Risk Of Heat-related Mortality Research Articles

Vulnerability to heat-related mortality and the effect of prevention measures: a time-stratified case-crossover study in Switzerland

BACKGROUND: Swiss climate scenarios predict increases in the frequency and intensity of extreme heat episodes in the future. For the effective prevention of heat-related mortality, several aspects of the population’s vulnerability to heat must be understood on a local level. METHODS: A nationwide analysis of individual death records was conducted, enabling a more comprehensive understanding than typical heat studies based on aggregated data. A total of 320,306 individual death records from the Swiss National Cohort with precise address information during the warm season (May to September) from 2003–2016 were linked to indoor and outdoor high-resolution daily temperature estimates. A time-stratified case-crossover study combined with distributed lag non-linear models was then performed to assess the temperature-mortality associations for various causes of death and to estimate the potential effect modification of individual characteristics. Additionally, it was explored whether the effect of extreme heat changed over time in regions with and without cantonal heat-health action plans (HHAPs). RESULTS: Using the temperature with the lowest cause-specific mortality risk (minimum mortality temperature) as the reference temperature, extreme heat (defined as ambient daily maximum temperature reaching 33 °C) was associated with a strong increase in all-cause mortality (odds ratio (OR): 1.21, 95% CI: 1.17–1.25) and disease-specific mortality from Alzheimer’s disease and dementia (OR: 1.67, 95% CI: 1.48–1.88), COPD (OR: 1.37, 95% CI: 1.12–1.67), diabetes (OR: 1.34, 95% CI: 1.06–1.70), and myocardial infarction (OR: 1.26, 95% CI: 1.10–1.44). Indoor temperatures above 24 °C were found to be critical for mortality. The population most vulnerable to heat included older adults (≥75 years), unmarried individuals, people with a low education level, older women with low neighbourhood socioeconomic position, and men under 75 years old with low socioeconomic position. Overall, the risk of heat-related all-cause mortality in 2009–2016 was lower than that in 2003–2008. The decrease was significantly stronger in the region where cantonal HHAPs were implemented. CONCLUSIONS: This study provides important information for planning targeted and effective measures to reduce heat-related health risks in Switzerland. It demonstrates that HHAPs contribute to reducing heat-related mortality, although they may not reach the high-risk population of individuals with low socioeconomic position. Future prevention efforts should also target the less privileged population, including people younger than 75 years.

Spatiotemporal Facility-Level Patterns of Summer Heat Exposure, Vulnerability, and Risk in United States Prison Landscapes.

Heat is associated with increased risk of morbidity and mortality. People who are incarcerated are especially vulnerable to heat exposure due to demographic characteristics and their conditions of confinement. Evaluating heat exposure in prisons, and the characteristics of exposed populations and prisons, can elucidate prison-level risk to heat exposure. We leveraged a high-resolution air temperature data set to evaluate short and long-term patterns of heat metrics for 1,614 prisons in the United States from 1990 to 2023. We found that the most heat-exposed facilities and states were mostly in the Southwestern United States, while the prisons with the highest temperature anomalies from the historical record were in the Pacific Northwest, the Northeast, Texas, and parts of the Midwest. Prisons in the Pacific Northwest, the Northeast, and upper Midwest had the highest occurrences of days associated with an increased risk of heat-related mortality. We also estimated differences in heat exposure at prisons by facility and individual-level characteristics. We found higher proportions of non-white and Hispanic populations in the prisons with higher heat exposure. Lastly, we found that heat exposure was higher in prisons with any of nine facility-level characteristics that may modify risk to heat. This study brings together distinct measures of exposure, vulnerability, and risk, which would each inform unique strategies for heat-interventions. Community leaders and policymakers should carefully consider which measures they want to apply, and include the voices of directly impacted people, as the differing metrics and perspectives will have implications for who is included in fights for environmental justice.

Association between Heat Vulnerability Index and Stroke Severity.

Socioeconomically disadvantaged neighborhoods are particularly vulnerable to heat-related illnesses. We aim to investigate the association between the heat vulnerability index (HVI), an established neighborhood-level metric of heat-related mortality risk, and acute ischemic stroke (AIS) severity. We conducted a retrospective analysis of consecutive AIS admissions to a comprehensive stroke center between 2012 and 2021. Stroke severity was defined upon admission based on the National Institutes of Health Stroke Scale (NIHSS). Demographic, socioeconomic, and clinical characteristics were extracted from electronic health records. HVI status was assigned using residential ZIP codes. Multivariable logistic regression analyses were performed. Of 3429 AIS admissions, 1123 (32.8%) were from high-HVI (scores 4-5) neighborhoods and 868 (25.3%) had severe stroke (NIHSS score ≥ 10). In the multivariable regression model with stepwise selection, a high HVI was independently associated with severe stroke (adjusted odds ratio: 1.40 [95% confidence interval 1.16-1.69]). The association between a high HVI and severe stroke underscores the importance of targeting policy interventions to mitigate heat-related illness in socioeconomically disadvantaged neighborhoods.

