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Review

What Are the Key Built Environment Features Associated with Heat-Related Health Risks Among Older People in High Income Countries?

by
Susan Strickland
and
Michael Tong
*
National Centre for Epidemiology and Population Health, ANU College of Health and Medicine, The Australian National University, Canberra, ACT 2601, Australia
*
Author to whom correspondence should be addressed.
Green Health 2025, 1(1), 2; https://doi.org/10.3390/greenhealth1010002
Submission received: 19 March 2025 / Revised: 18 April 2025 / Accepted: 28 April 2025 / Published: 30 April 2025
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Abstract

:
The study aims to identify key features in the built environment that are associated with heat-related health risks among older people in high-income countries, which could inform the development of targeted interventions to reduce built-environment-related heat risks for older populations in the context of climate change. We conducted a systematic review to identify features of the built environment associated with the health impacts of heat amongst people aged 65 or over, living in urban areas. Three databases, PubMed, Scopus, and Web of Science, were searched for the period from database inception until February 2025. The key built environment features associated with adverse health outcomes among older people included urban land surface vegetation, impervious ground surfaces, orientation of bedrooms, top floor locations of apartments, housing age, and the presence and use of air conditioning. The health indicators used in this study were heat-related mortality and morbidity represented by hospitalisations and ambulance call-outs. Built environment features were significantly associated with heat-related health risks among older people. Given the increasing high temperatures and more frequent and intense heatwaves in the context of climate change, there is an urgent need to develop targeted built environment adaptation plans for older people to strengthen their resilience to heat and reduce heat-related adverse health impacts.

1. Introduction

Climate change, increasing urbanisation, and ageing represent major global challenges to population health. The Intergovernmental Panel on Climate Change has predicted that future heatwaves in urban areas will occur more frequently, with greater intensity, and for longer durations [1]. The proportion of people aged over 65 is predicted to grow from 10% of the global population in 2021 to 17% in 2050 (from 761 million in 2021 to 1.6 billion in 2050) [2]. Further, the proportion of older people is projected to be greater in high-income countries compared with low- and middle- income countries. Globally, by 2050, a 65-year-old person is expected to live an additional 19.8 years on average [3]. Moreover, these high-income countries have significantly greater proportions of older people living independently in the community (75% in high-income countries, declining along a gradient to 15% in low-income countries) [4].
The built environment has been described as the human-made surroundings where people live, work, and recreate, which includes physical buildings and parks, and supporting infrastructure [5]. Its role as a contributor to health outcomes is likely to become more important due to increasingly high temperatures in the context of climate change and the effects of the urban heat island (UHI) [6], particularly given the greater susceptibility of an ageing population to heat [7,8,9]. The increasing frequency of high-temperature days and heatwave events can have both direct health impacts (e.g., dehydration, heat stress, heat stroke) and indirect health impacts (e.g., reduced ongoing health benefits of outdoor exercise). This is of significant concern for older adults due to their reduced thermoregulatory ability to maintain core body temperature around 37 °C [10]. These adverse health effects are often exacerbated by chronic health conditions such as hypertension, cardiovascular disease, diabetes, and reduced mobility or cognitive function [11].
Studies of the built environment and health have demonstrated positive and negative impacts on older adults’ health [12,13]. Built environment features, including more green spaces, better housing conditions, and installation of air conditioning, have been associated with a positive impact on older adults’ health during the hot days [13,14,15]. In contrast, other built environment features, such as poor building orientation, inappropriate construction methods or materials, inadequate insulation, poor ventilation and cooling systems, and lack of effective tree cover or other forms of shading, can exacerbate overheating and increase heat-related health risks [6,16]. Moreover, living on the upper floors of high-rise buildings can also result in further exposure to increased heat from poorly insulated roofing and higher solar gain [16,17]. These risks are particularly pronounced in high-density urban environments, where the urban heat island effect can significantly intensify indoor temperatures [18].
In 2018, 55% of the global population lived in urban areas; this proportion will increase to 68% by the middle of this century [19]. In high-income, highly urbanised countries such as Australia, the percentage of urban population is expected to be even higher, and reach 69–70% by 2027 [20]. In 2020, 66% of the Australian population aged over 65 lived in the major cities [21]. This demographic distribution poses a significant challenge in accommodating and adapting to the needs of older populations in the urban built environment in high-income countries. The older adults are more vulnerable to extreme heat compared to younger adults, due to reduced sensitivity to increased temperatures and decreased thermoregulation capacity. However, these risks have not been appropriately mitigated through actions aimed at reducing the heat exposure [22,23]. Although growing attention has been directed toward these issues through initiatives such as the United Nations Decade of Healthy Ageing and the World Health Organisation Global Network for Age-friendly Cities and Communities, it is still regarded as being a relatively neglected area of climate-change research [24,25]. Moreover, high-income countries significantly differ from low- and middle-income countries in terms of socioeconomic status, energy consumption, and built environment characteristics [26,27]. Given these contextual differences, this review focuses exclusively on studies conducted in high-income countries to explore the built environment features associated with heat-related health outcomes among older adults. These settings also serve as exemplars for future scenarios in which a growing proportion of ageing populations live independently within increasingly urbanised environments.
The aim of this systematic review is to address the critical research gap by identifying key features in the built environment that exacerbate or ameliorate the health impacts of high temperatures and heatwaves for older people living in urban areas in high-income countries. The findings from this review could inform the development of targeted interventions to reduce heat-related health risks associated with built environment features and mitigate the adverse health impacts among this vulnerable older population in the context of climate change.

2. Methods

2.1. Search Strategy

A systematic search of peer-reviewed literature was conducted to identify features of the built environment associated with the health risks of high temperature and heat amongst older people. For the purpose of this review, built environment features are the elements that constitute the surroundings where older people live their daily lives (particularly housing, public and community buildings such as libraries, clubs, shops, parks, and streetscapes). The review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines on conducting and reporting [28]. Three databases, PubMed, Scopus, and Web of Science, were searched for this review. The search covered peer-reviewed literature published from database inception until February 2025, using keywords including built environment, health risk, high temperature, heat, and older people. Detailed search terms can be found in the Supplementary Materials. The protocol for this review was registered with PROSPERO (International Prospective Register of Systematic Reviews registration, CRD 42023407562).

