Physiological factors characterizing heat-vulnerable older adults: A narrative review

Ambient temperature and wet bulb globe temperature outperform heat index in predicting hydration status and heat perception in a semi-arid environment

BACKGROUND

Climate change is increasing temperatures, frequency of heatwaves, and erratic rainfall, which threatens human biology and health, particularly in already extreme environments. Therefore, it is important to understand how environmental heat stress measures are tied to human water needs and thermoregulation under increasingly hot conditions.

AIM

To test how ambient temperature, heat index, and wet bulb globe temperature (WBGT) relate to hydration status and thermal heat perception in a hot, semi-arid environment.

SUBJECTS AND METHODS

Urine samples, perceived heat stress, and anthropometrics were collected among Daasanach semi-nomadic pastoralists (n = 187 children, n = 231 adults) in northern Kenya. Environmental heat stress measures were recorded at sample collection; samples' urine specific gravity (USG) was measured.

RESULTS

Multiple linear and logistic regressions indicate that all environmental heat stress measures were associated with USG, odds of dehydration, and heat perception. Ambient temperature performed marginally better than WBGT, and both performed better than heat index. These associations were stronger among children than adults.

CONCLUSION

In a hot, semi-arid climate, ambient temperature and WBGT accurately predict human water needs and heat stress, with children more vulnerable to dehydration. To mitigate consequences of extreme heat, local bioculturally-appropriate hydration (e.g. tea) and cooling (e.g. shade) strategies should be encouraged.

Low and high air temperature and cardiovascular risk

Temperature extremes are one facet of global warming caused by climate change. They have a broad impact on population health globally. Due to specific individual- and area-level factors, some subgroups of the population are at particular risk. Observational data has demonstrated that the association between temperature and mortality and cardiovascular mortality is U- or J-shaped. This means that beyond an optimal temperature, both low and high temperatures increase cardiovascular risk. In addition, there is emerging epidemiological data showing that climate change-related temperature fluctuations may be particularly challenging for cardiovascular health. Biological plausibility for these observations comes from the effect of cold, heat, and temperature fluctuations on risk factors for cardiovascular disease. Shared mechanisms of heat and cold adaptation include sympathetic activation, changes in vascular tone, increased cardiac strain, and inflammatory and prothrombotic stimuli. The confluence of these mechanisms can result in demand ischemia and/or atherosclerotic plaque rupture. In conclusion, public health and individual-level measures should be taken to protect susceptible populations, such as patients with risk factors and/or pre-existing cardiovascular disease, from the adverse effects of non-optimal temperatures. This review aims to provide an overview of the association between temperature extremes and cardiovascular disease through the lens of pathophysiology and observational data. It also highlights some specific meteorological aspects, gives insight to the interplay of air temperature and air pollution, touches upon social dimensions of climate change, and tries to give a brief outlook into what to expect from the future.

Knowledge, Awareness, Practices, and Perceptions of Risk and Responsibility Related to Extreme Heat:: An Exploratory Survey of Older Adults in Canada

OBJECTIVES

Knowledge and risk perception are driving factors for initiating appropriate health-protective actions during extreme heat events (EHEs). We sought to examine the (1) current knowledge of heat as a health threat, (2) perception of personal vulnerability to heat, (3) role of heat warnings and heat alert and response systems in initiating heat mitigating practices, and (4) opinions of community preparedness among heat-vulnerable older adults, as well as explore factors that may influence these concepts.

DESIGN

Cross-sectional survey.

SETTING

Canada.

PARTICIPANTS

Individuals aged 50 years or older.

MAIN OUTCOME MEASURES

The number of respondents and percentage of the total sample were calculated based on individual response rates to each question. To explore factors that may have influenced the respondents' understanding of heat health knowledge, awareness, and risk perception, a bootstrapped least absolute shrinkage and selection operator regression was conducted.

RESULTS

1027 respondents (69% female, median age: 68 years) from 10 provinces/territories. Most felt knowledgeable about heat stress (74%), but many indicated that greater effort is needed to increase public awareness of EHE (64%). Self-reported responsiveness to heat alerts was also high (88%) despite many respondents reporting a low level of self-perceived risk (66%) and characteristics of heat susceptibility (eg, age, comorbidities).

CONCLUSIONS

In our sample of older Canadians, various factors influenced knowledge, perceived heat vulnerability, responsiveness to heat alerts, and perception of community preparedness. These findings can help inform public heat preparedness initiatives to ensure they align with the needs of older Canadians.

The Impact of Power Outages on Cardiovascular Hospitalizations Among Medicare Fee-for-service Enrollees in New York State, 2017-2018

BACKGROUND

Power outages are common. They can result in exposure to extreme temperatures by shutting off temperature-controlling devices, and thereby also cause stress. Consequently, outages may precipitate cardiovascular disease (CVD)-related hospitalizations. We assessed this relationship among older adults.

METHODS

We leveraged 2017-2018 data from 245,452 New York State Medicare Fee-for-Service beneficiaries (65+ years) with 390,530 CVD hospitalizations. Using NY Department of Public Services data, we calculated total hours without power 1 day, 1-2 days, and 1-3 days before case and control periods, with an outage ZIP Code Tabulation Area (ZCTA)-hour defined based on ≥10% of customers in a ZCTA-hour without power in primary analyses. We used a case-crossover study design and ran conditional logistic regression to assess associations separately within each urbanicity level: New York City (NYC), non-NYC urban, and rural areas. We additionally stratified models by warm versus cool season, individual-level age and sex, and ZCTA-level socioeconomic factors. Secondarily, we considered emergency (n = 298,910) and nonemergency hospitalizations separately.

RESULTS

We generally observed null associations between power outages and all CVD hospitalizations across New York State and within subgroups. For example, in NYC, we observed a rate ratio of 1.05 (95% confidence interval: 0.85, 1.30) for each additional power outage hour 1 day prior.

CONCLUSIONS

The case-crossover design we used eliminated time-fixed confounding, but there were a limited number of exposed cases, limiting statistical power. Future studies should investigate co-occurring severe weather, span additional years, and evaluate other and broader geographic areas.

The association between outdoor ambient temperature and depression and mania: An ecological momentary assessment study

BACKGROUND

Environmental heat exposure can negatively impact mental health. Evidence for its effect on mood disorder symptoms is inconsistent. Current studies are limited by poor temporal and geographical resolution.

METHODS

We used ecological momentary assessment (EMA) data from the smartphone app juli to investigate the association between real-time mean and maximum ambient temperature collected from smartphone geolocation, and depressive and manic symptom scales, every two weeks, in adults with depression and bipolar disorder. We used negative binomial mixed-effects regression models, controlled for demographic and weather variables, and stratified by season.

RESULTS

We analysed data from 4000 participants with depressive symptom scores and 2132 with manic symptom scores, between 2021 and 2023. We found that each 1 °C increase in mean daily temperature in the preceding two weeks was associated with a 0.2 % reduction in depressive symptom scores (coeff 0.998, 95%CI 0.997-0.999) and a 0.4 % increase in manic symptom scores (coeff 1.004, 95%CI 1.001-1.007). Associations between maximum temperature and symptom scores followed a similar pattern. These findings were context dependent, based on season and individual's normal heat exposure.

LIMITATIONS

We were unable to capture several socio-demographic covariates, had limited geographical information due to privacy regulations, and included a non-random sample.

CONCLUSIONS

We found evidence that higher temperatures were associated with increased manic symptoms and decreased depressive symptoms, indicating an important relationship between temperature and the mood disorder continuum. With global heating, there is a need to understand the impact of temperature on mood symptoms, to provide targeted clinical prevention and support. This study demonstrates potential for EMA methods to inform our understanding of these links.

Associations of wildfire-derived particulate matter with hospitalization, emergency department visits and mortality: A systematic review and meta-analysis

Epidemiological studies on wildfire smoke exposure and its associated disease morbidities and mortalities are rapidly accumulating in recent years. However, the findings of the existing studies have not been quantitatively evaluated with a conclusion. We conducted a systematic review and meta-analysis for the studies focused on associations of wildfire-sourced particles (PM2.5 and PM10) with cardiorespiratory diseases and mortality. We reviewed all literatures related to wildfire particles (PM2.5 and PM10) and cardiorespiratory disease morbidities [hospital admission, emergency department (ED) visits] and mortality (all-cause and cause-specific) from January 1, 2000 to August 1, 2024. Meta-analyses were conducted to summarize Relative Risks (RRs) and 95% confidence intervals (CIs) across studies when at least three studies were available for a particular exposure-outcome. All articles were assessed for risk of bias using a standard tool (Grading of Recommendations Assessment, Development and Evaluation, GRADE) for quality assurance. Studies (N = 45) were increasingly published between the years of 2020-2024 and from North America (N = 21) and Australia (N = 11) where wildfires are common. In the meta-analysis of over 124 million patients, wildfire smoke was consistently associated with increased risk of all-cause mortality (RR: 1.02, 95% CI 1.01-1.03 for PM2.5 per 10 μg/m3) and respiratory outcomes, including hospital admission (1.04, 95% CI 1.02-1.05 for wildfire PM2.5 and 1.01, 95% CI 1.00-1.02 for wildfire PM10) and ED visits (1.04, 95% CI 1.02-1.06 for wildfire PM2.5). Associations between wildfire PM2.5 and cardiovascular diseases were inconclusive (mortality: 1.02, 95% CI 1.01-1.03; hospital admission: 1.01, 95% CI 1.00-1.02; ED visit: 1.01, 95%CI: 0.98-1.04). Current studies provide evidence of an increased risk of hospitalization and ED visits for respiratory diseases and all-cause mortality due to wildfire PM2.5 and PM10 exposures worldwide. Future research is needed to explore health effects of wildfire exposure on cardiovascular diseases.