Do greenspaces really reduce heat health impacts? Evidence for different vegetation types and distance-based greenspace exposure

BackgroundWhile vegetation type, population density and proximity to greenspaces have been linked to human health, what type and location of greenspace matter most have remained unclear. In this context, there are question marks over investment-style metrics. ObjectivesThis paper aims at establishing what vegetation type may matter most in modifying heat-mortality associations, and what the optimal buffer distances of total and specific types of greenspace exposure associated with reduced heat-related mortality risks are. MethodsWe conducted small-area analyses using daily mortality data for 286 Territory Planning Units (TPUs) across Hong Kong and 1 × 1 km gridded air temperature data for the summer months (2005–2018). Using a case time series design, we examined effect modifications of total and specific types of greenspaces, as well as population-weighted exposure at varying buffer distances (200–4000 m). We tested the significance of effect modifications by comparing relative risks (RRs) between the lowest and highest quartiles of each greenspace exposure metric; and explored the strength of effect modifications by calculating the ratio of RRs. ResultsForests, unlike grasslands, showed significant effect modifications on heat-mortality associations, with RRs rising from 0.98 (95 %CI: 0.92,1.05) to 1.06 (1.03, 1.10) for the highest to lowest quartiles (p-value = 0.037) The optimal distances associated with the most apparent effects were around 1 km for population-weighted exposure, with the ratio of RRs being 1.424 (1.038,1.954) for NDVI, 1.191 (1.004,1.413) for total greenspace, and 1.227 (1.024,1.470) for forests. A marked difference was observed in terms of the paired area-level and optimal distance-based exposure to total greenspace and forests under extreme heat (p-values < 0.05). DiscussionOur findings suggest that greenspace, particularly nearby forests, may significantly mitigate heat-related mortality risks.

Effect Modification of Heat-Related Mortality Risk by Air Pollutants in Shandong, China.

Although studies have reported the modification effect of air pollutants on heat-related health risk, little is known on the modification effect among various particulate matter with different particle size on mortality. We aimed to investigate whether the associations of hot temperatures with daily mortality were modified by different air pollutant levels in Shandong Province, China. Daily data of air pollutants, meteorological factors, and mortality of 1,822 subdistricts in Shandong province from 2013 to 2018 were collected. We used a time-stratified case-crossover model with an interaction term between the cross-basis term for ambient temperature and the linear function of particulate matter ≤1 µm (PM1), PM2.5, nitrogen dioxide (NO2), and ozone to obtain heat-mortality associations during the hot season. Results showed that the cumulative odds ratio of extreme heat on mortality over 0 to 10 days was 3.66 (95% CI: 3.10-4.31). The mortality risk during hot seasons was stronger at high air pollutant levels. The modification effect of particulate matters on heat-related mortality decreased by its aerodynamic diameter. Females and older adults over 75 years were more vulnerable to the modification effect of air pollutants, and significant differences were detected in the association between temperatures and mortality stratified by PM1 and PM2.5. Higher heat-related mortality risks were observed at high NO2 levels, especially for cardiorespiratory disease. The findings suggest that more consideration should be given to the combined effect of very fine particles and NO2 with ambient heat when developing healthcare strategies, and women and older adults should be given priority in health-related settings.

Extreme Temperatures and Stroke Mortality: Evidence From a Multi-Country Analysis.

