Background: Recent investigations have reported a decline in the heat-related mortality risk during the last decades. However, these studies are frequently based on modeling approaches that do not fully characterize the complex temperature–mortality relationship, and are limited to single cities or countries.

Objectives: We assessed the temporal variation in heat–mortality associations in a multi-country data set using flexible modelling techniques.

Methods: We collected data for 272 locations in Australia, Canada, Japan, South Korea, Spain, the United Kingdom, and the United States, with a total 20,203,690 deaths occurring in summer months between 1985 and 2012. The analysis was based on two-stage time-series models. The temporal variation in heat–mortality relationships was estimated in each location with time-varying distributed lag nonlinear models, expressed through an interaction between the transformed temperature variables and time. The estimates were pooled by country through multivariate meta-analysis.

Results: Mortality risk due to heat appeared to decrease over time in several countries, with relative risks associated to high temperatures significantly lower in 2006 compared with 1993 in the United States, Japan, and Spain, and a nonsignificant decrease in Canada. Temporal changes are difficult to assess in Australia and South Korea due to low statistical power, and we found little evidence of variation in the United Kingdom. In the United States, the risk seems to be completely abated in 2006 for summer temperatures below their 99th percentile, but some significant excess persists for higher temperatures in all the countries.

Conclusions: We estimated a statistically significant decrease in the relative risk for heat-related mortality in 2006 compared with 1993 in the majority of countries included in the analysis.

Citation: Gasparrini A, Guo Y, Hashizume M, Kinney PL, Petkova EP, Lavigne E, Zanobetti A, Schwartz JD, Tobias A, Leone M, Tong S, Honda Y, Kim H, Armstrong BG. 2015. Temporal variation in heat–mortality associations: a multicountry study. Environ Health Perspect 123:1200–1207;  http://dx.doi.org/10.1289/ehp.1409070

Address correspondence to A. Gasparrini, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, U.K. Telephone: 0044 (0)20 79272406. E-mail: antonio.gasparrini@lshtm.ac.uk

This study and A.G. were supported by the UK Medical Research Council through a Research Methodology Fellowship (grant G1002296). Y.G. was supported by a University of Queensland Research Fellowship. P.L.K. and E.P.P. were supported by the U.S. National Institute for Environmental Health Sciences (grant ES009089) and by the U.S. National Oceanic and Atmospheric Administration (grant NA10OAR4310212). A.T. was supported by the Ministry of Education of the Spanish Government (Salvador Madariaga’s grant: PRX12/00515). S.T. was supported by a National Health and Medical Research Council research fellowship (no. 553043) and by an ARC Discovery grant (DP110100651). Y.H. was supported by the Environment Research and Technology Development Fund (S-8 and S-10) of the Ministry of the Environment, Japan. M.H., Y.H., and H.K. were supported by the Global Research Laboratory (grant K21004000001-10A0500-00710) through the National Research Foundation of Korea.

The authors declare they have no actual or potential competing financial interests.

Received: 13 August 2014 Accepted: 28 April 2015 Advance Publication: 1 May 2015 Final Publication: 1 November 2015

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