2.2. Inclusion and Exclusion Criteria

This systematic review was limited to peer-reviewed studies published in English with a focus on built environment features associated with the health impacts of high temperatures and heatwaves amongst people aged 65 or over. To ensure internal consistency of characteristics among the older population, the review was limited to populations aged 65 years or over, with and without pre-existing health conditions, residing independently within urban communities in an Organisation for Economic Co-operation and Development (OECD) Category 1 country (high-income countries) [29]. High-income countries had greater proportions of older people and greater longevity. They also still have significantly greater proportions of older people living independently in the community compared to all other economic groupings of countries [4]. Studies examining built environment features only, without considering heat-related health impacts, and studies on older people living in residential care or purpose-built retirement accommodation, were excluded from this review. Editorials, reviews, letters, commentaries, conference abstracts, posters, books, and grey literature were also excluded. Full inclusion and exclusion criteria can be found in the Supplementary Materials.

2.3. Evidence Selection and Data Extraction

To identify relevant studies, a two-step procedure using Covidence [30] was applied. First, titles and abstracts were screened against inclusion criteria by the independent reviewers and shortlisted. Second, the selected articles were obtained for full-text review and assessed in detail against the inclusion criteria. Any disagreements or inconsistencies in the screening were resolved via discussion among the reviewers.
A Covidence data extraction spreadsheet was customised for this review (Table S1), and information from the included studies was extracted into the customised spreadsheet, including first author, year of publication, title, study site, study population, study period, study design, built environment features, health indicators, and key findings. Data extraction was undertaken by one reviewer and checked by the other reviewer, with any disagreements resolved through group discussion among the reviewers.

2.4. Assessment of Quality of Evidence

The quality of included studies was assessed using a modified version of the National Institutes of Health (NIH) Quality Assessment Tool for Observational Cohort and Cross-sectional Studies [31]. The tool evaluates the validity of a study including research question, study population, sample size, exposures, outcomes, adequacy of timeframe and exposure measurements, confounding factors, and whether outcomes were consistently measured and reported to ensure data quality.