Extreme temperatures contribute significantly to global mortality. While previous studies on temperature and stroke-specific outcomes presented conflicting results, these studies were predominantly limited to single-city or single-country analyses. Their findings are difficult to synthesize due to variations in methodologies and exposure definitions. Within the Multi-Country Multi-City Network, we built a new mortality database for ischemic and hemorrhagic stroke. Applying a unified analysis protocol, we conducted a multinational case-crossover study on the relationship between extreme temperatures and stroke. In the first stage, we fitted a conditional quasi-Poisson regression for daily mortality counts with distributed lag nonlinear models for temperature exposure separately for each city. In the second stage, the cumulative risk from each city was pooled using mixed-effect meta-analyses, accounting for clustering of cities with similar features. We compared temperature-stroke associations across country-level gross domestic product per capita. We computed excess deaths in each city that are attributable to the 2.5% hottest and coldest of days based on each city's temperature distribution. We collected data for a total of 3 443 969 ischemic strokes and 2 454 267 hemorrhagic stroke deaths from 522 cities in 25 countries. For every 1000 ischemic stroke deaths, we found that extreme cold and hot days contributed 9.1 (95% empirical CI, 8.6-9.4) and 2.2 (95% empirical CI, 1.9-2.4) excess deaths, respectively. For every 1000 hemorrhagic stroke deaths, extreme cold and hot days contributed 11.2 (95% empirical CI, 10.9-11.4) and 0.7 (95% empirical CI, 0.5-0.8) excess deaths, respectively. We found that countries with low gross domestic product per capita were at higher risk of heat-related hemorrhagic stroke mortality than countries with high gross domestic product per capita (P=0.02). Both extreme cold and hot temperatures are associated with an increased risk of dying from ischemic and hemorrhagic strokes. As climate change continues to exacerbate these extreme temperatures, interventional strategies are needed to mitigate impacts on stroke mortality, particularly in low-income countries.

Assessing the role of socio-economic factors in shaping the temperature-mortality exposure-response relationship in China

Non-optimal temperatures significantly influence public health. However, the role of socio-economic factors in modulating health risks associated with non-optimal temperatures varies geographically and among different populations. Thus, the meteorological, air quality, health data, and socio-economic indicators were obtained from 23 districts in North and 48 districts in East China, respectively. Employing a two-stage meta-analysis, the exposure-response relationship was constructed for temperature against mortality from non-accidental causes, cardiovascular and cerebrovascular diseases, and respiratory illnesses. Furthermore, a non-linear spline regression was applied to assess the impact of socio-economic indicators on the exposure-response relationship and predicted future risks under various Shared Socioeconomic Pathways. The results revealed that the influence of socio-economic factors on the exposure-response curve showed heterogeneity in East China and North China. In North China, the shape of the exposure-response curve changed greatly under different socio-economic levels, while it remained similar in East China. In East China, the relative risk of heat and cold exposure was reduced in regions with high GDP, high levels of public finance, good medical services, and a low proportion of the elderly population. Specifically, the risk of non-accidental deaths due to heat shows a nearly linear negative correlation with per capita GDP in East China, with a decrease of the relative risk by 0.075 for every 10 thousand yuan increase in per capita GDP. Future projections indicate that population aging plays a decisive role in shaping the exposure-response curves. Although economic growth can reduce the risk of heat-related mortality, the combined effect of population aging and economic increase results in steeper exposure-response curves in both hot and cold temperature ranges in the future. In conclusion, although spatial variations in relative risk changes still exist, enhancing the adaptive capacity of populations can mitigate health risks associated with future climate change.

A study on the monitoring of heatwaves and bivariate frequency analysis based on mortality risk assessment in Wuhan, China.

The increasingly frequent occurrence of urban heatwaves has become a significant threat to human health. To quantitatively analyze changes in heatwave characteristics and to investigate the return periods of future heatwaves in Wuhan City, China, this study extracted 9 heatwave definitions and divided them into 3 mortality risk levels to identify and analyze historical observations and future projections of heatwaves. The copula functions were employed to derive the joint distribution of heatwave severity and duration and to analyze the co-occurrence return periods. The results demonstrate the following. (1) As the concentration of greenhouse gas emissions increases, the severity of heatwaves intensifies, and the occurrence of heatwaves increases significantly; moreover, a longer duration of heatwaves correlated with higher risk levels in each emission scenario. (2) Increasing concentrations of greenhouse gas emissions result in significantly shorter heatwave co-occurrence return periods at each level of risk. (3) In the 3 risk levels under each emission scenario, the co-occurrence return periods for heatwaves become longer as heatwave severity intensifies and duration increases. Under the influence of climate change, regional-specific early warning systems for heatwaves are necessary and crucial for policymakers to reduce heat-related mortality risks in the population, especially among vulnerable groups.

Exploring the contribution of inter-individual factors to the development of physiological heat strain in older adults exposed to simulated indoor overheating.

