city-specific effect modifiers should be taken into consideration in policy-making.