Association between ambient temperature and mortality risk and burden: time series study in 272 main Chinese cities

Objectives

To examine the association between temperature and cause specific mortality, and to quantify the corresponding disease burden attributable to non-optimum ambient temperatures.

Introduction

In the context of global climate change, accumulating epidemiological evidence indicates that abnormal ambient temperatures could increase the risk of death from a wide range of cardiorespiratory diseases.123 Knowledge of the optimum temperatures that correspond to minimum mortality (termed as the minimum mortality temperature), as well as the relative risks of mortality from various cardiorespiratory diseases due to non-optimum temperatures, are important to investigate the underlying pathophysiological pathways and to project disease burden associated with climate change.4

Previous studies have focused on either estimating the relative risks for extreme weather events or characterising the associations between exposure and response.5 Consequently, less is known about the relative contribution of moderate and extreme non-optimum temperatures to the whole disease burden using measures such as attributable fractions and attributable numbers.678 Such evidence is important for planning suitable risk communication to the public, tailoring the programmes for public health interventions and evaluating the overall disease burden due to non-optimum ambient temperature.6 Furthermore, previous single city or regional studies have adopted various analytical approaches and different model specifications (particularly lag periods), reducing the comparability of results across climates and populations.123 In a multicentre study, researchers evaluated the exposure-response associations between temperature and total mortality and estimated the total mortality risk attributable to moderate and extreme non-optimum temperatures.69 However, little knowledge was available about the optimum temperatures and the relative risks of mortality from cardiorespiratory diseases associated with non-optimum temperatures, as well as the relative contributions of moderate and extreme non-optimum temperatures on cause specific mortality. Also, researchers used various study periods in the multicentre study,69which added to the study heterogeneity and limited the comparisons of mortality risk and burden in diverse climatic zones.

Therefore, with an established nationwide dataset including 272 main Chinese cities, the present study aimed to examine the associations between temperature as a whole and cause specific mortality, and to quantify the corresponding disease burden attributable to moderate and extreme non-optimum temperatures. We then examined various potential effect modifiers, including demographic, climatic, geographical, and socioeconomic characteristics.