Older adults are at elevated risk of heat-related mortality due to age-associated declines in thermoregulatory and cardiovascular function. However, the inter-individual factors that exacerbate physiological heat strain during heat exposure remain unclear, making it challenging to identify more heat-vulnerable subgroups. We therefore explored factors contributing to inter-individual variability in physiological responses of older adults exposed to simulated hot weather. Thirty-seven older adults (61-80 years, 16 females) rested for 8 h in 31 and 36 °C (45% relative humidity). Core (rectal) temperature, heart rate (HR), HR variability, mean arterial pressure (MAP), and cardiac autonomic responses to standing were measured at baseline and end-exposure. Bootstrapped least absolute shrinkage and selection operator regression was used to evaluate whether variation in these responses was related to type 2 diabetes (T2D, n=10), hypertension (n=18), age, sex, body morphology, habitual physical activity levels, and/or heat-acclimatization. T2D was identified as a predictor of end-exposure HR (with vs. without: 13 beats/min (bootstrap 95% confidence interval: 6, 23)), seated MAP (-7mmHg (-18, 1)), and the systolic pressure response to standing (20mmHg (4, 36)). HR was also influenced by sex (female vs. male: 8 beats/min (1, 16)). No other predictors were identified. The inter-individual factors explored did not meaningfully contribute to the variation in body temperature responses in older adults exposed to simulated indoor overheating. By contrast, cardiovascular responses were exacerbated in females and individuals with T2D. These findings improve understanding of how inter-individual differences contribute to heat-induced physiological strain in older persons.

Age-Related Differences in the Onset of Cardiovascular Drift during Progressive Heat Stress (PSU HEAT Project)

As a result of the increasing duration, frequency, and severity of heat waves, older men and women are at greater risk for heat-related morbidity and mortality, with the majority of excess heat-related deaths attributed to increased cardiovascular strain associated with heat stress. PURPOSE: To (1) identify the environmental conditions (ambient temperature (Tdb) and humidity (rh)) at which heart rate (HR) begins to increase from equilibrium (i.e., the onset of cardiovascular drift), and (2) compare the environments in which cardiovascular drift begins relative to those at which a continuous rise in core temperature (Tc) is observed in young (Y), middle (MA), and older (O) adults. Methods: 26 Y (10 F; 19-29 yrs), 27 MA (21F; 40-64 yrs), and 19 O (7 F; 65-76 yrs) subjects were exposed to progressive heat stress in an environmental chamber at a low metabolic rate reflecting activities of daily living (159 ± 34 W) in a warm-humid (WH, 34-36°C, 50-80% rh) and a hot-dry (HD, 38°C-52°C, &lt;30% rh) environment. The environmental thresholds above which HR and Tc equilibrium could no longer be maintained were identified. Results: In WH environments, sustained increases in HR preceded the Tc inflection point in Y (73±5% rh vs. 81±5% rh; p&lt;0.001), MA (67±11% rh vs. 73±12% rh; p&lt;0.001), and O adults (53±11% rh vs. 57±12% rh; p=0.041). Similarly, in HD (15-20% rh) environments, the onset of cardiovascular drift preceded the Tc inflection point in Y (47±3°C vs. 49±3°C; p=0.004), MA (44±4°C vs. 46±4°C; p&lt;0.001), and O adults (42±5°C vs. 44±4°C; p=0.007). Additionally, in WH environments, cardiovascular drift began at lower combinations of Tdb and rh in O vs. Y subjects (34°C, 53±11% rh vs. 34°C, 73±5% rh; p&lt;0.001) and O vs. MA adults (34°C, 53±11% rh vs. 34°C, 67±11% rh; p=0.008). In HD environments, cardiovascular drift began at lower environments in MA vs. Y (44±4°C, 18% rh vs. 47±3°C, 15% rh; p=0.044) and O vs. Y (42±5°C, 20% rh vs. 47±3°C, 15% rh; p=0.006) CONCLUSION: These data suggest that cardiovascular drift, indicating increases in cardiovascular strain, occurs during compensable heat stress at metabolic rates reflecting activities of daily living in Y, MA, and O adults. Further, there is an age-associated shift in the onset of cardiovascular drift toward lower combinations of Tdb and rh. SIGNIFICANCE/NOVELTY: These results are the first to identify the specific environmental conditions at which increases in cardiovascular strain occur across the adult age spectrum. These findings provide concrete data for the development of safety guidelines and policy decisions to mitigate cardiovascular-related morbidity and mortality during impending heat events. Supported by NIA Grant T32 AG049676 (to R.M.C.) and NIH Grant R01 AG067471 (to W.L.K.). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Influence of home-based heat therapy on thermal and cardiovascular strain during passive heat exposure in older adults