Billions of people exposed to increasing heat but decreasing greenness from 2000 to 2022

Rising heat stress due to climate warming poses a significant threat to human health, and greenness offers a nature-based solution to mitigate heat-related health impacts and enhance resilience. Although global greenness has increased, it remains unclear whether these trends align with the population's heat mitigation needs. In this study, we integrated spatially resolved demographic data with satellite-derived greenness metric and reanalysis-based heat stress data to construct a global profile of joint exposure at 1 × 1 km resolution from 2000 to 2022. We found that 69.3% of global populated areas and 41.3% of the global population (∼2.9 billion people) were exposed to increasing heat stress but decreasing greenness (IHDG), representing the most concerning situation for heat mitigation. Urban populations were disproportionately affected, with 50.8% exposed compared to 27.1% in rural areas. Low- and middle-income countries exhibited more pronounced trends of increasing heat stress and bore the greatest burden from IHDG, accounting for 85% of total exposed populations. Moreover, there was a notable demographic shift in IHDG-exposed populations toward older groups, exacerbating the heat mitigation crisis. This study advances the understanding of the joint dynamics of heat stress and greenness and provides a profile of population exposure at a fine grid level. By highlighting the scale of IHDG conditions, our findings emphasize the urgent need to address this environmental challenge and a significant opportunity for improving greenness to mitigate increasing heat globally. The spatially detailed assessment maps offer essential data for informed decision-making.

Validating new limits for human thermoregulation

Recent projections suggest that large geographical areas will soon experience heat and humidity exceeding limits for human thermoregulation. The survivability limits modeled in that research were based on laboratory studies suggesting that humans cannot effectively thermoregulate in wet bulb temperatures (Twb) above 26 to 31 °C, values considerably lower than the widely publicized theoretical threshold of 35 °C. The newly proposed empirical limits were derived from the Twb corresponding to the core temperature inflection point in participants exposed to stepped increases in air temperature or relative humidity in a climate-controlled chamber. Despite the increasing use of these thermal-step protocols, their validity has not been established. We used a humidity-step protocol to estimate the Twb threshold for core temperature inflection in 12 volunteers. To determine whether this threshold truly demarcates the Twb above which thermoregulation is impossible, each participant was subsequently exposed to Twb above (~33.7 °C, Tabove) and below (~30.9 °C, Tbelow) their respective inflection point (~32.3 °C, Twb) for up to 9 h (in random order). Core temperature rose continuously in Tabove. It was projected that core temperatures associated with heat stroke (40.2 °C) would occur within 10 h. While Tbelow was also uncompensable, the core temperature rate of rise was considerably lower than in Tabove such that it would take >24 h to reach 40.2 °C. Our study supports thermal-step protocols as an effective technique for evaluating survivability limits for heat exposure and provides a direct assessment of the limits of human thermoregulation.

Extreme Heat, Functional Disability, and Social Isolation: Risk Disparity Among Older Adults

This study examines how functional disability worsens among older adults exposed to extreme heat, particularly those socially isolated. Analyzing data from over 35,000 older adults aged 50 or older from the Health and Retirement Study from 1996-2018, this study found that more frequent exposure to extreme heat is associated with an increase in the number of instrumental activities of daily living (IADL) that older adults find difficulty in performing over time. This heat-related disability progression is greater among those living alone and not working. However, findings indicate that maintaining contact with children and receiving higher levels of support from friends can alleviate the risk of IADL disability progression amidst extreme heat days for older adults with limited social relationships at home and work. By examining various aspects of social isolation and their nuanced effects, this study underscores the need for social support and assistance for older adults during extreme heat.

Understanding local thermal comfort and physiological responses in older people under uniform thermal environments

The ageing population has increased the attention on care services for older people, particularly concerning their health and thermal comfort. However, most existing studies focus on the overall thermal comfort of older people, with insufficient research into their local thermal needs for different body parts, impeding precise thermal adjustments and optimal thermal satisfaction. This study investigated the local thermal comfort and skin temperature of older people under various environmental conditions. The results reveal significant variations in local thermal perceptions across body parts in older people under non-neutral thermal conditions. When wearing standard clothing (long-sleeved shirt and trousers) in cool environments, the back was the coldest part, followed by the lower body. In warm environments, the back, head, and chest exhibited higher thermal sensations. Weighting factors quantifying the influence of local thermal sensations on overall thermal sensation were calculated, identifying the head and back as key regions in warm conditions, and the back, arms, and legs in cool conditions. Local skin temperature also varied significantly across the body, with the head and trunk exhibiting higher temperatures and showing less fluctuation in response to environmental changes compared to the limbs. Furthermore, regression models between local thermal sensation and skin temperature were developed. Compared to the results from young people, older subjects showed significantly smaller variations in local thermal sensations across the body, along with significantly differences in local skin temperatures. These findings highlight the importance of considering the local thermal needs and preferences in older people when designing age-friendly indoor thermal environments.

Small-area association of hourly ambient temperature and acute morbidity

Previous studies have reported the association between daily temperature and morbidity at city level, but small-area association of hourly temperature and acute morbidity is limited. We aimed to assess the association between hourly temperature and acute morbidity at the smallest administrative units (communities), and to explore the sources of regional heterogeneity. This case time series design was conducted using 145,678 non-accidental ambulance dispatch records in 328 communities in Fuzhou, China (2019-2024). Small-area associations between hourly temperatures and ambulance dispatches were assessed by quasi-Poisson regression with distributed lag nonlinear model. Multivariate meta-regressions used to explore modification of natural and social features. Unstandardized and standardized attributable number calculated for disease burden. We observed a U-shaped exposure-response curves of hourly temperature and risk of ambulance dispatches, with significantly adverse cold and heat effects referent at minimum risk temperature of 21 °C. The male and the elderly were more susceptible to non-optimal temperature. The unstandardized attributable numbers of non-accident ambulance dispatches due to cold and heat were 1,389 (95%eCI: 875, 1,748) and 590 (95%eCI: 319, 811), with corresponding standardized attribution number of 36 (95%eCI: 23, 46) and 15 (95%eCI: 8, 21). The standardized attributable number due to cold and heat were greater in the downtown and areas of higher proportions of the elderly and the higher population density, and lower NDVI level. High greenness mitigated heat-related adverse effects and temperature-related disease burden. The finding support the optimization of urbanized environment and public health strategies to reduce temperature-related disease burden under global warming.

Identifying Knowledge Gaps Regarding Heat Stroke Among an Adult Sample in Pune, India: A Descriptive Analysis

INTRODUCTION

Heat stroke is a serious health concern that occurs when the body fails to regulate its temperature, often due to extreme heat exposure. Given the rising temperatures and recurring heat waves in India, understanding and preventing heat stroke is vital. The state of Maharashtra, including Pune city, is prone to extreme heat events, making it necessary to evaluate the knowledge of residents regarding this life-threatening condition. Limited studies exist in this region to assess public knowledge on heat stroke, highlighting the importance of this research. The main objective of this study is to assess the level of knowledge regarding heat stroke among adults residing in selected areas of Pune. The study aims to identify gaps in knowledge and understand the relationship between demographic factors and knowledge levels. This information can support public health initiatives aimed at heat stroke prevention.

MATERIAL AND METHODS

A non-experimental, descriptive design was employed using a quantitative research approach. The study was conducted in selected areas of Pune. A total of 300 adult participants aged 18 and above were selected using non-probability purposive sampling. The sample size was calculated considering the finite population of the urban slums, and knowledge deficit was identified from previous literature regarding heat stroke. Data collection was carried out using a self-structured questionnaire, which included demographic variables and specific questions on knowledge of heatstroke. The content validity of the tool was established, and the test-retest method was implemented to ascertain the reliability of the tool. The pilot study was conducted to understand the feasibility of the tool on 30 samples. Frequency percentage analysis was undertaken to analyze the data collected pertaining to the knowledge regarding heatstroke.  Results: Demographic analysis showed that 80 (26.5%) participants were in the 38-47-year age group, and 162 (54%) were female. In terms of education, 162 (54%) had completed education up to the 10th grade and above. The majority of participants (101, 33.5%) had a family income of Rs. 20,001-30,000 (Indian rupees (INR)). Religion-wise analysis shows that 131 (43.5%) of participants were Hindu. Data related to knowledge revealed that 159 (53%) of participants had average knowledge regarding heat stroke, 114 (38%) had good knowledge, and 27 (9%) had poor knowledge. The study found no significant association between knowledge levels and demographic variables such as age, gender, education, family income, and religion (p > 0.05).

CONCLUSION

The findings indicate that most adults in selected areas of Pune have average knowledge of heat stroke, with only a small proportion demonstrating poor knowledge. The lack of a significant association between knowledge and demographic factors suggests that efforts to increase awareness and knowledge should be broad-based rather than targeting specific groups. Public health campaigns should aim to educate all demographic segments on the dangers of heat stroke, symptoms, and preventive measures. Given the threat posed by rising temperatures in Maharashtra, such initiatives could play a crucial role in reducing the health burden of heat-related illnesses.

