The association between temperature variability and mortality: an international collaborative study

Abstract

Introduction: The evidence is limited for the impacts of temperature variability (TV) within or between days on mortality. In this study, we applied a novel method to calculate TV, and investigated the TV-mortality associations using a large multi-country data set. Methods: We collected daily time series data of temperature and mortality from 372 locations in 12 countries/regions with a wide range of climates (Australia, Brazil, Canada, China, Japan, Moldova, South Korea, Spain, Taiwan, Thailand, UK, and USA). We developed a novel method to calculate TV using the standard deviation of current day’s and preceding days’ minimum and maximum temperatures. Two-stage analyses were used to assess the relation between TV and mortality. Firstly, a Poisson regression model allowing over-dispersion was used to estimate the community-specific TV-mortality relation, after controlling for a long-term trend, seasonality, day of the week, and main effects of daily mean temperature up to 21 days. In the second stage, a meta-analysis was used to pool the effects within each country. Results: There was a significant association between TV and mortality in all countries, even after controlling for the effects of daily mean temperature. In stratified analyses, TV was still significantly associated with mortality in cold, hot, and moderate seasons. Mortality risks related to TV were higher in hot areas than cold areas when using short TV exposure (0–1 days), while TV-related mortality risks were higher in moderate areas than cold and hot areas when using longer TV exposure days (0–7 days). Conclusion: This large multi-country analysis suggests that TV has significant impacts on mortality. Results indicate that more attention should be paid to unstable weather conditions in order to protect health. These findings may have implications for developing public health policies for managing health risks of climate change.