3. Results

3.1. Search Results

The systematic database search generated 5057 records, which were imported into Covidence for screening and data extraction, with 431 duplicates removed. After initial title and abstract screening, 186 articles were identified for full-text review. Of these, 29 articles met the inclusion criteria. An additional three articles were identified from manual backward citation searching of the included studies. Finally, a total of 32 articles were included in this systematic review (Figure 1).
Table 1. Summary of key characteristics of included studies.
Table 1. Summary of key characteristics of included studies.
Author, Year of PublicationStudy Site/s
(Climate Zone)		Study DesignStudy PeriodBuilt Environment Features
(Methods for Ascertaining)		Heat-Related Health Impacts
Alberini et al., 2011 [32]Canada: Winnipeg, Windsor, Fredericton, Regina and Sarnia
(Humid continental climate)		Observational—Cross-sectional2–18 September 2010Central or window air conditioning (AC)
(Survey, objective measurement)		Morbidity and
self-perceived health including dizziness, nausea, difficulty breathing, dehydration, mild and severe heat exhaustion, heat stroke, and other cardio- or cerebrovascular symptoms.
Bélanger et al., 2016 [33]Canada: Quebec
(Arctic, Subarctic, and Humid continental climate)		Observational—Cross-sectional2010–2011AC; thermal insulation of dwelling; walkability; green spaces
(Survey, objective measurement)		Morbidity—Self-reporting of adverse physical health during very hot and very humid summer conditions.
Crank et al., 2024 [34]USA: Houston, Phoenix, Los Angeles
(Humid subtropical, Hot desert, and Mediterranean climate)		Observational—Cross-sectional2017AC; white roof; weatherisation
(Survey, objective measurement)		Morbidity—Heat-related health symptoms.
Eisenman et al., 2016 [35]USA: Maricopa County, including Phoenix, Arizona
(Desert climate)		Observational—analytical2005–2010Walkable access (≤ 0.89 km) to publicly accessible cooled spaces; home AC; thermal protective properties of residential buildings and features contributing to thermal characteristics—wall materials (concrete block, wood frame), insulation thickness, windowpanes, attic insulation, roofing material, and size of home.
(Census tract, objective measurement)		Mortality—All-cause and heat-related illness.
Fujimoto et al., 2023 [36]Japan
(Humid subtropical, Humid continental, Tropical rainforest climate)		Observational—Cross-sectional2018–2019AC
(Survey, objective measurement)		Morbidity—Heatstroke
Gronlund et al., 2015 [37]USA: Michigan
(Humid continental climate)		Time-stratified case-crossoverMay–September, 1990–2007Percent of homes built before 1940, 1940–1959, 1960–1979, and after 1979; green space.
(Census tract, objective measurement)		Mortality—Primary causes of death coded as all-cause, heat-related, cardiovascular, and respiratory mortality.
Gronlund et al., 2016 [38]USA
(Semi-arid, Desert, Humid continental, Humid temperate, Humid subtropical, Mediterranean, Tropical, Oceanic, Subarctic, and Polar climate)		Observational—case-crossoverMay–September, 1992–2006Pre-1940 housing; Land cover classifications and percent of area non-greenspace (not classified as open water, developed open space [mostly lawn grasses], forest, shrubland, scrub, agricultural, grasses or wetlands).
(Census tract, objective measurement)		Morbidity—Hospitalisation for respiratory and renal/heat; including any contributing causes coded as heat-related illness.
Guirguis et al., 2018 [39]USA: San Diego
(Mediterranean climate)		Observational—AnalyticalMay–October 1999–2013AC
(Survey, objective measurement)		Morbidity—Hospitalisation. Unscheduled at acute care facilities for all cardiovascular diseases (CVD) and respiratory diseases, acute renal failure, mental health, dehydration, and heat illness.
Hansen et al., 2022 [40]Australia: Adelaide and suburbs, Iron Triangle; and Fleurieu Peninsula
(Mediterranean climate)		Mixed methods—observational and simulationMay 2018; January to October 2019House and roof materials; insulation; presence/usage of AC
(Survey, objective measurement)		Morbidity—Self-Perceived Health: Coronary disease, fatigue or tiredness, shortness of breath, sleeplessness, and dizziness.
Diseases or symptoms found to affect thermal sensation, including asthma and other respiratory illnesses, renal diseases, dehydration, hypertension, and allergies.
Harlan et al., 2013 [41]USA: Maricopa County, Arizona
(Desert climate)		Observational—analytical2000–2008Vegetation
(Satellite imaging, objective measurement)		Mortality—Exposure and effects of excessive natural heat; and underlying causes of death: heat exposure, exhaustion, sun, heat stress, heat stroke, hyperthermia.
Heo et al., 2021 [42]USA: Connecticut, Pennsylvania, New Hampshire, New Jersey, New York, and Massachusetts
(Humid continental, and Humid subtropical climate)		Observational—analytic2000–2016Greenspace
(Satellite imaging, objective measurement)		Morbidity—Hospitalisations for all CVD and heatstroke.
Jang et al., 2020 [43]South Korea: Seoul
(Humid continental climate)		Observational—population-based time-series studyJune to September 2011–2017Eight district-level land use/land cover (LULC) indicators: woodland, crop-field, building, road, green coverage, wetland, impervious area, and urban forest, as percentages of total km2 area; detached houses or apartments.
(Satellite imaging, objective measurement)		Mortality—Heat-related mortality
Kim et al., 2020 [44] South Korea
(Humid subtropical and Humid continental climate)		Observational—time-series study June to September 2008–2017Housing quality and density
(Census tract, objective measurement)		Mortality—Heatwave-related mortality
Rosenthal et al., 2014 [45]USA: New York City
(Humid subtropical climate)		Observational—ecological1997–2006Housing conditions (dilapidated or deteriorating residential buildings, homes near structures rated good or excellent); AC ownership and usage; vegetation, impervious surfaces.
(Survey, Census tract, and Satellite imaging, objective measurement)		Mortality—Heat-related mortality, hypertension diagnosis, diabetes, self-reported general health status of fair/poor, obese, and current asthmatics.
Larrieu et al., 2008 [46]France: Gironde, Dordogne, Bordeaux, Dijon
(Oceanic climate)		Cross-sectional nested in two prospective cohorts.1–15 August 2003Accommodation characteristics: number of rooms;
floor level; possibility of ventilating; presence of AC and bedroom.
(Survey, objective measurement)		Morbidity—Hospitalisation and Mortality
Felt morbidity: whether subjects felt a deterioration of their health during the heat wave; and
Objective morbidity: (occurrence of a morbid outcome—dizzy spell, fall, loss of balance during the heatwave).
Lee et al., 2022 [13]USA: Cincinnati
(Humid continental climate)		Observational—analyticalJune to September 2016–2020Vegetation; surfaces; water bodies; urban structure (density, spatial structure [volume of the built-up area], normalized difference built-up index [NDBI] to measure the distribution of urban structure within the block groups); and percentage of pre-1939 houses.
(Satellite imaging and Census tract, objective measurement)		Morbidity—Ambulance Call-outs and Mortality—Heat-related call-outs for breathing problems, cardiac or respiratory arrest and death, chest pain, headache, heat exposure, stroke and CVD, and unconsciousness and fainting.
López-Bueno et al., 2020 [47]Spain: Madrid
(Semi-arid and Mediterranean climate)		Observational—Ecological, longitudinal retrospective time seriesJanuary 2010 to December 2013AC; aggregations of green zones including gardens, and historic and forest parks.
(Satellite imaging and Census tract, objective measurement)		Mortality—Heat-related mortality.
Madrigano et al., 2015 [48]USA: New York City
(Humid subtropical climate)		Observational—Case-only analysis2000–2011Built space; proportion covered by trees, grass/shrubs.
(Census tract, objective measurement)		Mortality—Underlying causes of death, particularly CVD, Myocardial infarction (MI), congestive heart failure (CHF), and Chronic obstructive pulmonary disease (COPD).
Naughton et al., 2002 [49]USA: Chicago
(Humid continental climate)		Observational—Case-control studyJuly–August 1999Top floor location of dwelling; AC
(Survey, objective measurement)		Mortality—Heart condition, heatstroke.
Ostro et al., 2010 [15]USA: California
(Mediterranean climate)		Time-stratified case-crossoverMay–September 1999–2005AC ownership and usage
(Survey, objective measurement)		Morbidity—Hospitalisation: Respiratory disease, Pneumonia, Asthma, COPD, CVD, Ischemic heart disease, Stroke, Ischemic stroke, MI, Heart failure, Dehydration, Heatstroke, Diabetes, Acute renal failure, Intestinal infection.
Schuster et al., 2017 [50]Germany: Berlin
(Oceanic climate)		Observational—Cross-sectionalAugust–September 2013 Building type; living and bedroom orientation; apartment level; perceived amount of urban green in neighbourhoods; accessibility of parks and open water.
(Survey, objective measurement)		Morbidity—Self-rated health, (medical) drug use, self-rated fitness.
Seong et al., 2022 [51]USA: Austin
(Humid subtropical climate)		ObservationalMay to September 2020 and 2021Impervious cover; tree canopy; pre-1980 housing; no AC; road density; water areas; and greenspace.
(Satellite imaging and Census tract, objective measurement)		Morbidity—Heat-related ambulance call-outs.
Son et al., 2016 [52]South Korea: Seoul
(Humid continental climate)		Observational—analyticalMay to September 2000–2009Urban vegetation
(Satellite imaging, objective measurement)		Mortality—All-cause mortality.
Uejio et al., 2011 [53]USA: Philadelphia and Phoenix
(Humid subtropical and desert climate)		EcologicalPhiladelphia: July–August 1999
Phoenix: June–September 2005		Vegetation health and density; impervious surface (%); housing density (houses/km2); single-family detached homes (%); age of house.
(Satellite imaging and Census tract, objective measurement)		Philadelphia: Mortality—extreme heat-related mortality, and Phoenix: Morbidity—Heat distress calls (ambulance call-outs).
Vandentorren et al., 2006 [14]France: Paris, Tours, and Orleans
(Oceanic climate)		Observational—Case-control8–13 August 2003 (peak of the heat wave)Housing conditions (related to building type, particular dwelling unit, and principal rooms, especially bedroom); Heat-island (calculated from mean of the surface temperature within 200 m radius area around each home and vegetative cover); Lack of thermal insulation; bedroom on the top floor; cooling techniques including fan or AC.
(Survey, Census tract and Satellite imaging, objective measurement)		Mortality—Cardiovascular or heat-related death (where the primary cause of death on certificates mentioned ‘dehydration’, ‘hyperthermia’ or ‘heat stroke’); Other causes included cancer, respiratory, and neurological diseases.
Vaneckova et al., 2010 [54]Australia: Sydney
(Humid subtropical climate)		Observational—analytical1 October–31 March for the period 1993–2004Percentage of vegetation; percentage of non-residential (built-up areas); percentage of non-typical dwellings.
(Census tract, objective measurement)		Mortality—All-cause mortality.
Wang C, et al., 2021 [55]USA: Maricopa County, Arizona
(Desert climate)		Observational—analytical2012–2016Surface reflectance; Normalized Difference Vegetation Index (NDVI).
(Satellite imaging, objective measurement)		Morbidity—Heat-related hospitalisation.
Wang Y, et al., 2016 [56]USA
(Semi-arid, Desert, Humid continental, Humid temperate, Humid subtropical, Mediterranean, Tropical, Oceanic, Subarctic, and Polar climate)		Ecological 1999–2010AC; NDVI
(Survey and Satellite imaging, objective measurement)		Morbidity—Heatstroke hospitalisation.
Williams et al., 2019 [57]USA: Cambridge
(Temperate climate)		Observational—Cross-sectional2015AC
(Survey, objective measurement)		Morbidity—Sleep disruption, galvanic skin response, heart rate.
Xu et al., 2013 [58]Spain: Barcelona
(Mediterranean climate)		Time-stratified case-crossover May–October 1999–2006AC; old building; surrounding greenness/tree cover
(Satellite imaging and Census tract, objective measurement)		Mortality—All-cause mortality.
Zanobetti et al., 2012 [59]USA
(Semi-arid, Desert, Humid continental, Humid temperate, Humid subtropical, Mediterranean, Tropical, Oceanic, Subarctic, and Polar climate)		Cohort 1985–2006Green surface
(Satellite imaging, objective measurement)		Mortality—Heat-related mortality.
Zuurbier et al., 2021 [60]Netherlands
(Oceanic climate)		Observational—Cross-sectional2012Type of dwelling; year built; surface area; height; floor location; green area
(Survey, objective measurement)		Morbidity—Self-perceived health.