Intestinal epithelial injury and inflammation after physical work in temperate and hot environments in older men with hypertension or type 2 diabetes

We tested whether older adults with well-controlled type 2 diabetes or hypertension, compared with age-matched adults without chronic disease, exhibit greater intestinal damage, microbial translocation and inflammation during exertional heat stress. Twelve healthy men (age 59 years, SD 4 years), nine with type 2 diabetes (age 60 years, SD 5 years) and nine with hypertension (age 60 years, SD 4 years) walked for 180 min at 200 W/m2 in temperate conditions (wet-bulb globe temperature 16°C) and high-heat stress conditions (wet-bulb globe temperature 32°C). Serum intestinal fatty acid binding protein (IFABP), plasma soluble cluster of differentiation 14, lipopolysaccharide-binding protein (LBP), interleukin-6 and tumour necrosis factor-alpha were measured pre- and postexercise and after 60 min recovery. Total exercise duration was lower in men with hypertension and diabetes (p ≤ 0.049), but core temperature did not differ. All markers increased more in heat versus temperate conditions (p < 0.002). In the heat, individuals with type 2 diabetes had greater postexercise increases in IFABP [+545 pg/mL (95% confidence interval: 222, 869)] and LBP [+3.64 µg/mL (1.73, 5.56)] relative to healthy control subjects (p < 0.048), but these resolved after recovery. Despite reduced exercise duration, hypertensive individuals showed similar increases in IFABP and LBP to control subjects. Our findings suggest that older workers with well-controlled type 2 diabetes or hypertension might have greater vulnerability to heat-induced gastrointestinal barrier disturbance and downstream inflammatory responses when compared with otherwise healthy, age-matched adults during prolonged exercise in the heat.

Corrigendum to 'Extreme temperature increases the risk of COPD morbimortality: A systematic review and meta-analysis [Science of The Total Environment, Vol 958 [2025] 178087'

INTRODUCTION

This systematic review examines how extreme temperatures impact Chronic Obstructive Pulmonary Disease (COPD) morbidity and mortality, focusing on identifying vulnerable subpopulations.

METHODS

We conducted a systematic literature search from January 1, 2000, to November 6, 2024, across databases like PubMed, MEDLINE and EMBASE, Web of Science, and Scopus, focusing on observational studies that quantitatively defined extreme temperatures and their impacts on COPD morbidity and mortality. Out of 3140 records, 25 studies met the inclusion criteria. We extracted data on study characteristics, effect estimates, and confounders, employing methods to assess the risk of bias and synthesize results.

RESULTS

We observed that extreme heat increased the relative risk (RR) for COPD morbimortality by 1.19-fold (95 % CI: 1.09-1.29; p < 0.05), and extreme cold increased the RR by 1.35-fold (95 % CI: 1.22-1.50; p < 0.05). Extreme heat was associated with a 1.23-fold (95 % CI: 1.11-1.35; p < 0.05) increase in COPD mortality. In contrast, extreme cold was associated with both COPD morbidity and mortality, with morbidity increasing by 1.47-fold (95 % CI: 1.26-1.71; p < 0.05) and mortality by 1.28-fold (95 % CI: 1.12-1.45; p < 0.05). Extreme heat poses a higher risk for female COPD patients compared to males. Moreover, extreme heat and cold were associated with morbimortality risk among older adults. Asian populations were sensitive to both temperature extremes, whereas Europeans were predominantly susceptible to extreme cold.

CONCLUSION

This variability in response to extreme temperatures affects COPD morbidity and mortality, emphasizing the need for tailored medical and emergency responses to effectively mitigate health risks during extreme weather events.

Meta-analysis of heat-induced changes in cardiac function from over 400 laboratory-based heat exposure studies

Heat waves are associated with increased fatalities from adverse cardiovascular events attributed to the negative effects of heat on cardiac function. However, scientific understanding of acute cardiac adjustments to heat has come primarily from laboratory experiments employing insulated and encapsulated heating modalities, most commonly water-perfused suits. We evaluated whether findings from those studies reflect cardiac responses during more natural exposures to hot ambient conditions simulated in climate-controlled chambers by synthesizing the findings from over 400 laboratory-based heat exposure studies (6858 participant-exposures) published between 1961-2024. Among all included studies, median (interquartile range) elevations in core temperature and heart rate from baseline to end-exposure were 0.9 (0.5-1.3)°C and 27 (15-40) beats/min. Multilevel mixed-effects meta-analyses revealed exacerbated elevations in heart rate, cardiac output, and rate pressure product (estimate of cardiac workload) and blunted falls in systolic pressure in participants heated via encapsulated modalities. Leveraging the large dataset, we also provide empirical estimates of body temperature and cardiovascular responses to a wide range of conditions experienced during heat waves. With rising global temperatures, ecologically-minded physiological research is needed to improve understanding of the effects of heat stress on cardiac responses and further the development of robust climate health models and evidence-based heat-health guidance.

Home Ambient Temperature and Self-Reported Attention in Community-Dwelling Older Adults

BACKGROUND

Climate change is expected to disrupt weather patterns across the world, exposing older adults to more intense and frequent periods of hot weather. Meanwhile, lab-based studies have established a causal relationship between ambient temperature and cognitive abilities, suggesting the expected rise in temperature may influence older adults' cognitive functioning. Nevertheless, it is not clear whether, and to what extent, the temperature variations in older adults' own homes-which unlike lab settings are under their control-influence their cognitive functioning. Our objective was to provide proof of concept that home ambient temperature influences self-reported ability to maintain attention in older adults.

METHODS

We conducted a longitudinal observational study, continuously monitoring the home ambient temperature and self-reported difficulty keeping attention for 12 months in 47 of community-dwelling older adults living in Boston, Massachusetts.

RESULTS

We observed a U-shaped relationship between home ambient temperature at the time of assessment and the odds ratio (OR) of reporting difficulty keeping attention such that the OR was lowest between 20°C and 24°C and doubled when moving away from this range by 4°C in either direction.

DISCUSSION

Our results suggest that even under the current climate, a considerable portion of older adults encounter indoor temperatures detrimental to their cognitive abilities. Climate change may exacerbate this problem, particularly among low-income and underserved older adults. Addressing this issue in public health and housing policy is essential to building climate resiliency in this vulnerable population.

Brain-derived neurotrophic factor in older adults exposed to simulated indoor overheating

PURPOSE

Brain-derived neurotrophic factor (BDNF) is a neuroprotective growth factor that increases in young adults during short, intense bouts of passive heat stress. However, this may not reflect the response in heat-vulnerable populations exposed to air temperatures more consistent with indoor overheating during hot weather and heatwaves, especially as the BDNF response to acute stressors may diminish with increasing age. We therefore evaluated the ambient and body temperature-dependent responses of BDNF in older adults during daylong passive heating.

METHODS

Sixteen older adults (6 females; aged 66-78 years) completed 8-h exposure to four randomized ambient conditions simulating those experienced indoors during hot weather and heatwaves in continental climates: 22 °C (air-conditioning; control), 26 °C (health-agency-recommended indoor temperature limit), 31 °C, and 36 °C (non-airconditioned home); all 45% relative humidity. To further investigate upstream mechanisms of BDNF regulation during thermal strain, we also explored associations between BDNF and circulating heat shock protein 70 (HSP70; taken as an indicator of the heat shock response).

RESULTS

Circulating BDNF was elevated by ~ 28% (1139 [95%CI: 166, 2112] pg/mL) at end-exposure in the 36 °C compared to the 22 °C control condition (P = 0.026; 26 °C-and 31 °C-22 °C differences: P ≥ 0.090), increasing 90 [22, 158] pg/mL per 1 °C rise in ambient temperature (linear trend: P = 0.011). BDNF was also positively correlated with mean body temperatures (P = 0.013), which increased 0.12 [0.10, 0.13]°C per 1 °C rise in ambient temperature (P < 0.001). By contrast, serum HSP70 did not change across conditions (P ≥ 0.156), nor was it associated with BDNF (P = 0.376).

CONCLUSION

Our findings demonstrate a progressive increase in circulating BDNF during indoor overheating in older adults.

The effect of an exercise- and passive-induced heat stress on autophagy in young and older males

Although activation of autophagy is vital for cellular survival during exposure to ambient heat and exercise, it remains unclear if autophagic activity differs between these heat stress conditions and if aging mediates this response. Young [n = 10, mean (SD): 22 (2) yr] and older males [n = 10, 70 (5) yr] performed 30 min of semi-recumbent cycling (70% maximal oxygen uptake). On a separate day, participants were immersed in warm water for 30 min, with the water temperature adjusted to induce the same increase in core temperature (rectal) as the prior exercise bout. Proteins associated with autophagy, inflammation, apoptosis, and the heat shock response (HSR) were assessed in peripheral blood mononuclear cells via Western blot before and after each exposure and during a 6-h seated recovery in a temperate environment (∼22°C). No differences in core temperature occurred at end-exposure to exercise or passive heating in either group (both, P ≥ 0.999). Older adults exhibited greater autophagic regulation (significant LC3-II accumulation) to exercise when compared with passive heating at all time points (all, P ≤ 0.022). However, passive heating alone may have impaired autophagy (elevated p62; P = 0.044). Pro-inflammatory IL-6 was elevated during both conditions (P < 0.001) in older adults. Conversely, greater autophagic initiation (i.e., beclin-2) occurred in young adults at end-exercise and 3-h recovery when compared with passive heating (both, P ≤ 0.024). The HSR and apoptotic responses were similar between conditions in both groups. Although brief exercise stimulates autophagy, exposure to ambient heat stress of an equivalent heat load may underlie autophagic dysregulation in older adults.NEW & NOTEWORTHY We show that a short-duration (30-min) bout of vigorous-intensity exercise stimulates autophagy in young and older males when performed in a temperate environment. However, when exposed to an equivalent heat load as achieved during the prior exercise bout to elicit the same relative increase in core temperature via warm-water immersion, autophagic dysregulation occurs in older but not younger males.