Heat waves are occurring more frequently and with greater intensity. In fact, 2023 marked the hottest summer ever recorded in the Northern Hemisphere. Heat waves increase the risk for heat-related morbidity and mortality, particularly for older adults who have a reduced ability to dissipate heat. Heat acclimation induces physiological adaptations that attenuate thermal and cardiovascular strain during subsequent heat exposures. However, traditional heat acclimation protocols require expensive equipment (e.g., climate chamber) and may be challenging for older adults with limited functional capacity. Home-based heat therapy provides a potentially safe and pragmatic option to induce heat acclimation. The purpose of this pilot study was to test the hypothesis that home-based heat therapy reduces thermal and cardiovascular strain in older adults during acute passive heat exposure. Six older adults (5 women; 67 ± 4 years) performed 8 weeks of home-based heat therapy by immersing their lower legs ~33 cm into a heated (~ 42°C) and circulated water bath 4 days per week, for 45 min per session. Intestinal temperature (telemetric pill) and heart rate were assessed before (pre) and after (post) the intervention during acute heat exposure (45 min lower leg water immersion). In addition, rate pressure product, an estimate of myocardial demand, was calculated as heart rate x systolic blood pressure. Resting intestinal temperature, heart rate, and rate pressure product did not differ from pre to post heat therapy (all P ≥ 0.6). However, the change in intestinal temperature during acute heat exposure was reduced after heat therapy (15 min: pre, Δ0.47 ± 0.17 °C vs. post, Δ0.33 ± 0.14 °C; 30 min: pre, Δ0.84 ± 0.29 °C vs. post, Δ0.72 ± 0.23 °C; 45 min: pre, Δ1.10 ± 0.27 °C vs. post, Δ1.07 ± 0.24 °C; P = 0.03 for main effect of time). Likewise, the change in heart rate was attenuated following the intervention (15 min: pre, Δ14 ± 9 bpm vs. post, Δ10 ± 5 bpm; 30 min: pre, Δ22 ± 13 bpm vs. post, Δ17 ± 6 bpm; 45 min: pre, Δ25 ± 9 bpm vs. post, Δ21 ± 6 bpm; P = 0.02 for main effect of time). Rate pressure product was also reduced following heat therapy (15 min: pre, Δ1280 ± 1636 bpm·mmHg vs. post, Δ322 ± 698 bpm·mmHg; 30 min: pre, Δ1800 ± 1573 bpm·mmHg vs. post, Δ1170 ± 450 bpm·mmHg; 45 min: pre, Δ2145 ± 593 bpm·mmHg vs. post, Δ840 ± 602 bpm·mmHg; P &lt; 0.01 for main effect of time). Our preliminary data suggest that 8 weeks of home-based heat therapy elicits some adaptations that may reflect heat acclimation. However, further work is needed to confirm these initial findings. American Heart Association TPA958179. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Cooling and optimizing urban heat island based on a thermal knowledge-informed multi-type ant colony model

In the context of rapid urbanization and global warming, the urban heat island (UHI) intensifies the risk of heat-related mortality, endangering the health of urban residents. Urban greening effectively mitigates severe urban heating climates, but increasing green space without restrictions is undesirable due to the scarcity of urban land. Accurately characterizing the scope and intensity of UHI and determining the spatial location of the area that needs to be optimized are necessary. In this study, an inverse S-shaped function was used to fit the urban-rural temperature attenuation, whose parameters explicitly describe the properties of UHI. Additionally, a thermal knowledge-informed multi-type ant colony model was proposed to cool UHI automatically. A case study of Wuhan showed that: (1) the fitting effect of the inverse S-shaped function is desirable with the adjusted R2 exceeding 0.97, and the derived parameters with clear physical meanings avoid subjectivity in describing thermal characteristics; (2) high-level heat island of the main urban areas can be reduced by 7.7%–8.5% after land use optimization; and (3) a comparison with the traditional multi-type ant colony model verifies that the model proposed in this study can avoid excessive dispersion of the optimized pixels whose land use types are modified and achieve more reasonable and stable optimization results. This study provides useful exploratory tools for sustainable urban planning, heat mitigation solutions, and other urban retrofitting.

