Mortality, morbidity and healthcare costs of short-term high temperatures and heatwaves exposure in older populations: a global systematic review and meta-analysis

Background

Exposure to heat extremes is associated with higher rates of mortality, morbidity and healthcare costs. In the context of population ageing and climate change, which is expected to make extreme heat events more intense, frequent, prolonged, and widespread, understanding their health impacts on older adults is crucial for informing targeted interventions.

Methods

This systematic review and meta-analysis searched PubMed, Embase, Web of Science, Scopus, CINAHL, and AgeLine for studies published between January 1, 1990, and March 15, 2025. Original research articles assessing morbidity, mortality, and healthcare costs among older adults during periods of high temperatures or heatwaves were included. Eligible studies used observational designs, such as time series, case-crossover, or case time-series, comparing risks across different exposures or time periods. Reviews, commentaries, grey literature, animal studies, and studies not focused on temperature as the primary exposure were excluded. Risk estimates were extracted from published studies. A random-effects meta-analysis was conducted to pool relative risks of morbidity and mortality, focusing on specific disease categories according to ICD-10 codes, climate zones, and demographic factors. The certainty and strength of the evidence were assessed following the Navigation Guide systematic review methodology framework. The study protocol was registered with PROSPERO (CRD42023423311).

Results

Out of 21,610 identified studies, 623 were eligible, spanning six continents and 305 locations classified by Köppen climate zones. Of these, 578 were included in the meta-analysis, 43 in a supplementary meta-analysis, and four on healthcare costs were narratively synthesised. A 1°C temperature rise was associated with higher morbidity (RR 1.016 [CI95% 1.012–1.019]) and mortality (RR 1.022 [CI95% 1.020–1.024]) among older people. The highest morbidity risks were linked to heat-related illnesses, external causes and endocrine diseases, and in tropical climates. Mortality risk was highest for intentional self-harm and external causes, chronic obstructive pulmonary disease (COPD), and in Mediterranean climates, with the strongest overall impact on those aged ≥ 85 years. Heatwaves increased morbidity (RR 1.189 [CI95% 1.146–1.233]), particularly for heat-related illnesses and external causes, with the highest overall risk seen in adults aged 75–84 and in subtropical climates. Mortality also rose (RR 1.117 [CI95% 1.105–1.129]), especially for cerebrovascular, endocrine and respiratory diseases, with the greatest overall risks found in tropical climates and among individuals aged ≥ 85 years. Despite the limited number of studies on healthcare costs they showed significant increases in costs during heat exposure for emergency department presentations, respiratory and ureter calculus hospitalisations. There was high heterogeneity with morbidity (high temperatures: I2 = 84.1%; heatwaves: I2 = 97.6%), whilst for mortality, there was no observed heterogeneity with high temperatures (I2 = 0.0%) and moderate heterogeneity with heatwaves (I2 = 72.2%). The strength of evidence was rated as “sufficient” for an association between heat exposure and increased mortality and morbidity in older adults, and “limited” for healthcare costs.

Conclusion

This review highlights the critical impact of heat exposure on the health of older adults, particularly in different climate zones, and indicates a potential increase in healthcare costs associated with this risk. With the global rise in temperatures and ageing populations, heat-related health risks will continue to increase. Effective, evidence-based interventions, such as tailored heat health action plans that consider individual risk factors, local resources, climatic characteristics and healthcare infrastructure, are crucial to minimise these risks.