Impact of Heat on Respiratory Hospitalizations among Older Adults in 120 Large U.S. Urban Areas

Rationale: Extreme heat exposure is a well-known cause of mortality among older adults. However, the impacts of exposure on respiratory morbidity across U.S. cities and population subgroups are not well understood. Objectives: A nationwide study was conducted to determine the impact of high heat on respiratory disease hospitalizations among older adults (≥65 yr of age) living in the 120 largest U.S. cities between 2000 and 2017. Methods: Daily rates of inpatient respiratory hospitalizations were examined with respect to variations in ZIP code-level daily mean temperature or heat index. For each city, we estimated cumulative associations (lag days 0-6) between warm-season heat (June to September) and cause-specific respiratory hospitalizations using time-stratified conditional quasi-Poisson regression with distributed lag nonlinear models. We estimated nationwide associations using multivariate meta-regression and updated city-specific associations via best linear unbiased prediction. With stratified models, we explored effect modification by age, sex, and race (Black or White). Results are reported as percentage change in hospitalizations at high temperatures (95th percentile) compared with median temperatures for each outcome, demographic group, and metropolitan area. Results: We identified 3,275,033 respiratory hospitalizations among Medicare beneficiaries across 120 large U.S. cites between 2000 and 2017. Nationwide, 7-day cumulative associations at high temperatures resulted in a 1.2% (95% confidence interval, 0.4-2.0%) increase in hospitalizations for primary diagnoses of all-cause respiratory disease, driven primarily by increases in respiratory tract infections (1.8% [95% confidence interval, 0.6-3.0%]) and chronic respiratory diseases and/or respiratory failure (1.2% [95% confidence interval, 0.0-2.4%]). Stronger associations were observed when exposure was defined using the heat index instead of mean temperature. Across the 120 cities, we observed considerable geographic variation in the relative risk of heat-related respiratory hospitalizations, and we observed disproportionate burdens of heat-related respiratory hospitalizations among the oldest beneficiaries (≥85 yr of age) and among Black beneficiaries living in South Atlantic cities. During the 18-year study period, there were an estimated 11,710 excess respiratory hospitalizations due to heat exposure. Conclusions: Results suggest that high temperature and humidity contribute to exacerbation of respiratory tract infections and chronic lung diseases among older adults. Geographic variation in heat-related hospitalization rates suggests that contextual factors largely account for disproportionate burdens, and area-level influences should be further investigated in multicity studies.

The impact of temperature changes on the health vulnerability of migrant workers: an empirical study based on the China family panel studies

Introduction

Migrant workers constitute a significant portion of China's workforce, and their health directly affects labor supply and economic stability. Health vulnerability plays a crucial role in shaping the well-being of migrant workers, yet its determinants, particularly the impact of temperature change, remain underexplored. This study, based on the socio-ecological model, investigates how temperature variations influence the health vulnerability of migrant workers in China.

Methods

Using data from 2020, this study quantifies health vulnerability and examines the impact of temperature fluctuations across different seasons. Robustness checks, including dependent variable substitutions and model modifications, ensure the reliability of the findings. Furthermore, a mechanism analysis is conducted to explore the underlying pathways through which temperature change affects health vulnerability.

Results

The findings reveal that rising temperatures in spring, summer, and winter significantly exacerbate the health vulnerability of migrant workers, while increasing autumn temperatures mitigate it. Mechanism analysis identifies heightened psychological burden as a key channel through which temperature change worsens health vulnerability. Additionally, generational differences emerge: older migrant workers are more adversely affected by elevated spring temperatures, whereas younger workers exhibit greater sensitivity to rising summer temperatures.

Discussion

These results underscore the necessity of targeted health interventions and adaptive labor protection policies. By highlighting the seasonal and generational disparities in the effects of temperature change, this study offers theoretical and empirical support for enhancing the resilience of migrant workers to climate variations. The findings provide valuable insights for policymakers in designing strategies to safeguard the health and stability of the migrant workforce.

A digital heat early warning system for older adults

Extreme heat events lead to considerable health burden and are becoming more severe and frequent, calling for the development of effective population-based and individualised heat early warning systems. We developed an individualised heat early warning system and tested it in 78 older adults' ( ≥ 65 years) homes in Southeast Queensland, Australia. Quantitative and qualitative data from this proof-of-concept testing study showed that the Ethos system performed well on a standard usability scale (mean score of 78 on the System Usability Scale). Following a summer-time use of this early warning system, there were increases in heat preparedness (P < 0.001, marginal homogeneity tests) but no significant increases in heat health risk perception or the uptake of low-cost cooling measures (e.g., hand/forearm bath, fans). This proof-of-concept research demonstrated the usability of this tailored, actionable, real-time digital heat early warning system, although the effectiveness of the system remains to be evaluated in a robust trial design.

Mapping climate change interaction with human health through DPSIR framework: Qatar perspective

This study investigates the interactions between climate change and human health with a particular focus on Qatar, using the DPSIR (Driving Forces, Pressures, States, Impacts, Responses) framework. Key drivers, including economic development and population growth, contribute to increased greenhouse gas (GHG) emissions, exerting pressure on Qatar's climate through rising temperatures and altered precipitation patterns, as modeled by the MIT Regional Climate Model (MRCM). The findings reveal critical gaps in understanding the state of climate-health interactions, including insufficient disease data, incomplete climate-health linkages, and significant research gaps. These limitations hinder targeted responses to climate-sensitive diseases, which have shown an increase over the years. The study identifies the pathways through which climatic shifts contribute to immediate health risks, such as heat-related illnesses and respiratory conditions, as well as long-term impacts, including chronic diseases and mental health challenges. Despite Qatar's efforts through national and international strategies, the DPSIR analysis highlights the urgent need for enhanced research, improved data collection, and tailored actions to address these challenges. Strengthened adaptation, resilience-building, and emission reduction strategies remain essential for safeguarding public health in the face of accelerating climate change.

Biophysical versus machine learning models for predicting rectal and skin temperatures in older adults

This study compares the efficacy of machine learning models to traditional biophysical models in predicting rectal (Tre) and skin (Tsk) temperatures of older adults (≥60 years) during prolonged heat exposure. Five machine learning models were trained on data using 4-fold cross validation from 162 day-long (8-9h) sessions involving 76 older adults across six environments, from thermoneutral to heatwave conditions. These models were compared to three biophysical models: the JOS-3 model, the Gagge two-node model, and an optimised two-node model. Our findings show that machine learning models, particularly ridge regression, outperformed biophysical models in prediction accuracy. The ridge regression model achieved a Root-Mean Squared Error (RMSE) of 0.27 °C for Tre, and 0.73 °C for Tsk. Among the best biophysical models, the optimised two-node model achieved an RMSE of 0.40 °C for Tre, while JOS-3 achieved an RMSE of 0.74 °C for Tsk. Of all models, ridge regression had the highest proportion of participants with Tre RMSEs within clinically meaningful thresholds at 70% (<0.3 °C) and the highest proportion for Tsk at 88% (<1.0 °C), tied with the JOS-3 model. Our results suggest machine learning models better capture the complex thermoregulatory responses of older adults during prolonged heat exposure. The study highlights machine learning models' potential for personalised heat risk assessments and real-time predictions. Future research should expand upon training datasets, incorporate more dynamic conditions, and validate models in real-world settings. Integrating these models into home-based monitoring systems or wearable devices could enhance heat management strategies for older adults.

Analysis of clinical characteristics and risk factors for patients with heat stroke in western China in 2022: a multicenter retrospective study

Objectives

To analyzed the clinical characteristics and treatment modalities of heat stroke (HS) and to identify risk factors for a poor prognosis of HS and provide reference suggestions for its treatment and prevention.

Measurements and main results

We enrolled a total of 247 patients, with hypertension, diabetes, and psychosis being the top three comorbidities associated with HS. The incidence of HS was higher among males and older individuals. Compared to the control group, the poor prognosis group experienced higher temperatures, a higher incidence of cerebral edema, and gastrointestinal bleeding (all p < 0.05). The poor prognosis group had significantly higher blood pH, HCO3-, Lac, Scr, AST, ALT, DBIL, CKMB, PT, DD, and PLT (all p < 0.05). Furthermore, logistic regression analysis revealed that Lac, Scr, and APACHE II were risk factors for poor prognosis (p < 0.05). The AUC values for the combined diagnostic model were 0.848 (95% CI: 0.781-0.914). Male morbidity, the number of patients with combined hypertension, the prognosis, and the APACHE II score and ALT level were all greater (p < 0.05) in the CHS group. The Kaplan-Meier analysis revealed that the CHS group had a significantly higher mortality rate than the EHS group.

Conclusion

A high incidence of hypertension, diabetes, psychosis, men, and older persons may be associated with HS. HS patients with high blood cell counts, impaired coagulation, liver and kidney diseases, and those with a specific type of CHS may face a poor prognosis. In patients with heart failure, APACHE II, Lac, and Scr were independent risk factors for a poor prognosis.

