Associations between various types of mortality and temperature variability distinguishing the intraday and interday effects in South Korea

Abstract

Background: The association between temperature variability (TV) and elevated mortality risks is widely known. Yet, few studies investigated the distinct effects of intraday and interday temperature fluctuations considering age-specific, gender-specific, and cause-specific mortality stratified by four seasons.

Objectives: We investigate the associations between total, intraday, and interday temperature variabilities and total, age-specific, gender-specific, cardiovascular, and respiratory mortality year-round and also stratified by four seasons.

Methods: We collected district-level daily data for temperature and total, age-specific, gender-specific, cardiovascular, and respiratory mortality in South Korea from 2011 to 2021 (N = 3,113,425). TV indices (i.e., total TV, intraday TV, and interday TV) were computed as the standard deviations of daily minimum, maximum, and mean temperatures over a lag of one to seven days. The associations between TV and mortality were evaluated by a space-time-stratified case-crossover design with quasi-Poisson regression.

Results: Mortality risks varied based on the type of TV index. The associations also differed depending on the mortality type and the season. Year-round associations showed interday TV was generally associated with elevated mortality risks (total mortality: 0.30% (95% CI: 0.07%, 0.52%), 65+ mortality: 0.32% (95% CI: 0.07%, 0.58%), female mortality: 0.49% (95% CI: 0.16%, 0.82%), CVD mortality: 0.47% (95% CI: 0.02%, 0.92%) on lag0-7) while intraday TV was not significantly associated with increased risk of mortality except for the male mortality, 0.68% (95% CI: 0.04%, 1.32%) on lag0-7. Season-stratified analysis revealed that TV-related mortality risks were high consistently in the spring season and generally in the summer season while the associations were generally negative in fall and insignificant in winter.

Conclusion: This study provided evidence on the season-stratified, independent impacts of intraday and interday temperature variabilities on total, age-specific, gender-specific, and cause-specific mortality risks in South Korea drawing attention to the need of targeted policies to alleviate the impacts on human health.

Keywords: Interday; Intraday; Mortality; Season-stratified; Temperature variability.