Expert Commentary

How heat waves affect older people

To help reporters covering how heat waves affect the elderly, Journalist’s Resource has collected recent research on the subject.

heat wave sun

Heat waves are expected to occur with increasing frequency, and older people are particularly imperiled by extreme summer temperatures.

This added vulnerability stems in part from the fact that older people are more likely to have chronic medical conditions that modify the body’s ability to adapt to heat; they are more likely to take medications that play a role in these processes as well. For example, the United States Environmental Protection Agency has reported that since 1999, “people aged 65+ have been several times more likely to die from heat-related cardiovascular disease than the general population.”

To help reporters who may be writing stories about how heat waves affect the elderly on a local, national or international level, Journalist’s Resource collected research on the subject, including studies on the changing climate’s heat-related health effects, associated costs, which heat waves are most dangerous and potential interventions to mitigate these effects.


Heatwave and Elderly Mortality: An Evaluation of Death Burden and Health Costs Considering Short-Term Mortality Displacement
Cheng, Jian; et al. Environment International, 2018. DOI: 10.1016/j.envint.2018.03.041.

Results: “Among the Australian elderly population, we found significant associations between heatwave and deaths, with raised mortality immediately in the first few days followed by lower-than-expected mortality. In general, heatwave was associated with an average death increase of 28 percent (95 percent confidence interval (CI): 15 percent to 42 percent), and greater increases were mostly observed for more intense heatwaves across multiple megacities. During the study period, there were dozens to hundreds of deaths attributable to heatwave for each city, equating to an economic loss of several million Australian dollars every year. Although the estimated attributable deaths varied by heatwave intensity and duration, the pattern was not consistent across cities.”

Association Between High Environmental Heat and Risk of Acute Kidney Injury Among Older Adults in a Northern Climate: A Matched Case-Control Study
McTavish, Rebecca K.; et al. American Journal of Kidney Diseases, 2018. DOI: 10.1053/j.ajkd.2017.07.011.

Abstract: “An association between high heat and acute kidney injury (AKI) has been reported in warm climates. However, whether this association generalizes to a northern climate, with more variable temperatures, is unknown. … Heat periods were significantly associated with higher risk for AKI (adjusted odds ratio (OR), 1.11; 95 percent CI, 1.00-1.23). Heat periods in absolute terms were associated with an additional 182 cases of AKI per 100,000 person-years during the warm season.”

A Geographical Analysis of Emergency Medical Service Calls and Extreme Heat in King County, WA, USA (2007–2012)
DeVine, Aubrey; et al. International Journal of Environmental Research and Public Health, 2017. DOI: 10.3390/ijerph14080937.

Abstract: “This research analyzed the relationship between extreme heat and Emergency Medical Service (EMS) calls in King County, WA, USA between 2007 and 2012, including the effect of community-level characteristics. Extreme heat thresholds for the Basic Life Support (BLS) data and the Advanced Life Support (ALS) data were found using a piecewise generalized linear model with Akaike Information Criterion (AIC). … We conclude that EMS call volume increases significantly on a heat day compared to non-heat day for both call types. While this study shows that there is some effect modification between the community-level variables and call volume on a heat day, further research is necessary. Our findings also suggest that with adequate power, spatially refined analyses may not be necessary to accurately estimate the extreme-heat effect on health.”

Summertime Acute Heat Illness in U.S. Emergency Departments from 2006 through 2010: Analysis of a Nationally Representative Sample
Hess, Jeremy J.; et al. Environmental Health Perspectives, 2014. DOI: 10.1289/ehp.1306796.

Conclusions: “Heat illness presented to the emergency department (ED) frequently, with highest rates in rural areas. Case definitions should include all diagnoses. Visit rates were correlated with temperature anomalies. Heat stroke had a high ED CFR (case fatality rate). Males, elders, and the chronically ill were at greatest risk of admission or death in the ED. Chronic disease burden exponentially increased this risk.”

Global Climate Change: Impact of Heat Waves under Different Definitions on Daily Mortality in Wuhan, China
Zhang, Yunquan, et al. Global Health Research and Policy, 2017. DOI: 10.1186/s41256-017-0030-2.

Abstract: “There was no consistent definition for heat wave worldwide, while a limited number of studies have compared the mortality effect of heat wave as defined differently. This paper aimed to provide epidemiological evidence for policy makers to determine the most appropriate definition for local heat wave warning systems. We developed 45 heat wave definitions (HWs) combining temperature indicators and temperature thresholds with durations. We then assessed the impact of heat waves under various definitions on non-accidental mortality in hot season (May–September) in Wuhan, China during 2003–2010. Heat waves defined by HW14 (daily mean temperature ≥ 99.0th percentile and duration ≥ 3 days) had the best predictive ability in assessing the mortality effects of heat wave with the relative risk of 1.63 (95 percent CI: 1.43, 1.89) for total mortality. The group-specific mortality risk using official heat wave definition of Chinese Meteorological Administration was much smaller than that using HW14. We also found that women, and the elderly (age ≥ 65) were more susceptible to heat wave effects which were stronger and longer lasting.”

Projecting Future Climate Change Impacts on Heat-Related Mortality in Large Urban Areas in China
Li, Ying; et al. Environmental Research, 2018. DOI: 10.1016/j.envres.2018.01.047.