3.2. Characteristics of Included Studies

The key characteristics of the included studies are presented in Table 1. Only eight of the 35 OECD Category 1 countries were represented in the 32 included studies. The majority (n = 17) focused on populations from one or more locations in the United States of America (USA) [13,15,34,35,37,38,39,41,42,45,48,49,51,55,56,57,59], with the remainder from South Korea [43,44,52,53], Canada [32,33], Australia [40,54], France [14,46], Spain [47,58], Germany [50], Netherlands [60], and Japan [36]. All the included studies were published between 2002 and 2024.
A total of 15 studies examined mortality data, which encompassed all-cause mortality and specific heat-related and chronic disease mortality data. Thirteen studies found a heat-related mortality association with vegetation and urban form [13,14,35,37,41,43,45,47,48,52,53,58,59]. Eight studies identified associations with housing characteristics [14,35,37,44,45,48,49,53], and three with air conditioning [45,47,49].
Eighteen studies explored heat-related morbidity through unscheduled hospitalisations [15,38,39,42,46,55,56], ambulance call-outs [13,51,53], and reporting of self-perceived health status [32,33,34,36,40,46,50,57,60]. The heat-related symptoms and health impacts included dizziness, nausea, vomiting, difficulty breathing, dehydration, headache, sleeplessness, mild and severe heat exhaustion, heat stroke, cardiovascular and cerebrovascular disease, respiratory and renal illnesses, diabetes, and intestinal infection. Some heat-related ambulance call-outs also included mortalities [13].
The most frequent associations between ambulance call-outs and built environment features related to vegetation and urban form [13,51,53], while hospitalisations had the most frequent associations with housing characteristics and/or air conditioning [15,38,39,46,56], followed by vegetation and urban form [42,55]. One study that examined extreme heat-related hospitalisations and vegetation found non-green spaces (i.e., areas not classified as open water, lawn, forest, shrubland, scrub, agricultural, grasses or wetlands) were not associated with vulnerability to extreme heat [38]. Studies examining self-reported health effects identified associations with features relating to vegetation and urban form [33,60], housing characteristics [34,50,60], and air conditioning [34,36,40,57].

3.3. Built Environment Features Associated with Heat-Related Health Outcomes Among Older People

Features of the built environment were categorised into three thematic groupings: (i) ‘Vegetation Coverage and Urban Form’, (ii) ‘Housing Characteristics’, and (iii) ‘Air Conditioning’. Vegetation coverage and urban form (including urban heat island, ground imperviousness, surface reflectance and walkability) were the most frequently examined in the included studies, followed in equal proportion by housing characteristics (such as type, age, building fabric, and condition), and the presence, type (e.g., central or window mounted), and use, of air conditioning. One-third of the included studies explored the association between a single built environment feature and heat-related morbidity or mortality, while the remaining two-thirds examined several features (Table 1). Table 2 summarises the main findings of this review. Further details can be found in the Supplementary Materials (Table S2).

