Ambient temperature and risk of cardiovascular morbidity and mortality: a nationwide study of vulnerability factors

Abstract Background Ambient temperature is a major environmental determinant of cardiovascular health. However, evidence on the association between temperature and cause-specific cardiovascular health outcomes is still limited. Moreover, little is known about the differential effects across population groups and the contextual factors that exacerbate or reduce vulnerability. A comprehensive assessment is therefore needed to fill this literature gap, and thus inform health adaptation policies to best tackle the negative health consequences of climate change in a context of accelerated rising temperatures and population ageing. Purpose We assessed the effect of temperature and temperature variability onto cause-specific mortality and emergency hospitalisations from cardiovascular causes of diseases in Spain, as well as the effect modification of this association by individual and contextual factors. Methods We collected data on health (hospital admissions and mortality), weather (temperature and relative humidity) and relevant contextual indicators for 48 Spanish provinces during 2004-2019. The statistical analysis was separately performed for the summer (June-September) and winter (December-March) months. We first applied a generalised linear regression model with quasi-Poisson distribution to estimate daily, short-term, province-specific temperature-lag-health associations, and then fitted multilevel multivariate meta-regression models to evaluate the effect modification of contextual factors on heat- and cold-related risks. Results Heat did not contribute to the risk of hospitalisation from cardiovascular diseases, but it considerably increased the risk of mortality, with the strongest effect for hypertension (relative risk [RR] at 99th temperature percentile: 1·510 [95% eCI 1·251 to 1·821]) and heart failure (1·528 [1·353 to 1·725]). We found significant risks related to cold for all cardiovascular causes, with heart failure (RR at 1st temperature percentile: 1·537 [1·329 to 1·779]) exhibiting the greatest risk for hospitalisation, and acute myocardial infarction (1·860 [1·546 to 2·238]) for mortality. Women and the elderly were more vulnerable to heat, while people with secondary education were less susceptible to cold compared to those not achieving this educational stage. Results from meta-regression showed that increasing heating access to the highest current provincial value (i.e. 95.6%) could reduce deaths due to cold by 59·5% (57·2 to 63·5). Conclusions Exposure to heat and cold was associated with a greater risk of morbidity and mortality from multiple cardiovascular conditions, and heating was the most effective societal adaptive measure to reduce cold-related mortality.