Association of ambient temperature with social isolation among the community-dwelling Chinese older adults: A cross-sectional study in Hong Kong

Background

The adverse health impacts of ambient temperature have been well-documented, encompassing not only the mortality and morbidity burden but also mood and mental health disorders. However, the relationship between temperature and social isolation remains unexplored. The objective of the current study was to investigate the potential associations between ambient temperature and social isolation among the aging population.

Methods

We took advantage of a cross-sectional survey conducted between January 2017 and November 2018 from a community service program special for older adults aged ≥60 who lived in a central community of Hong Kong. The personal social isolation was assessed by the validated Lubben Social Network Scale-6 (LSNS-6), with a score ranging from 0 to 30 and score of less than 12 indicating social isolation. The environmental exposures, including ambient temperature, sunshine hours, rainfalls, and air pollution, were obtained from the nearby monitoring stations. The association of ambient temperature with LSNS-6 score or social isolation was examined by the generalized linear models while adjusting the potential confounding from other environmental exposures and personal sociodemographic factors.

Results

Among the 1616 participants, the distribution of LSNS-6 score was approximately normal and the mean score was a bit higher on cool days than on hot days (13.0 vs. 12.2). Compared with cool temperatures (14.4-19.5oC), the independent effect estimates of hot ambient temperatures (24.5-28.7oC) was associated with a 2.38 (95%CI: 1.63-3.13) decrease in LSNS-6 score. Meanwhile, we observed statistically significant associations of sunshine exposure, gender, health status, marital status, living alone, religion, and housing type with LSNS-6 score or social isolation.

Conclusions

Our study revealed a clear association between ambient cool temperatures and reduced social isolation, as well as association between hot temperatures and social isolation among older Chinese adults residing in the urban community of Hong Kong.

Passive heat therapy for cardiovascular disease: current evidence and future directions

Passive heat therapy is gaining popularity as an intervention to promote cardiovascular, physiological, and, to a lesser degree, thermoregulatory adaptations in patients with cardiovascular disease. Despite this, the efficacy of heat therapy to elicit these adaptations remains unknown. We searched five databases for original research, screening 2913 studies and identifying 18 eligible studies. Heat therapies included Waon therapy, balneotherapy, water perfused trousers, Finnish sauna, and foot immersion. Interventions were administered across various time frames (20-90 min) and performed 3-7 times per week, for durations of 2-8 weeks. The studies collectively involved a diverse population (mean age: 67 (10) years) with cardiovascular diseases. Heat therapy was consistently shown to improve ejection fraction, flow-mediated dilation, brain natriuretic peptide levels, New York Heart Association classification, and 6 min walk distance. However, positive effects on resting heart rate and blood pressure were infrequently observed, and thermoregulatory responses scarcely reported. Heat therapy may increase sweat rate during heat exposure and reduce resting core temperature, but adaptive skin blood flow responses were not observed. Passive heat therapy shows promising utility in patients with cardiovascular disease, while secondary benefits such as markers of thermoregulatory adaptation may also be observed, these require further investigation.

The combined effects of sleep and extreme heat exposure on cognitive function among older adults

BACKGROUND

Extreme heat is linked to cognitive impairment. Normal sleep duration and good sleep quality can reduce cognitive impairment risks. However, the combined impact of sleep (duration and quality) and extreme heat on cognitive impairment is unclear. This study tests whether normal sleep duration and good sleep quality during a heatwave reduce cognitive impairment compared to poor sleep quality and long sleep duration in older adults.

METHODS

This study used cohort data from 9153 older adults. Extreme heat was defined as periods ≥ 3 days with daily minimum temperatures above the 92.5th percentile during the warm season. Cognitive function was assessed with the Mini-Mental State Examination (MMSE). Sleep duration was categorized as long, normal, or short, and sleep quality as good or poor. Six and four categories were used for combinations of heatwave exposure with sleep duration and quality, respectively. Cox regression models were applied for analysis.

RESULTS

Compared to those with long sleep duration during heatwaves, participants exposed to heatwaves with normal sleep duration had lower cognitive impairment risk (HR: 0.86, 95 %CI: 0.76-0.97). Those exposed to extreme heat with short sleep duration also showed lower cognitive risks (HR: 0.74, 95 %CI: 0.62-0.88). Compared to those with poor sleep quality during heatwave, participants with good sleep quality during heatwaves did not show significantly lower cognitive impairment risk (HR: 1.10, 95 %CI: 0.98-1.23).

CONCLUSION

Older adults with normal or short sleep duration during heatwaves may face lower cognitive impairment risks, highlighting the importance of sleep guidance to protect cognitive health during extreme heat.

Effects of pedestal-mounted electric fans on self-reported symptoms and mood-state in older adults exposed to indoor overheating during a simulated heatwave: an exploratory analysis

Recent evidence from modelling and laboratory-based studies showed that electric fans are ineffective at meaningfully lowering core temperature in older adults at air temperatures of 36 °C. However, their influence on self-reported environmental symptoms and mood-state during daylong use in hot indoor environments remains unclear. Eighteen older adults (8 females, median (interquartile range); 72 (67-76 years)) completed three randomized 8 h heat exposures (36 °C, 45% relative humidity) with a fan generating air speeds of 0 (no fan, control), 2, or 4 m/s at the front of the body positioned 1 m away. Participants were seated throughout, except for 4 × 10 min periods of simulated activities of daily living (stepping (∼2.25 metabolic equivalents (METs)). Core temperature, mean skin temperature, and heart rate areas under the curve (AUCs, hours 0-8) were calculated to assess cumulative physiological strain. Total Symptom Scores (68-item Environmental Symptoms Questionnaire) as well as Total Mood Disturbance and Energy Index (40-item Profile of Mood States questionnaire) were evaluated at end-heating (adjusted for pre-exposure). Core temperature, mean skin temperatures, and heart rate AUCs were not different between conditions (all p ≥ 0.087). Total Symptom Scores were 0.89-fold [0.81, 0.97] lower with fan use (combined across speeds) compared to no fan (p = 0.009). Energy Index scores were 2.4 points [0.8, 4.0] higher with fan use compared to no fan (p = 0.004). However, mood disturbance was not significantly different between conditions (p = 0.345). Our exploratory analysis show that fans can reduce self-reported symptoms and increase perceived energy levels in older adults in overheated indoor environments, despite no meaningful attenuation of physiological strain. ClinicalTrials.gov Identifier: NCT05695079.

Extreme temperature increases the risk of COPD morbimortality: A systematic review and meta-analysis

INTRODUCTION

This systematic review examines how extreme temperatures impact chronic obstructive pulmonary disease (COPD) morbidity and mortality, focusing on identifying vulnerable subpopulations.

METHODS

We conducted a systematic literature search from January 1, 2000, to November 6, 2024, across databases like PubMed, MEDLINE and EMBASE, Web of Science, and Scopus, focusing on observational studies that quantitatively defined extreme temperatures and their impacts on COPD morbidity and mortality. Out of 3140 records, 25 studies met the inclusion criteria. We extracted data on study characteristics, effect estimates, and confounders, employing methods to assess the risk of bias and synthesize results.

RESULTS

We observed that extreme heat increased the relative risk (RR) for COPD morbimortality by 1.16-fold (95 % CI: 1.08-1.26; p < 0.05), and extreme cold increased the RR by 1.32-fold (95 % CI: 1.20-1.46;). Extreme heat was associated with a 1.19-fold (95 % CI: 1.09-1.30; p < 0.05) increase in COPD mortality. In contrast, extreme cold was associated with both COPD morbidity and mortality, with morbidity increasing by 1.47-fold (95 % CI: 1.26-1.71; p < 0.05) and mortality by 1.23-fold (95 % CI: 1.10-1.38; p < 0.05). Extreme heat poses a higher risk for female COPD patients compared to males. Moreover, extreme heat and cold were associated with morbimortality risk among older adults. Asian populations were sensitive to both temperature extremes, whereas Europeans were predominantly susceptible to extreme cold.

CONCLUSION

This variability in response to extreme temperatures affects COPD morbidity and mortality, emphasizing the need for tailored medical and emergency responses to effectively mitigate health risks during extreme weather events.

Effect of aerobic fitness on the validity of the Calera Research™ sensor to estimate core temperature during exercise

The Calera Research™ is a heat flux device advertised to estimate core temperature (Tc) during physical activity and is widely used by athletes in various sport disciplines. The device estimates Tc from skin temperature, heart rate, and heat flux, outcomes that can be affected by aerobic fitness. However, there is a relatively small body of literature exploring its validity and, specifically, how the device bias may be influenced by aerobic fitness. The objective of this study was to assess the validity of the Calera Research™ sensor compared with telemetric ingestible pills for estimating Tc and to determine whether aerobic fitness impacts accuracy. Twenty participants (10 females) performed a cycling-based ramp-incremental exercise test to volitional exhaustion in a temperature controlled environment (22 °C) during which Tc was measured directly from ingested pills (eCelsius performance system) and by the Calera device. Compared to the ingestible telemetric pills, the Calera device exhibited lower Tc values (95%CI[-0.2, -0.3 °C], p < 0.001) with an intraclass correlation of 0.47 and a bias of -0.3 ± 0.2 °C. Participants were divided into two groups (10 participants at each group) based on peak oxygen uptake (V˙ O2peak) (HL: high aerobic; LL: lower aerobic fitness). Throughout ramp-incremental exercise, HL had a lower heart rate (p < 0.001 and η2 = 0.10; 95%CI[0.1, 17.2 bits/min]) and Tc measured by the ingestible pills (p < 0.001 and η2 < 0.01, 95%CI[0.1, 0.3 °C]). However, there were no-between group differences for skin temperature and intraclass correlation values and bias were also similar. In conclusion, the estimation of Tc by Calera Research™ underestimated Tc by approximately 0.3 °C in a moderate thermal environment, but the intensity-dependent profile was similar to that of the ingestible pill method and was unaffected by aerobic fitness differences.