3.3.1. Vegetation and Urban Form

Vegetation coverage and urban form have been combined into one group because they are both elements of the urban landscape that influence urban heat and surface temperatures [61] and, as such, have been explored together as contributing and counteracting factors in several included studies [13,14,43,51,53].
Nineteen of the included studies examined the association between vegetation and heat-related morbidity or mortality. This included tree canopy, trees, grass, shrubs, gardens, urban forests, parks, or wetlands [37,47,48,51]. Fifteen of the nineteen studies reported that the presence of vegetation reduced heat-related morbidity and/or mortality. The remaining four studies found no significant association between vegetation and heat-related health impacts. Specifically, these studies investigated associations between non-green space and extreme heat mortality [38], the level of vegetation and increased mortality during warmer months [54], residential greenery and heat impairment [50], and whether the vegetation index modified the association between heatwaves and heat stroke admissions [56]. Two studies suggested that the lack of association was likely due to data or measurement limitations [37,43].
Several studies in the USA and Korea found that higher urban vegetation could have a protective effect on the health of older people, including total mortality from higher temperatures [52], cardiovascular mortality during extreme heat events [37], human heat stress during hot days [41], and heat-related mortality resulting from the UHI (also referred to as urban heat anomaly) [43,45]. Conversely, for residents living in areas of Barcelona, Spain with little surrounding greenness, the impact of heat on mortality risk was significantly increased (RR = 1.29, 95% CI: 1.01–1.65) [58]. Moreover, a study of 135 cities in the USA found that for each 15% increase in green surface, mortality in hot temperatures amongst those with predisposing diseases such as myocardial infarction or chronic obstructive pulmonary disease was marginally reduced (Hazard Ratio [HR] = 0.98, 95% CI: 0.97–1.00) [59]. Heatwave mortality was assessed to be less likely amongst New York residents from areas with more grass and shrubs (OR = 0.96, 95% CI: 0.94–0.99) or where the proportion of trees was above the median value (OR = 0.97, 95% CI: 0.94–1.00) [48]. In Spain, green zones were associated with reduced heatwave mortality; however, the protective effect was not stronger than the use of air conditioning in homes [47].
Morbidity studies in the USA examined locations with higher vegetation and found there were reductions in heat-related morbidity [55], heat vulnerability [13], and heat-related ambulance call-outs [51]. Conversely, another study in northeast USA of 40 urban counties found the risk of heatstroke hospitalisations in areas with less vegetation had decreased over time (from RR = 2.7, 95% CI: 2.0–3.4 in 2000–2004) to (RR = 0.88, 95% CI: 0.31–2.53 in 2013–2016) [42]. This decline could be a result of greater efforts to adapt to higher temperature exposure and reduced hospitalisations.
Ten studies assessed features relating to urban form, including the UHI, which was associated with increased ambulance call-outs in the USA [53] and increased heatwave mortality among those aged 65 and over in Korea [43]. Other features of the urban form, including impervious surfaces (e.g., paved or unvegetated surfaces including roads, parking lots, and buildings), density and distribution of urban structures, were also associated with negative heat-related health conditions in the USA and France [13,14,48]. Two studies in the USA found the proportion of impervious surfaces to be a predictor of increased neighbourhood heat-related mortality rates [45], and a 0.8% increase in heat-related ambulance call-outs per one percent increase in the impervious area in a block group [51]. Higher surface temperature and reflectance were both found to contribute to higher heat-related morbidity in the USA [55]. However, two other studies found no association of urban form features with heatwave heatstroke admissions in the USA [56] or increased summer mortality in Australia [54].
Two studies examined walkability and access to public cooled spaces (e.g., public libraries, community centres, shopping malls) in socially disadvantaged neighbourhoods [35]. One study of populations drawn from the most materially and socially disadvantaged areas of Quebec, Canada, found that the areas with higher walkability were associated with increased adoption of adaptation behaviours to reduce negative heat-related health effects [33]. The other study, conducted in Arizona, USA, found heat-related mortality was marginally less likely to increase in socially vulnerable census areas, which provided more publicly accessible cooling spaces (IRR = 0.98, 95% CI 0.980–0.999). However, another study in the USA found the association was not evident in the case of all-cause mortality [35].

3.3.2. Housing Characteristics

There were 16 studies that explored housing characteristics, such as type (detached house or apartment), number of rooms, floor location of an apartment, and bedroom orientation. Thermal properties (assessed in one study by the number of hours an indoor temperature takes to increase from 25 to 32 °C in response to outside air temperature, and considering size, wall, and roof materials, including insulation) [35], as well as building fabric, insulation, and building condition, and their association with heat-related morbidity and/or mortality were also considered.
Dwellings with more rooms were associated with a reduced risk of heat-related mortality (OR = 0.85, 95% CI: 0.72–0.99) in France [14], and tenement dwellings (described as inferior blocks with four or fewer floors) were found to be associated with a higher heatwave-related mortality risk for older males living alone in South Korea [44]. However, the influence of socioeconomic factors should also be considered here. Top floor locations were found to be a risk factor for heat-related mortality [46,49,50] as well as the number of windows, and bedroom sun exposure [14]. Specifically, top-floor apartments, number of windows per 50 square metres, and amount of bedroom sun exposure significantly increased the risk of heat-related mortality (OR = 2.33, 95% CI: 1.33–4.09; OR = 1.19, 95% CI: 1.03–1.37; and OR = 1.07, 95% CI: 1.01–1.13, respectively) in France [14].
The age of dwellings and their association with heat-related illnesses were explored by seven studies [13,14,37,38,53,58,60]. Areas in Spain with large percentages of pre-1920 buildings were found to have a higher risk of heat-related mortality (RR = 1.21, 95% CI: 1.00–1.46) [58]. High percentages of pre-1940 housing in the USA were also associated with 9–15% increases in hospitalisations for extreme heat-related renal and respiratory illnesses [38]. Further, housing built before 1959 in the USA was found to be a potential effect modifier for extreme heat and cardiovascular mortality but not for respiratory mortality [37], and dwellings built before 1975 in France were associated with a higher risk of heatwave mortality than more recently built properties (OR = 1.83, 95% CI: 1.14–2.92) [14]. Neighbourhoods in Philadelphia, USA, with newer housing stock were associated with lower odds of heat-related mortality (OR = 0.93, 95% CI: 0.89–0.98) [53]. However, there was one study that found the percentage of housing built before 1939 was not a significant predictor of increased risk for heat-related ambulance call-outs in Cincinnati, USA [13], and another study in the Netherlands, examining heat-related morbidity, that found a slight decrease in indoor temperatures in older houses (built before 1930) compared to those built after 1985 [60].
Six studies assessed associations between heat-related morbidity and/or mortality in people aged 65 years and over, and the building fabric, including thermal protective properties. It was suggested that locations with buildings that took a longer time to heat up might have lower heat-related mortality (IRR = 0.92, 95% CI: 0.85–1.00) but higher all-cause mortality (IRR = 1.01, 95% CI: 1.00–1.02) for older people in the USA [35]. A lack of thermal insulation was found to be a risk factor for heatwave mortality in France [14]. Weatherisation was a statistically significant protective factor (OR = 0.695, 95% CI = [0.499–0.968]) for heat-related health symptoms in the USA [34]. Greater satisfaction with the quality of the thermal insulation of their dwelling and indoor temperatures in summer was associated with a self-reported reduction in adverse health outcomes [33]. However, it should be noted that other respondents perceived a deterioration in self-rated health and wellbeing when indoor temperatures exceeded 28 ◦C [40]. Poor housing quality and condition in New York were also found to increase mortality, although socioeconomic factors may have also played a role in contributing to the health outcome [45].

