Moderately cold temperature associates with high cardiovascular disease mortality in China

Abstract

Ambient air temperature is a key index that affects human health, including mortality risks of cardiovascular disease (CVD). This study quantitatively investigated CVD mortality burden with respect to various segments across the climatic temperature range. Daily data on average temperature and CVD deaths in nine Chinese cities during 2010–2016 were collected for the study. The association between temperature and city-specific CVD mortality was investigated with a distributed lag nonlinear model across lag 0–21 days for cold temperature and lag 0–2 days for hot temperature, and then pooled the association results in a multivariate meta-analysis to derive the pooled estimates of temperature on CVD mortality at national level. Attributable fractions of CVD mortality to cold- and heat-related (i.e., at temperatures below and above the minimum mortality temperature [MMT]) were calculated. In addition, temperature was further separated at 1 °C intervals of ambient temperature and the attributable fractions of each range were calculated. The results showed that the MMT varied from the 71th to 79th percentiles of temperature in nine Chinese cities, centering at 76th at national level. In total, 16.88% of CVD mortality was attributable to nonoptimal temperature, ranging from 9.73% in Hefei to 24.48% in Nanjing. Cold temperature was responsible for most CVD death burden, with a fraction of 14.62%, compared with 2.26% CVD mortality for heat at overall level. The results of temperature stratification suggested that the highest CVD deaths due to temperature fall within moderate cold. Specifically, the highest attributable fractions were at 7 °C, 7 °C, 8 °C, 4 °C, 5 °C, 4 °C, 4 °C, 5 °C, and 6 °C for Harbin, Changchun, Shenyang, Beijing, Shijiazhuang, Nanjing, Hefei, Shanghai, and Chengdu, respectively. Furthermore, the highest CVD deaths due to temperature were near at the start and end time of heating for five northern cities (Harbin, Changchun, Shenyang, Beijing, and Shijiazhuang). Hence, moderately cold temperature plays a noticeable role in impact mortality. Although moderate cold had a slightly lower relative risk than extreme cold, it occurred on more days than did extreme cold. Finally, the cumulative total counts of CVD deaths caused by moderate cold were the largest. We should pay more attention to the adverse health effects of moderate cold in the future. Additionally, the government and heating departments should slow down the rate of increase (or decrease) temperature at the start (or end) time of heating during moderate time in northern China. The findings have important implications for health promotion and disease prevention strategies of adverse temperatures.