Intensifying human-driven heatwaves characteristics and heat related mortality over Africa

Heatwaves in Africa are expected to increase in frequency, number, magnitude, and duration. This is significant because the health burden is only expected to worsen as heatwaves intensify. Inadequate knowledge of the climate’s impact on health in developing nations such as Africa makes safeguarding the health of vulnerable groups at risk challenging. In this study, we quantify possible roles of human activity in heatwave intensification during the historical period, and project the future risk of heat-related mortality in Africa under two Representative Concentration Pathways (RCP26) and (RCP60). Heatwaves are measured using the Excess Heat Factor (EHF); the daily minimum (Tn ) and maximum (Tx ) are used to compute the EHF index; by averaging Tx and Tn . Two heat factors, significance and acclimatization are combined in the EHF to quantify the total excess heat. Our results confirm the intensification of heatwaves across Africa in recent years is due anthropogenic activity (increase in greenhouse gas concentration and changes in land use). The Return event highlights the potential future escalation of heatwave conditions brought on by climate change and socioeconomic variables. RCP26 projects a substantial rise in heat-related mortality, with an increase from about 9000 mortality per year in the historical period to approximately 23 000 mortality per year at the end of the 21st century. Similarly, RCP60 showed an even more significant increase, with heat-related mortality increasing to about 43 000 annually. This study highlights the potentially growing risk of intensifying heatwaves in Africa under different emission scenarios. It projects a significant increase in heatwave magnitude, number, duration, frequency, and heat-related mortality. Africa’s low adaptive capacity will amplify the impact, emphasizing the need for emissions reduction and effective adaptation measures.

Socio-environmental modifiers of heat-related mortality in eight Swiss cities: A case time series analysis

In the light of growing urbanization and projected temperature increases due to climate change, heat-related mortality in urban areas is a pressing public health concern. Heat exposure and vulnerability to heat may vary within cities depending on structural features and socioeconomic factors. This study examined the effect modification of the temperature-mortality association of three socio-environmental factors in eight Swiss cities and population subgroups (<75 and ≥ 75 years, males, females): urban heat islands (UHI) based on within-city temperature contrasts, residential greenness measured as normalized difference vegetation index (NDVI) and neighborhood socioeconomic position (SEP). We used individual death records from the Swiss National Cohort occurring during the warm season (May to September) in the years 2003–2016. We performed a case time series analysis using conditional quasi-Poisson and distributed lag non-linear models with a lag of 0–3 days. As exposure variables, we used daily maximum temperatures (Tmax) and a binary indicator for warm nights (Tmin ≥20 °C).In total, 53,593 deaths occurred during the study period. Overall across the eight cities, the mortality risk increased by 31% (1.31 relative risk (95% confidence interval: 1.20–1.42)) between 22.5 °C (the minimum mortality temperature) and 35 °C (the 99th percentile) for warm-season Tmax. Stratified analysis suggested that the heat-related risk at 35 °C is 26% (95%CI: −4%, 67%) higher in UHI compared to non-UHI areas. Indications of smaller risk differences were observed between the low vs. high greenness strata (Relative risk difference = 13% (95%CI: −11%; 44%)). Living in low SEP neighborhoods was associated with an increased heat related risk in the non-elderly population (<75 years). Our results indicate that UHI are associated with increased heat-related mortality risk within Swiss cities, and that features beyond greenness are responsible for such spatial risk differences.

Physiological responses to 9 hours of heat exposure in young and older adults. Part III: Association with self-reported symptoms and mood state.

Older adults are at greater risk of heat-related morbidity and mortality during heat waves, which is commonly linked to impaired thermoregulation. However, little is known about the influence of increasing age on the relation between thermal strain and perceptual responses during daylong heat exposure. We evaluated thermal and perceptual responses in 20 young (19-31 yr) and 39 older adults (20 with hypertension and/or type 2 diabetes; 61-78 yr) resting in the heat for 9 h (heat index: 37°C). Body core and mean skin temperature areas under the curve (AUC, hours 0-9) were assessed as indicators of cumulative thermal strain. Self-reported symptoms (68-item environmental symptoms questionnaire) and mood disturbance (40-item profile of mood states questionnaire) were assessed at end-heating (adjusted for prescores). Body core temperature AUC was 2.4°C·h [1.0, 3.7] higher in older relative to young adults (P < 0.001), whereas mean skin temperature AUC was not different (-0.5°C·h [-4.1, 3.2] P = 0.799). At end-heating, self-reported symptoms were not different between age groups (0.99-fold [0.80, 1.23], P = 0.923), with or without adjustment for body core or mean skin temperature AUC (both P ≥ 0.824). Mood disturbance was 0.93-fold [0.88, 0.99] lower in older, relative to young adults (P = 0.031). Older adults with and without chronic health conditions experienced similar thermal strain, yet those with these conditions reported lower symptom scores and mood disturbance compared with young adults and their age-matched counterparts (all P ≤ 0.026). Although older adults experienced heightened thermal strain during the 9-h heat exposure, they did not experience greater self-reported symptoms or mood disturbance relative to young adults.NEW & NOTEWORTHY Despite experiencing greater cumulative thermal strain during 9 h of passive heat exposure, older adults reported similar heat-related symptoms and lower mood disturbance than young adults. Furthermore, self-reported symptoms and mood disturbance were lower in older adults with common age-associated health conditions than young adults and healthy age-matched counterparts. Perceptual responses to heat in older adults can underestimate their level of thermal strain compared with young adults, which may contribute to their increased heat vulnerability.