3.3.3. Air Conditioning

Seventeen of the included studies examined the association between heat-related morbidity or mortality and the presence, type, and frequency of use of air conditioning. Of these, five studies found moderating associations with the presence of air conditioning in the home [34,36,45,47,49]. Further, central air conditioning exhibited more pronounced cooling effects (in terms of differences between outdoor and indoor temperatures), compared to window units, which had a negative impact on residents’ experience of disrupted sleep, increased heart rates, and galvanic skin responses [57]. Central air conditioning in homes was also associated with a significant reduction in the risk of hospitalisations from higher temperatures in California [15], and a reduction in the risk of heat stroke admissions by 28% (9–43%) for each 10% increase in central air conditioning in homes across the USA [56]. A study in San Diego, USA, found a 14.6% increase in risk (95% CI: 4.5–24.6%) for hospitalisations during hot weather in coastal locations where air conditioning was less common, but no significant increase in inland locations with higher air conditioning presence [39]. However, a study in Austin, Texas, examining heat-related ambulance call-outs by census block groups (containing around 600 to 3000 residents), found the absence of air conditioning in dwellings was only significant during the summer month of August for heat-related ambulance call-outs [51].
In comparison, three other studies conducted in North America found no association between the presence of air conditioning in the home and heat-related morbidity [32], or mortality [35], and only a weak association with adaptation to heat [33]. Moreover, two European studies also found no significant association between air conditioning and heatwave mortality, both noting the relative rarity of residential air conditioning in northern Europe [14,58].

3.4. Quality of Evidence Assessment

The overall study quality assessed with the modified NIH tool was mainly rated as ‘good’ (21 studies), with the remainder all rated as ‘fair’ (11 studies). No studies were assessed as ‘poor’. These ‘fair’ quality studies were mainly downgraded due to issues relating to determining the sample power and details of exposure and their measurement, which in some cases was due to acknowledged data limitations [43,44,47]. A summary of the evidence assessment is available in the Supplementary Materials (Table S3).

