Ambient temperature and mortality: An international study in four capital cities of East Asia

Extreme ambient temperature has been associated with increased daily mortality across the world. We describe the ambient temperature–mortality association for four capital cities in East Asia, Seoul, Beijing, Tokyo, and Taipei, and identify a threshold temperature for each city and the percent increase in mortality. We adapted generalized linear modeling with natural cubic splines (GLM + NS) to examine the association between daily mean apparent temperature (AT) and total mortality, as well as mortality due to respiratory (RD) and cardiovascular (CVD) causes in a threshold model. We conducted a time-series analysis adjusting for day of the week and long-term time trend. The study period differed by city. The threshold temperature for all seasons was estimated to be 30.1–33.5 °C, 31.3–32.3 °C, 29.4–30.8 °C, and 25.2°–31.5 °C for Seoul, Beijing, Tokyo, and Taipei, respectively, on the same day. For the mean daily AT increase of 1 °C above the thresholds in Seoul, Tokyo, and Taipei, estimated percentage increases in daily total mortality were 2.7 (95% confidence interval (CI) = 2.2–3.1), 1.7 (95% CI = 1.5–2.0), and 4.3 (95% CI = 2.9–5.7), respectively. Beijing provided no total mortality counts. Estimated percentage increases were 2.7–10.5 for RD mortality, 1.1–9.3 for CVD mortality in 4 cities. This study identified increased mortality due to exposure to elevated AT. The importance of effects of AT and city-specific threshold temperatures suggests that analyses of the impact of climate change should take regional differences into consideration.