Cause-specific accidental deaths and burdens related to ambient heat in a warming climate: A nationwide study of China

BackgroundFuture warming is projected to increase the heat-related mortality burden, especially for vulnerable populations. However, most previous studies focused on non-accidental morbidity or mortality, with far less research on heat-related accidental events. MethodsWe collected individual accidental death records among all residents in Chinese mainland from June to August during 2013–2019. Accidental deaths were further divided into several subtypes by different causes. We used an individual-level, time-stratified, case-crossover study design to estimate the association between daily mean temperature and accidental deaths, and estimate its variation in seven geo-climatic zones, age (5–64, 65–74, ≥75), and sex (male, female). We then estimated the temperature-related excess accidental deaths under global warming scenarios of 1.5, 2, and 3℃. FindingsA total of 711,929 accidental death records were included in our study. We found that higher temperatures were associated with increased risks of deaths from the total accidental events and four main subtypes, including traffic, falls, drowning, and unintentional injuries. We also found that younger individuals (ages 5–64) and males faced a higher risk of heat-related mortality due to total accidents, traffic incidents, and drowning. For future climate scenarios, even under the 1.5℃ climate change scenario, 6,939 (95% eCI (empirical Confidence Interval): 6,818–7,067) excess accidental deaths per year are attributed to higher summertime daily temperature over mainland China, and the number of accidental deaths would increase by 16.71% and 33.59% under the 2℃ and 3℃ climate change scenarios, respectively. For residents living in southern coastal and northwest inland regions, the projected increase in accidental death is higher. ConclusionsThis nationwide study confirms that higher summer temperatures are linked to an increased risk of accidental deaths. Younger age groups and males face a higher risk. This indicates that current estimates of the health effects of climate change might be underestimated, particularly for younger populations.

Rapid increase in the risk of heat-related mortality

Heat-related mortality has been identified as one of the key climate extremes posing a risk to human health. Current research focuses largely on how heat mortality increases with mean global temperature rise, but it is unclear how much climate change will increase the frequency and severity of extreme summer seasons with high impact on human health. In this probabilistic analysis, we combined empirical heat-mortality relationships for 748 locations from 47 countries with climate model large ensemble data to identify probable past and future highly impactful summer seasons. Across most locations, heat mortality counts of a 1-in-100 year season in the climate of 2000 would be expected once every ten to twenty years in the climate of 2020. These return periods are projected to further shorten under warming levels of 1.5 °C and 2 °C, where heat-mortality extremes of the past climate will eventually become commonplace if no adaptation occurs. Our findings highlight the urgent need for strong mitigation and adaptation to reduce impacts on human lives.

Age alters the thermoregulatory responses to extreme heat exposure with accompanying activities of daily living.

