The North-South difference of the relationship between cold spells and mortality risk of cardiovascular diseases in China

Abstract

Objective: To analyze the North-South difference of the relationship between cold spells and mortality risk of cardiovascular diseases in China. Methods: The time series analysis method was used to collect the daily counts of cardiovascular mortality data, meteorological data and PM2.5 concentration in the cold season (November to March of the following year) from January 1, 2013 to December 31, 2018 in 280 districts and counties in China. The non-constrained distributed lag linear model was used to analyze the relationship between cold spells and mortality risk of cardiovascular diseases and its North-South difference in China. Results: From 2013 to 2018, the mean of daily average temperature of the cold season in 280 districts and counties was 5.4 ℃. The mean of daily average relative humidity was 64.4%, and the mean of daily average PM2.5 concentration was 73.7 μg/m3. The average cold spell days in each county was 11.7 days per year,the mean of daily average temperature on cold spell days was (-2.4±6.7) ℃, and M (Q1, Q3) was -1.5 (-5.1, 1.1) ℃. The average of daily number of cardiovascular disease deaths in each county/district was (6±5) cases, and M (Q1, Q3) was 5 (2, 8) cases. The percentage change (95%CI) in the South was 4.94% (3.69%, 6.20%) (lag 0 d), higher than that in the North [the percentage change (95%CI) was 1.49% (1.14%-1.84%) (lag 0-7 d)]. In the North, the mortality risk of ≥75 years old was relatively low among three age groups, with a percentage change (95%CI) about 1.63% (1.33%-1.93%) (lag 0-21 d). In the South, the mortality risk of ≥ 75 years old was relatively high among three age groups, with a percentage change (95%CI) about 5.18% (3.78%-6.59%) (lag 0 d). Conclusion: The mortality risk of cardiovascular diseases caused by cold spells in the South is higher than that in the North of China, and the risk peak occurs earlier in the South.