4. Discussion

This systematic review of associations between built environment features and heat-related health outcomes in older, urban-dwelling people in high-income countries found that the role of vegetation and urban form in which the housing is located, housing characteristics, particularly the thermal insulation and building fabric, floor location, orientation, and age of the building, play an important role in the context of heat-related health.
Vegetation coverage and urban form have been treated as a single group in this review because of their roles in influencing urban heat and surface temperatures. As urbanisation has increased, vegetated areas, which have the potential to reduce urban heat by shading buildings and paved surfaces, evapotranspiration, and carbon sequestration, have often been replaced with impervious surfaces. These surfaces, especially buildings and roads, have been shown to have the greatest warming effects through lower albedo and greater absorption of solar radiation, exacerbating the UHI effect [61]. These opposing impacts were explored in several of the included studies [13,14,43,51,53].
Urban vegetation, especially trees [62], has a crucial role in mitigating adverse heat-related health impacts by facilitating evapotranspiration, which contributes to reducing the surface temperatures beneath trees, although the efficacy of this effect is diminished in areas characterised by high-rise buildings [63]. The greater role for trees, if strategically planted to maximise their effectiveness, is in providing shade to reduce direct solar exposure (to people and outdoor surfaces, including buildings) [63,64]. Moreover, tree canopy cover is one of several features that have been identified as ways to encourage walkability amongst older people [65], which in turn contributes to their general health and fitness, and is associated with reducing heat stress [50].
However, some studies examining measures to counteract the effects of the UHI, such as urban trees, have reported limitations in certain circumstances. In urban forms characterised by limited air circulation, trees with dense canopies providing daytime shade and reduced solar heat absorption may have the unintended consequence of contributing to higher nighttime temperatures due to restricting radiative cooling and trapping warm air [66]. In addition, it has been proposed that during drought periods, the cooling effects of trees may be diminished due to reduced evapotranspiration [63,67]. Overall, most of the included studies (n = 15) that examined the associations between vegetation and heat-related morbidity or mortality reported beneficial health outcomes.
Studies that reported an association with urban form, particularly focusing on the presence of larger impervious surfaces and rising surface temperatures [14,48,51,53], found a higher risk for potential heat-related morbidity or mortality. Urban centres in Cincinnati, USA, were found to have higher heat vulnerability and a greater number of heat-related health incidents than greener suburban areas [13]. Suburban locations and areas close to parks were proposed as a means to mitigate heat stress for individuals without access to air conditioning in the 1970s [18]. The removal of vegetation for suburban development has been reported as contributing to an increase in the rate of extreme heat events in sprawling cities [68]. Overall, amongst the included studies, the urban form of higher-density compact cities has been associated with heat-related morbidity and mortality [13,14,53,55].
Housing characteristics, especially top floor locations [14,49,50,60] and building age [14,37,38,53,58], showed significant associations with heat-related morbidity and mortality among older people. These findings are particularly important given the substantial amount of time older people may be spending in their homes. Studies have reported that citizens of developed countries spend most of their time (over 90%) indoors, including over 60% of this time in their homes, while the proportion for older people could be considerably greater, even 100% in some cases [69]. Some studies have identified the heat-related mortality associated with bedrooms located on the top floor [14]. Older people who spend extended time at home are also at higher risk from increased heat in their living spaces. A study conducted in the UK calculated that during a four-day heatwave, older people spent more than twice as much time in living areas with temperatures exceeding 28 ◦C, compared to younger families out at work and school [70].
The associations between building age and heat-related health outcomes varied across studies. Five of the included studies found associations between older buildings and increased heat-related morbidity and mortality [14,37,38,53,58], whereas another study revealed no significant association between building age and adverse health outcomes [13]. A study in the Netherlands examining older people and indoor heat exposure found lower temperatures in homes built before 1930 than in those built after 1985 [60]. A similar finding was reported in an earlier study of heat-related health effects, which found average bedroom temperatures in post-1980s UK homes were consistently higher than in older homes, especially pre-1919 detached homes with solid walls [71]. The inconsistent findings of these studies could be due to the thermal properties of houses, including insulation, that were associated with heatwave mortality [14,35,45] and morbidity [33,40]. Some older housing was constructed with thicker walls and ventilation designs suitable for summer without the installation of air conditioning. In contrast, modern housing typically features thinner walls but incorporates insulation materials and air conditioning systems. However, modern housing can also heat up quickly without appropriate cooling measures, such as turning on air conditioning. Moreover, studies have found that unless insulation is specifically designed to reduce the indoor effects of external heat, it can have the opposite effect. For example, internal wall insulation designed for colder climates can result in an increase in indoor temperatures in hot weather rather than a reduction [72,73,74].
Several other housing features, including external shutters and shading, passive ventilation, roof insulation, green roofs, cool pavements, and changes to surfaces to increase albedo, have demonstrated positive adaptive results in modelling and other research [11,34,69,75]. However, it is necessary to acknowledge that some of these features may have limitations. For example, while cool pavements and increasing albedo can contribute to reducing surface temperatures, they may also increase reflectance and glare from the sun for pedestrians during the day. Similarly, green roofs contribute to cooling (primarily by evapotranspiration), but they are only effective on lower-rise buildings and lack the reflectance advantage of cool roofs [63].
Air conditioning was identified as a significant moderating factor for heat-related health outcomes [34,36,45,47,49,56]. In fact, it has been suggested that air conditioning is the most protective measure against heat-related mortality [11]. However, it is important to note that air conditioning may have certain adverse impacts, including the inequity of access due to high capital costs and ongoing usage expenses. Moreover, the wide adoption of air conditioning contributes to the increasing energy demand during hot weather, thus potentially leading to power outages or rationing. Further, air conditioning can exacerbate greenhouse gas emissions if powered by fossil fuels. Measures to provide greater equity in the acquisition and operation of home air conditioning powered by renewably sourced energy would address these issues and improve heat-related health outcomes, particularly for older, vulnerable population groups. However, with the current design, the waste heat expelled from air conditioners adds to the effects of the UHI, particularly at night when it can increase the mean air temperature by up to 1 °C, potentially intensifying the demand for air conditioning use, and thus further expulsion of waste heat [11,15,39,53,76]. Therefore, despite the efficacy of air conditioning for reducing indoor temperatures and improving heat-related health, in its current form, the widespread use of air conditioning for personal indoor heat reduction may not be the most beneficial strategy compared to other less problematic options, such as increased shading, insulation and, where appropriate, remediation of impervious surfaces [11,69].
The impacts of these built environment features on heat health are not necessarily limited to older people. They impact all urban dwellers, workers and visitors, including other vulnerable groups such as the very young, those who are socioeconomically disadvantaged, those who are pregnant, those with chronic diseases and/or taking prescription drugs which impact the body’s heat regulation abilities, and those whose lifestyles make them more vulnerable to the health impacts of increasing heat such as outdoor workers, sportspeople, and recreational drug and alcohol users [77]. However, the focus of this review is people aged 65 and over, who are an increasing proportion of the population and who are more vulnerable to the impacts of the built environment features on heat health because their age impacts their bodies’ thermoregulatory abilities [10]. Moreover, older people may also have some of the aforementioned vulnerabilities of the general population, such as socioeconomic disadvantage, chronic illness, prescription or recreational drug use, as well as reduced mobility due to physical impairment and/or access to transport rendering them more likely to spend greater periods indoors or close to home. Additionally, it is worth noting that there was no obvious variation in the health impacts of key built environment features, such as vegetation, urban form, or housing characteristics, across different climate zones (Table 2). However, air conditioning appeared to be less effective in reducing heat-related health risks in cooler regions.
The limitations of this review should be acknowledged. First, we included older adults aged 65 years and over without considering the health behaviours of individual cases and ventilation efficiency of the dwellings. For example, whether older adults maintained adequate hydration levels by drinking more during the increased heat and/or the adequacy of the dwellings’ ventilation were not taken into account. Second, publication bias could be a potential limitation. Studies that found non-significant effects of built environment features on heat-related health risks might be less likely to be published. Given these limitations, the findings based on the published studies should be interpreted with caution, and further studies are warranted to replicate those findings on a larger scale and in different settings. Third, some studies used self-reported health conditions instead of objective measures or diagnoses, which may introduce potential inaccuracies to heat-related health outcomes. Moreover, a few studies also used the built environment features as proxies for socioeconomic disadvantage, which may reduce the transparency of associations and outcomes. Lastly, due to the considerable heterogeneity and diversity of the included studies and definitions of their data, measurements, and outcomes, more quantified results, including meta-analysis, could not be performed. Future studies should address shortcomings in data quality on relevant health and well-being matters within the context of the built environment. This may include accurate and time-relevant measurement of vegetation and urban form, air conditioning, and housing characteristics, as well as supporting deeper collaborations between urban planners, landscape and building architects, health professionals, medical researchers, and regulators to improve the resilience of urban areas and buildings in addressing heat-related health challenges in the context of climate change.

