Background: There is increasing evidence that both temperature extremes and variability are risk factors for mortality. However, it is still unknown whether temperature variability is a modifier of the temperature-mortality relationship. Methods: We collected daily mortality and mean temperature from 511 communities in 28 countries/regions across the world. Temperature variability was calculated by the standard deviation of daily mean temperature at lags of 0-3 days. Community-specific time series model was used to examine the linear effect of heat (lag 0-3 days) on mortality in summer, while controlled for impacts of temperature variability and modelled their interaction on mortality. Random-effect meta-analysis was applied to summarise the city-specific associations. Results: The preliminary results of this study show that the effects of temperature on mortality were slightly higher when not controlling for temperature variability. For the interaction analysis, the lower the temperature variability, the higher the heat effects on mortality. However, the interaction effect was not statistically significant. At international level, each 5 celsius degree increase of temperature was associated with 2.8% (95% CI: 2.3%, 3.3%) increase of mortality in the first quartile of temperature variability, while there was 2.3% (95% CI: 1.8%, 2.8%) increase of mortality in the fourth quartile of temperature variability. The trends were similar for all cities/countries/regions, although there was significant variation in the heat impacts. Conclusion: The findings suggest no apparent need to control for temperature variability when modelling the heat effects on mortality. On behalf of the MCC Collaborative Research Network.
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