Older adults are at greater risk for heat-related morbidity and mortality, due in part to age-related reductions in heat dissipating capabilities. Previous studies investigating the impact of age on responses to heat stress used approaches that lack activities of daily living and therefore may not accurately depict the thermal/physiological strain that would occur during actual heatwaves. We sought to compare the responses of young (18-39 yr) and older (≥65 yr) adults exposed to two extreme heat simulations. Healthy young (n = 20) and older (n = 20) participants underwent two 3-h extreme heat exposures on different days: 1) DRY (47°C and 15% humidity) and 2) HUMID (41°C and 40% humidity). To mimic heat generation comparable with activities of daily living, participants performed 5-min bouts of light physical activity dispersed throughout the heat exposure. Measurements included core and skin temperatures, heart rate, blood pressure, local and whole body sweat rate, forearm blood flow, and perceptual responses. Δ core temperature (Young: 0.68 ± 0.27°C vs. Older: 1.37 ± 0.42°C; P < 0.001) and ending core temperature (Young: 37.81 ± 0.26°C vs. Older: 38.15 ± 0.43°C; P = 0.005) were greater in the older cohort during the DRY condition. Δ core temperature (Young: 0.58 ± 0.25°C vs. Older: 1.02 ± 0.32°C; P < 0.001), but not ending core temperature (Young: 37.67 ± 0.34°C vs. Older: 37.83 ± 0.35°C; P = 0.151), was higher in the older cohort during the HUMID condition. We demonstrated that older adults have diminished thermoregulatory responses to heat stress with accompanying activities of daily living. These findings corroborate previous reports and confirm epidemiological data showing that older adults are at a greater risk for hyperthermia.NEW & NOTEWORTHY Using an experimental model of extreme heat exposure that incorporates brief periods of light physical activity to simulate activities of daily living, the extent of thermal strain reported herein more accurately represents what would occur during actual heatwave conditions. Despite matching metabolic heat generation and environmental conditions, we show that older adults have augmented core temperature responses, likely due to age-related reductions in heat dissipating mechanisms.

Climatic and Economic Background Determine the Disparities in Urbanites' Expressed Happiness during the Summer Heat.

Climate-change-induced extreme weather events increase heat-related mortality and health risks for urbanites, which may also affect urbanites' expressed happiness (EH) and well-being. However, the links among EH, climate, and socioeconomic factors remain unclear. Here we collected ∼6 million geotagged tweets from 44 Chinese prefecture-level cities based on Sina Weibo and performed a quadratic regression model to explore the relationships between summer heat and EH. A three-stage analysis was developed to examine spatiotemporal heterogeneity and identify factors contributing to disparities in urbanites' EH. Results show that all cities exhibited a similar hump-shaped relationship, with an overall optimal temperature (OT) of 22.8 °C. The estimated OT varied geographically, with 25.3, 23.8, and 20.0 °C from north to south. Moreover, a 1 standard deviation increase in heatwave intensity was associated with a 0.813 (95% CI: 0.177, 1.449) standard deviation decrease in EH. Notably, within the geographic scope of this study, it was observed that urbanites in northern China and economically underdeveloped cities faced significantly lower heat risks during the summer heat. This research provides insight for future studies and practical applications concerning extreme weather events, urbanites' mental health, and sustainable urban development goal.

Physiological responses to 9 hours of heat exposure in young and older adults. Part I: Body temperature and hemodynamic regulation.

Aging is associated with an elevated risk of heat-related mortality and morbidity, attributed, in part, to declines in thermoregulation. However, comparisons between young and older adults have been limited to brief exposures (1-4 h), which may not adequately reflect the duration or severity of the heat stress experienced during heat waves. We therefore evaluated physiological responses in 20 young (19-31 yr; 10 females) and 39 older (61-78 yr; 11 females) adults during 9 h of rest at 40°C and 9% relative humidity. Whole body heat exchange and storage were measured with direct calorimetry during the first 3 h and final 3 h. Core temperature (rectal) was monitored continuously. The older adults stored 88 kJ [95% confidence interval (CI): 29, 147] more heat over the first 3 h of exposure (P = 0.006). Although no between-group differences were observed after 3 h [young: 37.6°C (SD 0.2°C) vs. older: 37.7°C (0.3°C); P = 0.216], core temperature was elevated by 0.3°C [0.1, 0.4] (adjusted for baseline) in the older group at hour 6 [37.6°C (0.2°C) vs. 37.9°C (0.2°C); P < 0.001] and by 0.2°C [0.0, 0.3] at hour 9 [37.7°C (0.3°C) vs. 37.8°C (0.3°C)], although the latter comparison was not significant after multiplicity correction (P = 0.061). Our findings indicate that older adults sustain greater increases in heat storage and core temperature during daylong exposure to hot dry conditions compared with their younger counterparts. This study represents an important step in the use of ecologically relevant, prolonged exposures for translational research aimed at quantifying the physiological and health impacts of hot weather and heat waves on heat-vulnerable populations.NEW & NOTEWORTHY We found greater increases in body heat storage and core temperature in older adults than in their younger counterparts during 9 h of resting exposure to hot dry conditions. Furthermore, the age-related increase in core temperature was exacerbated in older adults with common heat-vulnerability-linked health conditions (type 2 diabetes and hypertension). Impairments in thermoregulatory function likely contribute to the increased risk of heat-related illness and injury seen in older adults during hot weather and heat waves.