5. Conclusions

This study found housing characteristics, vegetation, and urban form features relating to the UHI had the most influence on heat-related health outcomes in older people. As older people spend considerable time indoors, measures to combat the UHI effect, such as increasing vegetation alone, may have limited effectiveness in reducing heat-related mortality. Thus, a more effective approach would involve a combination of improved housing, vegetation, and urban form features. This could include measures to remediate impervious surfaces and target housing characteristics such as thermal protection and building fabric, and upper-storey shading and insulation, to effectively support the widespread adaptation to increasing heat and the mitigation of heat-related adverse health impacts in older people. This approach would better protect the health and well-being of older people in the face of increasing heat and facilitate the positive contribution of vegetation to heat adaptation, physical activity, social interaction, and overall population health.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/greenhealth1010002/s1, Table S1: Covidence customized spreadsheet, column headings including those used for quality assessment; Table S2: Details for analysis extracted from Covidence customized spreadsheet; Table S3: Summary of evidence grading.

Author Contributions

S.S. was involved in the conceptualisation and design of the study, literature search, screening, data collection, analysis, interpretation, and manuscript writing. M.T. was involved in the conceptualisation and design of the study, literature search, screening, data collection, analysis, interpretation, editing, and review of the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Ethics approval was not needed as the systematic literature review used previously published data from scientific journals.

Data Availability Statement

Data used in this systematic literature review are available publicly in the original published journal articles.

Acknowledgments

We gratefully acknowledge the ANU National Centre for Epidemiology and Population Health for supporting this study.

Conflicts of Interest

The authors declare that they have no known competing interests.

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Figure 1. PRISMA flowchart for literature search and selection process following PRISMA guidelines.
Figure 1. PRISMA flowchart for literature search and selection process following PRISMA guidelines.
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Table 2. Summary of the main findings.
Table 2. Summary of the main findings.
Built Environment FeatureNumber of StudiesMain Findings
Vegetation and Urban Form (Surfaces, UHI, walkability to public cooling space)22
  • Fifteen studies found the presence of vegetation reduced heat-related morbidity [13,42,51,55,60] and/or mortality [14,37,41,43,45,47,48,52,58,59] in Oceanic, Humid continental, Humid subtropical, Humid temperate, Desert, Semi-arid, Mediterranean, Tropical, Subarctic, and Polar climate zones. Of these, two found that in some situations, vegetation had an insignificant or indirect effect on mitigating heat effects [37,43] in a Humid continental climate. Four other studies found no significant association between vegetation and heat-related morbidity and/or mortality [38,50,54,56] in Oceanic, Humid continental, Humid subtropical, Humid temperate, Desert, Semi-arid, Mediterranean, Tropical, Subarctic, and Polar climate zones.
  • Eight studies found that aspects of the urban form increased heat-related mortality [14,43,45,48] and morbidity [13,51,53,55] in Oceanic, Humid continental, Humid subtropical, and Desert climate zones. However, two other studies found no association of urban form features with heatwave heatstroke admissions [56] or increased summer mortality [54] in Oceanic, Humid continental, Humid subtropical, Humid temperate, Desert, Semi-arid, Mediterranean, Tropical, Subarctic, and Polar climate zones.
  • One study found neighbourhood walkability reduced heat-related morbidity [33], and another study found that access to public cooling spaces reduced heat-related mortality [35] in Desert, Arctic, Subarctic, and Humid continental climate zones.
Housing Characteristics—type, age, fabric, thermal properties, condition 16
  • Sixteen studies found an association between housing characteristics and heat-related morbidity and/or mortality; in particular:
    ○
    more rooms were associated with a reduced risk of heat-related mortality [14,44] in Oceanic, Humid subtropical, and Humid continental climate zones, and poor inferior quality dwellings were found to be associated with a higher heatwave-related mortality risk for older males living alone [44] in Humid subtropical and Humid continental climate zones.
    ○
    top floor locations, orientation, and number of windows were risk factors for heat-related mortality [14,46,49,50,60] in Oceanic and Humid continental climate zones.
    ○
    older housing was associated with increased heat-related mortality [14,37,53,58] and hospitalisations [38] in Oceanic, Humid continental, Humid subtropical, Humid temperate, Desert, Semi-arid, Mediterranean, Tropical, Subarctic, and Polar climate zones. However, one study found no association between older housing and heat-related ambulance call-outs [13] and another, examining heat-related morbidity, found a slight decrease in temperatures [60] in Humid continental and Oceanic climate zones.
    ○
    dwellings’ thermal protective properties, insulation and housing condition were found to have associations with heatwave mortality [14,35,45] and morbidity [33,34,40] in Oceanic, Desert, Arctic, Subarctic, Humid continental, Humid subtropical, and Mediterranean climate zones.
Air conditioning (AC)17
  • Twelve studies reported that air conditioning had positive outcomes on heat-related morbidity [15,34,36,39,40,46,51,56,57] and/or mortality [45,47,49] in Mediterranean, Humid subtropical, Humid continental, Humid temperate, Tropical rainforest, Temperate, Semi-arid, Desert, Oceanic, Subarctic, and Polar climate zones.
  • Three North American studies found no association between the presence of air conditioning in the home and heat-related morbidity [32] or mortality [35] in Humid continental and Desert climate zones, and only a weak association with adaptation to heat [33] in Arctic, Subarctic, and Humid continental climate zones.
  • Two European studies also found no significant association between heatwave mortality and air conditioning, both noting the relative rarity of residential air conditioning in Europe [14,58] in Oceanic and Mediterranean climate zones.
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Strickland, S.; Tong, M. What Are the Key Built Environment Features Associated with Heat-Related Health Risks Among Older People in High Income Countries? Green Health 2025, 1, 2. https://doi.org/10.3390/greenhealth1010002

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Strickland S, Tong M. What Are the Key Built Environment Features Associated with Heat-Related Health Risks Among Older People in High Income Countries? Green Health. 2025; 1(1):2. https://doi.org/10.3390/greenhealth1010002

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Strickland, Susan, and Michael Tong. 2025. "What Are the Key Built Environment Features Associated with Heat-Related Health Risks Among Older People in High Income Countries?" Green Health 1, no. 1: 2. https://doi.org/10.3390/greenhealth1010002

APA Style

Strickland, S., & Tong, M. (2025). What Are the Key Built Environment Features Associated with Heat-Related Health Risks Among Older People in High Income Countries? Green Health, 1(1), 2. https://doi.org/10.3390/greenhealth1010002

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