Effects of daylong exposure to indoor overheating on enterocyte damage and inflammatory responses in older adults: a randomized crossover trial

We evaluated enterocyte damage (IFABP), immune activation (sCD14), and inflammatory responses (TNF-α, IL-6, CRP) in 16 older adults (66-78 years) during 8 h rest in conditions simulating homes maintained at 22 °C (control), the 26 °C indoor temperature upper limit proposed by health agencies, and homes without air-conditioning during heatwaves (31 °C, 36 °C). Relative to 22 °C, IFABP was elevated ∼181 pg/mL after exposure to 31 °C (P = 0.07), and by ∼378 pg/mL (P < 0.001) after exposure to 36 °C. No differences were observed for sCD14, TNF-α, IL-6, or CRP (all P ≥ 0.26). Our data support recommendations to maintain indoor temperatures ≤ 26 °C to preserve gastrointestinal barrier integrity in heat-vulnerable persons.

Urban Heat and Burden of Hyponatremia

Importance

Hyponatremia (sodium level <135 mEq/L), the most prevalent electrolyte disorder in clinical practice, is associated with considerable clinical and economic burdens. Despite its recognized effect and indication of seasonal patterns, there is a research gap regarding heat-related hyponatremia. Addressing this issue is crucial, especially regarding projected increases in environmental temperature, particularly in urban areas.

Objective

To comprehensively analyze the association of heat in an urban setting with hyponatremia prevalence.

Design, Setting, and Participants

This cross-sectional study using retrospective time series analysis was conducted among all adult patients (age ≥18 years) presenting to the Charité-Universitätsmedizin Berlin between March 1, 2000, and August 31, 2023, with a blood sodium measurement.

Exposure

The daily heat index, which accounts for both outdoor air temperature and relative humidity.

Main Outcomes and Measures

The primary outcome measure was the daily number of hyponatremia cases, further categorized by severity. Differences in prevalence across age groups (adult patients, aged 18-65 years; and older patients, aged >65 years) and sexes were also examined.

Results

A total of 7 135 688 sodium measurements from 2 028 537 hospital visits were analyzed. The mean (SD) age at admission was 57.8 (17.8) years, and 51.7% of patients were male. A clear seasonal pattern of heat-related hyponatremia was evident among older patients, especially for moderate (sodium level, 125-129 mEq/L) and severe hyponatremia (sodium level, <125 mEq/L), where the cumulative risk over a lag period of 5 days reached a maximum relative risk (RR) of 1.26 (95% CI, 1.07-1.48) when the heat index reached 30 °C, compared with the temperature at which hyponatremia occurred least frequently. Older women were disproportionately more likely to experience hyponatremia compared with older men, with a cumulative RR of 1.10 (95% CI, 1.03-1.18) at a heat index of 26 °C. The highest RR was on lag day 0 for all subgroups (older patients: RR, 1.04 [95% CI, 1.00-1.08]; moderate and severe hyponatremia in older patients: RR, 1.05 [1.01-1.10]; and older women: RR, 1.07 [95% CI, 1.01-1.12]) and significantly increased when the heat index exceeded 15 °C (RR, 1.01 [95% CI, 1.00-1.02]).

Conclusions and Relevance

This cross-sectional study of patients with sodium measurements suggests that older people, especially women, were vulnerable to heat-related hyponatremia. Environmental heat was associated with an immediate exacerbation of hyponatremia. This finding highlights the importance of implementing prevention strategies to mitigate heat-related hyponatremia, as an increased burden in the future due to climate change is likely.

The effect of foot immersion and neck cooling on cardiac autonomic function in older adults exposed to indoor overheating: a randomized crossover trial

Foot immersion and neck cooling are recommended cooling strategies for protecting heat-vulnerable persons during heat waves. While we recently showed that these strategies do not limit core temperature increases in older adults during prolonged heat exposure, we did observe small reductions in heart rate. Expanding on these findings, we examined the effects of foot immersion with and without neck cooling on cardiac autonomic function. Seventeen adults (9 females; 65-81 years) underwent 3 randomized, 6 h exposures to 38 °C and 35% relative humidity with: no cooling (control), foot immersion (20 °C water), or foot immersion with a wet towel (20 °C) around the neck. Cardiac autonomic responses were measured at baseline and end-exposure. These included heart rate variability, cardiac and systolic blood pressure responses to standing, indexed via the 30:15 ratio and supine-to-standing systolic pressure change, respectively, and baroreflex sensitivity during repeated sit-to-stand maneuvers. The 30:15 ratio was 0.04 [95% CI: 0.01, 0.07] greater with foot immersion and neck cooling (1.08 (SD: 0.04)) relative to control (1.04 (0.06); P = 0.018). Similarly, standing systolic blood pressure was elevated 9 [0, 17] mmHg with foot immersion and neck cooling (P = 0.043). That said, neither difference remained statistically significant after adjusting for multiplicity (Padjusted ≥ 0.054). No differences in 30:15 ratio or standing systolic blood pressure were observed with foot immersion alone, while heart rate variability and baroreflex sensitivity were unaffected by either cooling intervention. While foot immersion with neck cooling potentially improved cardiac autonomic responses in older adults exposed to simulated indoor overheating, these effects were small and of questionable clinical importance.

An exploratory investigation of heart rate and heart rate variability responses to daylong heat exposure in young and older adults

Heart rate variability (HRV) has shown potential as a tool for monitoring thermal strain, but there is limited data to support its efficacy in older adults during prolonged heat exposures. We compared HRV between young (19-31 years, n = 20) and older (61-78 years, n = 39) adults during 9 h of heat exposure (40 °C, 9% RH). We also explored whether heart rate (HR) and/or HRV could be used to distinguish older adults who achieved elevated thermal strain, defined as either (1) an increase in core temperature >1.0 °C (occurring in 39%, 15/39) or (2) a reduction in systolic blood pressure >10 mm Hg (occurring in 67%, 26/39). Percentage of age-predicted maximal HR and percentage of heart rate reserve (HRR) were higher, whereas standard deviation of normal RR intervals, the square root of the mean of squared differences between successive RR intervals (RMSSD), high frequency power (HF), and cardiac vagal index (CVI) were lower in older compared to young adults during heat exposure (P ≤ 0.004). In older adults, increases in core temperature were correlated with percentage of age-predicted maximal HR, percentage of HRR, RMSSD, and CVI (P ≤ 0.031), whereas changes in systolic blood pressure were not significantly associated with HR or HRV indices (P ≥ 0.327). Receiver operating characteristic curve analysis indicated that HR and HRV indices had generally poor ability to identify older adults with elevated thermal strain (area under the curve ≤0.65). Age-related differences in HRV, consistent with vagal withdrawal among older adults, remained during daylong heat exposure, but marked heterogeneity of response likely contributed to HRV providing limited discriminatory value in identifying changes in core temperature or blood pressure in older adults.

Effect of cold beverages on whole-body heat exchange in young and older males during intermittent exercise in the heat

BACKGROUND

To mitigate health risks associated with occupational heat stress, workers are advised to adhere to a work-rest regimen, and hydrate regularly. However, it remains unclear if beverage temperature influences whole-body heat exchange during work-rest cycles, and if responses differ in older workers who have a blunted heat loss capacity.

METHODS

Ten young (mean [SD]: 22 [3] years) and 10 older (60 [4] years) males performed four 15-min bouts of moderate-intensity cycling at a fixed rate of metabolic heat production (200 W·m-2), each interspersed by 15-min rest in dry heat (40°C, ~12% relative humidity). On separate days, participants consumed either ice-slurry (~0°C), standardized to provide a heat transfer capacity of 75 kJ·m-2, or an identical mass of warm fluid (37.5°C) before the first and third exercise bouts. Evaporative and dry heat exchange (direct calorimetry) and metabolic heat production (indirect calorimetry) were measured continuously to determine cumulative heat storage (summation of heat loss and heat gain) over the entire protocol. Rectal temperature was also measured continuously.

RESULTS

Relative to warm fluid, ice-slurry ingestion reduced cumulative heat storage in young (69 [181] vs. 216 [94] kJ) and older males (90 [104] vs. 254 [140] kJ, main effect: p < 0.01), but was unaffected by age (p = 0.49). However, rectal temperature was unaffected by beverage temperature in both groups (all p ≥ 0.15).

CONCLUSION

We show that cold fluid ingestion is an appropriate administrative control for both young and older males as it can mitigate increases in body heat content during moderate-intensity work-rest cycles in dry heat.

