Objective To assess the associations between ambient temperatures and hospitalisations for coronary heart disease (CHD) and stroke.
Methods Our study comprised all residents living in Ontario, Canada, 1996–2013. For each of 14 health regions, we fitted a distributed lag non-linear model to estimate the cold and heat effects on hospitalisations from CHD, acute myocardial infarction (AMI), stroke and ischaemic stroke, respectively. These effects were pooled using a multivariate meta-analysis. We computed attributable hospitalisations for cold and heat, defined as temperatures above and below the optimum temperature (corresponding to the temperature of minimum morbidity) and for moderate and extreme temperatures, defined using cut-offs at the 2.5th and 97.5th temperature percentiles.
Results Between 1996 and 2013, we identified 1.4 million hospitalisations from CHD and 355 837 from stroke across Ontario. On cold days with temperature corresponding to the 1st percentile of temperature distribution, we found a 9% increase in daily hospitalisations for CHD (95% CI 1% to 16%), 29% increase for AMI (95% CI 15% to 45%) and 11% increase for stroke (95% CI 1% to 22%) relative to days with an optimal temperature. High temperatures (the 99th percentile) also increased CHD hospitalisations by 6% (95% CI 1% to 11%) relative to the optimal temperature. These estimates translate into 2.49% of CHD hospitalisations attributable to cold and 1.20% from heat. Additionally, 1.71% of stroke hospitalisations were attributable to cold. Importantly, moderate temperatures, rather than extreme temperatures, yielded the most of the cardiovascular burdens from temperatures.
Conclusions Ambient temperatures, especially in moderate ranges, may be an important risk factor for cardiovascular-related hospitalisations.
- heart disease
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Contributors HC, EL, AG, RTB, MSG, SC, LB, AY and RC contributed to study design issues; HC, QL and JW prepared and cleaned the data; QL, JW, HC, LB, EL, AG, RTB, MSG and SC contributed to the data analyses; LB and HC drafted the manuscript; all authors contributed to interpretation of data, provided critical revisions to the manuscript and approved the final draft.
Funding This study was supported by a contract from Health Canada (contract number: 4500302837). This study was also supported by the Institute for Clinical Evaluative Sciences (ICES), which is funded by an annual grant from the Ontario Ministry of Health and Long-Term Care (MOHLTC). Dr Gasparrini was supported by a grant by Medical Research Council UK (Grant ID: MR/M022625/1) Parts of this material are based on data and information compiled and provided by Canadian Information Health Institute (CIHI). The opinions, results and conclusions reported in this article do not necessarily represent the views of ICES, MOHLTC or CIHI.
Competing interests None declared.
Ethics approval The Research Ethics Board of the University of Toronto (protocol reference 28527).
Provenance and peer review Not commissioned; externally peer reviewed.
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