Agreement between measured and self-reported physiological strain in young adults and older adults with and without common chronic diseases during simulated occupational heat stress

While monitoring physiological strain is recommended to safeguard workers during heat exposure, it is logistically challenging. The perceptual strain index (PeSI) is a subjective estimate thought to reflect the physiological strain index (PSI) that requires no direct monitoring. However, advanced age and chronic diseases (hypertension/type 2 diabetes [T2D]) influence the perception of heat stress, potentially limiting the utility of the PeSI. We therefore assessed whether the relation and agreement between the PeSI and PSI during simulated work in various environmental conditions is modified by age and T2D/hypertension. Thirteen young adults and 37 older adults without (n = 14) and with T2D (n = 10) or hypertension (n = 13) walked on a treadmill (∼200 W/m2) for 180 min or until termination (volitional fatigue, rectal temperature ≥39.5 °C) in 16, 24, 28, and 32 °C wet-bulb globe temperatures. Rectal temperature and heart rate were recorded to calculate PSI (0-10 scale). Rating of perceived exertion and thermal sensation were recorded to calculate PeSI (0-10 scale). The relation between hourly PSI and PeSI was assessed via linear mixed models. Mean bias (95% limits of agreement [LoA]) between PSI and PeSI was assessed via Bland-Altman analysis. PSI increased with PeSI (p < 0.001), but the slope of this relation was not different between young and older adults (p = 0.189) or as a function of chronic disease (within older adults; p = 0.183). The mean bias between PSI and PeSI was small (0.02), but the 95% LoA was wide (-3.3-3.4). Together, a linear relation between PeSI and PSI was observed but agreement between these measures varied considerably across individuals and thus PeSI should not be used as a surrogate marker of PSI. Caution should be taken when utilizing the PeSI to estimate physiological strain on workers.

Heat exposure and productivity loss among construction workers: a meta-analysis

BACKGROUND

Global warming is raising increasing concerns about its impact on worker productivity, particularly in industries like construction where outdoor physically demanding jobs are prevalent. This study aimed to perform a meta-analysis to assess the existing evidence on the impact of heat exposure on productivity loss among construction workers.

METHODS

We conducted a comprehensive literature search across six databases-Web of Science, PubMed, Embase, Scopus, ScienceDirect, and IEEE-covering the period from database inception to September 18, 2024. The Joanna Briggs Institute (JBI) critical appraisal checklist was used for quality assessment. A random-effect model meta-analysis was performed, and publication bias was evaluated by Egger's and Begg's tests.

RESULTS

From an initial pool of 1209 studies, 14 met the inclusion criteria, representing data from 2387 workers. Our findings indicate that 60% (95% CI: 0.48-0.72, p < 0.01) of construction workers exposed to elevated temperatures experienced significant productivity loss. Productivity loss was more pronounced when the Wet Bulb Globe Temperature (WBGT) exceeded 28 °C or when ambient temperatures surpassed 35 °C. Furthermore, workers aged over 38 (proportion = 0.61, 95% CI: 0.49-0.72) and teams with female workers (ratio = 0.74, 95% CI: 0.60-0.87) were more susceptible to productivity loss.

CONCLUSIONS

This review highlights heat exposure as a significant factor affecting productivity in the construction industry. We recommend prioritizing the protection of vulnerable groups such as women and older workers, developing innovative technologies and equipment for working in hot conditions, and improving the working environment to safeguard workers' health and productivity. Further research is needed to investigate the long-term health impacts of heat exposure and develop strategies for optimizing microclimate management in construction settings.

Enhancing the effectiveness of heat adaptation strategies through citizen science-based outdoor thermal comfort

Urbanization and intensifying climate change expose populations in cities to escalating heat stress and associated health risks. Mitigating these challenges require comprehensive assessments that combine quantitative and qualitative data to develop effective heat wave response strategies and policies. Previous research has primarily focused on thermal sensation measured by individual biometrics within specific locations. However, limitations in data collection across large areas often lead to the neglect of the influence of diverse urban environments. This may disregard the importance of regional variations and citizen engagement in formulating effective heat wave mitigation strategies. This study explored the impact of heat wave frequency and intensity across various urban spatial types and assessed thermal sensation vote (TSV) among residents of Suwon City using a citizen science approach. Temperature measurements and subjective heat sensations were collected over a three-year period using homemade temperature sensors. The analysis investigated thermal sensation differences across spatial types-open high rise, open low rise, compact mid-rise, urban park, and lake park-utilizing boxplots, and examined TSV variations by age using the R program localized smoothing methodology. Results indicate significant variations in TSV across different urban areas, particularly when temperatures exceeded 32 °C. The TSV was highest in the lake park areas (average thermal sensation vote +3.5) and was comparatively lower in the open high-rise and open low-rise areas (average thermal sensation vote +2.0). A significant age-related trend was observed, with the highest TSV reported by the 19-30 age group. Heat sensitivity appeared to decrease among participants aged 41 and over. These findings highlight the limitations of traditional top-down heatwave response strategies, which may not adequately account for spatial variations and individual experiences. Conversely, a bottom-up approach that leverages citizen science can inform the development of tailored and proactive strategies that consider a region's specific conditions.

Cardiovascular morbidity risk attributable to thermal stress: analysis of emergency ambulance dispatch data from Shenzhen, China

BACKGROUND

Climate change has raised scientific interest in examining the associations of weather conditions with adverse health effects, while most studies determined human thermal stress using ambient air temperature rather than the thermophysiological index.

OBJECTIVES

To evaluate the association between emergency ambulance dispatches (EADs) related to cardiovascular causes and heat/cold stress in Shenzhen, a city in southern China, with the aim of providing new insights for local policymakers.

METHODS

A time series analysis using ambulance dispatch data of cardiovascular diseases in Shenzhen, China (2013-2019) was conducted. A quasi-Poisson nonlinear distributed lag model was applied to explore the relationship between emergency ambulance dispatches (EADs) due to cardiovascular causes and thermal stress (determined by Universal Thermal Climate Index, UTCI). Attributable fractions were estimated to identify which UTCI ranges have a greater health impact.

RESULTS

The relationship between UTCI and EADs due to cardiovascular diseases exhibits a reverse J-shaped curve. The effects of cold stress were immediate and long-lasting, whereas the effects of heat stress were non-significant. Compared with the optimal equivalent temperature (71st percentile of UTCI, 29.22 °C), the relative risks for cumulative (0-21 days) exposures to cold stress (1st percentile, - 0.13 °C; 5th percentile, 7.68 °C) were 1.55 (95%CI:1.28,1.88) and 1.44 (95%CI:1.22,1.69), respectively. Thermal (cold and heat) stress was responsible for 10.81% (95%eCI: 5.67%,15.43%) of EADs for cardiovascular diseases, with 9.46% (95%eCI: 3.98%,14.40%) attributed to moderate cold stress (2.5th ~ 71st percentile). Greater susceptibility to cold stress was observed for males and the elderly. Heat stress showed harmful effects in the warm season.

CONCLUSIONS

Our results demonstrated that cold exposure elevates the risk of EADs for cardiovascular causes in Shenzhen, and moderate cold stress cause the highest burden of ambulance dispatches. Health authorities should consider effective adaptation strategies and interventions responding to cold stress to reduce the morbidity of cardiovascular diseases.

The combined effects of heatwaves, air pollution and greenery on the risk of frailty: a national cohort study

The associations between heatwaves and frailty, as well as the joint effects of heatwaves with air pollution and greenery, are currently unknown. This study leverages data from the China Health and Retirement Longitudinal Study (CHARLS), which collected information from 6,400 older adults between 2011 and 2018. Our outcome variable was frailty, as measured by the frailty index (FI > 0.21). Heatwaves were defined based on maximum temperature, incorporating four thresholds (≥ 97.5%, 97.5%, 92.5%, and 90%) and three durations (≥ 2, 3, and 4 days). These variables were considered as time-varying variables, representing the one-year exposure preceding survival events. Fine particulate matter (PM2.5) and greenery (normalized difference vegetation index (NDVI)) were utilized as indicators of air pollution and greenery exposure, respectively, and were treated as time-varying indicators concurrent with heatwaves.Time-varying Cox proportional hazards models were employed to assess the independent effects, as well as the multiplicative and additive interactions of heatwaves, air pollution, and greenery on the risk of frailty. These effects were quantified using hazard ratios (HRs), a traditional product term representing the ratio of HRs, and the relative excess risk due to interaction (RERI). Our findings indicate that heatwaves are associated with an increased risk of frailty, with HRs ranging from 1.035 (95% CI: 1.006-1.064) to 1.063 (95% CI: 1.028-1.101). We observed both a positive multiplicative interaction (HRs > 1) and an additive interaction (RERI > 0) between high level PM2.5 concentration, lack of greenery, and heatwaves. This study reveals that the combined effects exacerbate the adverse impact of heatwaves on the risk of frailty. Moreover, the combined effects of heatwaves, air pollution, and greenery exposure on frailty risk vary across age, gender, and educational attainment.

Climate change's implications for practice: Pharmacologic considerations of heat-related illness

ABSTRACT

Climate change is the greatest threat to global health. As climate change worsens, heat waves will be longer, more intense, and more frequent. Increased health risks from climate change and heat waves include heat-related illness (HRI). HRI increases ED visits, hospitalizations, and mortality. Healthcare providers should be aware of the impact of medications on risk for HRI. This article elucidates signs and symptoms, populations at risk, drugs and mechanisms that increase risk, and patient education to reduce risk.

Thermal Comfort Conditions and Mortality in Brazil

Conventional temperature-based approaches often overlook the intricate nature of thermal stress experienced by individuals. To address this limitation, climatologists have developed thermal indices-composite measures designed to reflect the complex interaction of meteorological factors influencing human perception of temperature. Our study focuses on Brazil, estimating the association between thermal comfort conditions and mortality related to respiratory and circulatory diseases. We examined four distinct thermal indices: the discomfort index (DI), net effective temperature (NET), humidex (H), and heat index (HI). Analyzing a comprehensive dataset of 2,872,084 deaths from 2003 to 2017, we found significant variation in relative risk (RR) based on health outcomes, exposure lag, percentile of exposure, sex/age groups, and specific thermal indices. For example, under high exposure conditions (99th percentile), we observed that the shorter lags (3, 5, 7, and 10) had the most robust effects on all-cause mortality. For example, under lag 3, the pooled national results for the overall population (all ages and sexes) indicate an increased risk of all-cause mortality, with an RR of 1.17 (95% CI: 1.13; 1.122) for DI, 1.15 (95% CI: 1.12; 1.17) for H, 1.15 (95% CI: 1.09; 1.21) for HI, and 1.18 (95% CI: 1.13; 1.22) for NET. At low exposure levels (1st percentile), all four distinct thermal indices were linked to an increase in all-cause mortality across most sex and age subgroups. Specifically, for lag 20, we observed an estimated RR of 1.19 (95% CI: 1.14; 1.23) for DI, 1.12 (95% CI: 1.08; 1.16) for H, 1.17 (95% CI: 1.12; 1.22) for HI, and 1.18 (95% CI: 1.14; 1.23) for NET. These findings have important implications for policymakers, guiding the development of measures to minimize climate change's impact on public health in Brazil.

Foot immersion with and without neck cooling reduces self-reported environmental symptoms in older adults exposed to simulated indoor overheating

While foot immersion and neck cooling have been recommended for protecting heat-vulnerable groups, recent evidence does not support their efficacy for mitigating increases in physiological heat strain in older adults. However, their influence on self-reported environmental symptoms and mood-state remains unclear. Seventeen older adults (nine females, median [interquartile range] age: 72 [69-74]) completed three randomized heat exposures (6-h; 38°C, 35% relative humidity) with no cooling (control), foot immersion to mid-calf in 20°C water for the final 40-min of each hour (foot immersion), or foot immersion with a wet towel (20°C) around the neck (foot immersion with neck cooling). Core temperature, skin temperature, and heart rate areas under the curve (AUC) were assessed as indicators of cumulative physiological strain. Environmental symptom scores (68-item environmental symptoms questionnaire) and mood disturbance (40-item profile of mood states questionnaire) were evaluated at end-heating (adjusted for pre-exposure). Core temperature AUC was not different between conditions (p = 0.418). However, the skin temperature and heart rate AUCs were 11.8°C · h [95% confidence interval: 8.1, 15.5] and 12.5 bpm · h [0.1, 24.8] lower for foot immersion and 16.6°C · h [12.9, 20.3] and 19.6 bpm · h [7.2, 32.0] lower for foot immersion with neck cooling compared to control (p ≤ 0.032). Environmental symptom scores were 0.8-fold [0.6, 1.0] lower for both foot immersion with and without neck cooling, compared to control (both p = 0.036). Mood disturbance was not different between conditions (both p ≥ 0.275). Foot immersion with and without neck cooling reduces self-reported environmental symptoms in older adults despite having little effect on physiological heat strain.

Markers of enterocyte damage, microbial translocation, and systemic inflammation following 9 h of heat exposure in young and older adults

Heat stress induced damage to the gastrointestinal barrier can induce local and systemic inflammatory reactions implicated in heat-stroke. Gastrointestinal barrier damage has been shown to be greater in older relative to young adults following hyperthermia. However, comparisons between young and older adults have been limited to brief exposures (3 h), which may not reflect the duration of heat stress experienced during heat waves. We therefore evaluated markers of intestinal epithelial damage (log transformed intestinal fatty acid binding protein, IFABPLOG), microbial translocation (soluble cluster of differentiation 14, sCD14LOG), and systemic inflammation (tumour necrosis factor alpha, TNF-αLOG; interleukin 6, IL-6LOG; C-reactive protein, CRP) in 19 young (interquartile range: 21-27 years; 10 females) and 37 older (68-73 years; 10 females) adults before and after 9 h of rest in 40 °C (9% relative humidity). The magnitude of the increase in IFABPLOG was 0.38 log pg/mL (95% CI, 0.10, 0.65 log pg/mL) greater in the older relative to young cohort (P = 0.049) after 9 h heat exposure. At baseline both IL-6LOG and CRP concentrations were higher in the older (IL-6: 2.67 (1.5) log pg/mL, CRP: 0.28 (1.5) mg/mL) relative to the young (IL-6: 1.59 log pg/mL, SD 1.2; CRP: 0.11 mg/mL, SD 1.7) group (both P ≤ 0.001). The change in IL-6 and CRP was similar between groups following 9 h heat exposure (IL-6: P = 0.053; CRP: P = 0.241). Neither sCD14LOG and TNF-αLOG were different between groups at baseline nor altered after 9 h heat exposure. Our data indicate that age may modify intestinal epithelial injury following 9 h of passive heat exposure.

Senior Health in a Changing Climate: Unique Needs of a Complex Population

Health effects of climate change present different challenges to people as they age, and the risks are expected to be higher in lower-income countries. Protective actions can help.

Time to reach equilibrium deep body temperatures in young and older adults resting in the heat: a descriptive secondary analysis

It is commonly thought that steady-state thermoregulatory responses are achieved within 30-90 min of compensable heat stress. However, this assumption is based on measurements of whole body heat exchange during exercise, which stabilize (equilibrate) more rapidly than deep body temperatures, especially under resting conditions. To support the design of ecologically relevant heat exposure studies, we quantified equilibrium times for deep body temperature, as indexed by rectal temperature, in young and older adults resting in the heat. We also evaluated the lag in rectal temperature equilibrium relative to whole body heat storage (direct calorimetry). Equilibrium times were estimated with data from two laboratory-based trials (NCT04353076 and NCT04348630) in which 83 adults aged 19-80 yr (34 female) were exposed to simulated heat-wave conditions for 8-9 h. When assessed at the group level, it took rectal temperature 3.3 [bootstrap 95% confidence interval: 2.9-3.9] h to reach thermal equilibrium (<0.05°C/h rate of change) in young adults exposed to 40°C, 9% relative humidity (RH). In older adults, who were exposed to a greater range of conditions (31°C-40°C, 9-45% RH), equilibrium times were longer, ranging from 4.4 [3.8-5.3] to 5.2 [4.9-5.4] h. Furthermore, rectal temperature equilibrium was delayed 0.9 [0.5-1.4] and 1.8 [0.9-2.7] h compared with whole body heat storage in young and older adults, respectively (only assessed in 40°C, 9% RH). Individual-level equilibrium times ranged from 1 to 8 h. These findings highlight the importance of ecologically relevant exposure durations in translational research assessing the physiological impacts of hot weather.NEW & NOTEWORTHY Deep body (rectal) temperature took 3-5 h on average and up to 6-8 h at the individual level to reach thermal equilibrium in young and older adults resting in the heat. Furthermore, stable rectal temperatures were delayed by up to 2 h relative to the achievement of heat balance (0 kJ/min rate of heat storage). We provide the first quantification of the temporal profiles of thermal strain during extended rest in conditions simulating hot weather.

NPCC4: Climate change and New York City's health risk

This chapter of the New York City Panel on Climate Change 4 (NPCC4) report considers climate health risks, vulnerabilities, and resilience strategies in New York City's unique urban context. It updates evidence since the last health assessment in 2015 as part of NPCC2 and addresses climate health risks and vulnerabilities that have emerged as especially salient to NYC since 2015. Climate health risks from heat and flooding are emphasized. In addition, other climate-sensitive exposures harmful to human health are considered, including outdoor and indoor air pollution, including aeroallergens; insect vectors of human illness; waterborne infectious and chemical contaminants; and compounding of climate health risks with other public health emergencies, such as the COVID-19 pandemic. Evidence-informed strategies for reducing future climate risks to health are considered.

Identifying groups at-risk to extreme heat: Intersections of age, race/ethnicity, and socioeconomic status

Anthropogenic climate change has resulted in a significant rise in extreme heat events, exerting considerable but unequal impacts on morbidity and mortality. Numerous studies have identified inequities in heat exposure across different groups, but social identities have often been viewed in isolation from each other. Children (5 and under) and older adults (65 and older) also face elevated risks of heat-related health impacts. We employ an intersectional cross-classificatory approach to analyze the distribution of heat exposure between sociodemographic categories split into age groups in the contiguous US. We utilize high-resolution daily air temperature data to establish three census tract-level heat metrics (i.e., average summer temperature, heat waves, and heat island days). We pair those metrics with American Community Survey estimates on racial/ethnic, socioeconomic, and disability status by age to calculate population weighted mean exposures and absolute disparity metrics. Our findings indicate few substantive differences between age groups overall, but more substantial differences between sociodemographic categories within age groups, with children and older adults from socially marginalized backgrounds facing greater exposure than adults from similar backgrounds. When looking at sociodemographic differences by age, people of color of any age and older adults without health insurance emerge as the most exposed groups. This study identifies groups who are most exposed to extreme heat. Policy and program interventions aimed at reducing the impacts of heat should take these disparities in exposure into account to achieve health equity objectives.