Abstract: “… This is an exploratory study aimed at projecting future heat-related mortality risk in major urban areas in China. We focus on the 51 largest Chinese cities that include about one third of the total population in China, and project the potential changes in heat-related mortality based on 19 different global-scale climate models and three Representative Concentration Pathways (RCPs). City-specific risk estimates for high temperature and all-cause mortality were used to estimate annual heat-related mortality over two future twenty-year time periods. We estimated that for the 20-year period in Mid-21st century (2041–2060) relative to 1970–2000, incidence of excess heat-related mortality in the 51 cities to be approximately 37,800 (95 percent CI: 31,300–43,500), 31,700 (95 percent CI: 26,200–36,600) and 25,800 (95 percent CI: 21,300–29,800) deaths per year under RCP8.5, RCP4.5 and RCP2.6, respectively. Slowing climate change through the most stringent emission control scenario RCP2.6, relative to RCP8.5, was estimated to avoid 12,900 (95 percent CI: 10,800–14,800) deaths per year in the 51 cities in the 2050s, and 35,100 (95 percent CI: 29,200–40,100) deaths per year in the 2070s. The highest mortality risk is primarily in cities located in the North, East and Central regions of China. Population adaptation to heat is likely to reduce excess heat mortality, but the extent of adaptation is still unclear. Future heat mortality risk attributable to exposure to elevated warm season temperature is likely to be considerable in China’s urban centers, with substantial geographic variations. Climate mitigation and heat risk management are needed to reduce such risk and produce substantial public health benefits.”

The Health Effects of Hotter Summers and Heat Waves in the Population of the United Kingdom: A Review of the Evidence
Arbuthnott, Katherine G.; Hajat, Shakoor. Environmental Health, 2017. DOI: 10.1186/s12940-017-0322-5.

Abstract: “It is widely acknowledged that the climate is warming globally and within the UK. In this paper, studies which assess the direct impact of current increased temperatures and heat-waves on health and those which project future health impacts of heat under different climate change scenarios in the UK are reviewed. This review finds that all UK studies demonstrate an increase in heat-related mortality occurring at temperatures above threshold values, with respiratory deaths being more sensitive to heat than deaths from cardiovascular disease (although the burden from cardiovascular deaths is greater in absolute terms). The relationship between heat and other health outcomes such as hospital admissions, myocardial infarctions and birth outcomes is less consistent. We highlight the main populations who are vulnerable to heat. Within the UK, these are older populations, those with certain co-morbidities and those living in Greater London, the South East and Eastern regions.”

Heat-Related Hospitalizations in Older Adults: An Amplified Effect of the First Seasonal Heatwave
Liss, Alexander; et al. Scientific Reports, 2017. DOI: 10.1038/srep39581.

Abstract: “Older adults are highly vulnerable to the detriment of extreme weather. The rapid non-linear increase in heat-related morbidity is difficult to quantify, hindering the attribution of direct effects of exposure on severe health outcomes. We examine the effects of ambient temperatures on heat-related hospitalizations (HH) among the elderly in presence of strong seasonality and by assessing the effects caused by the first and subsequent seasonal heatwaves. We empirically derived the thresholds for a heatwave episode in Boston [metropolitan statistical area] based on 16 years of daily observations. We compared the health risks of heatwaves using the proposed and four alternative definitions. 701 cases of HH in older residents of Boston area were examined using harmonic regression models, designed to capture the non-linear effects of ambient temperatures and heatwave episodes when the night-time temperature is above 65.5 °F for 3 consecutive nights. The overall relative risk of HH associated with a heatwave episode was 6.9 [95 percent CI: 4.8–9.8]. The relative risk of HH associated with the first heatwave increases up to 13.3 [95 percent CI: 7.4–24.0]. The risk declined to 3.7 [95 percent CI: 2.4–5.8] for the subsequent heatwave. Four other commonly used heatwave definitions confirmed these findings. Public health actions have to target the first heatwave to maximize the impact of preventive measures.”

Development of a Heat Vulnerability Index for New York State
Nayak, S. G.; et al. Public Health, 2017. DOI: 10.1016/j.puhe.2017.09.006.

Abstract: “The frequency and intensity of extreme heat events are increasing in New York State (NYS) and have been linked with increased heat-related morbidity and mortality. But these effects are not uniform across the state and can vary across large regions due to regional sociodemographic and environmental factors which impact an individual’s response or adaptive capacity to heat and in turn contribute to vulnerability among certain populations. We developed a heat vulnerability index (HVI) to identify heat-vulnerable populations and regions in NYS.”

Heatwave and Health Events: A Systematic Evaluation of Different Temperature Indicators, Heatwave Intensities and Durations
Xu, Zhiwei; et al. Science of the Total Environment, 2018. DOI: 10.1016/j.scitotenv.2018.02.268.

Findings: “Mean temperature was slightly better than maximum temperature in predicting heatwave impact on morbidity (P < 0.05), and no appreciable difference in model performance was observed amongst different mean temperature indicators. Two-day-duration heatwaves were more detrimental than longer-lasting heatwaves when heatwave intensity was not high, and 97th percentile appeared to be a consistent temperature threshold for most heatwave-related health events (P < 0.05).”

Heat and Adult Health in China
Mueller, Valerie; Gray, Clark. Population and Environment, 2018. DOI: 10.1007/s11111-018-0294-6.

Abstract: “Given projected increases in the frequency of precipitation and temperature extremes in China, we examine the extent adults may be vulnerable to climate anomalies. We link nutrition, health, and economic data from the China Health and Nutrition Survey (1989–2011) to gridded climate data to identify which socioeconomic outcomes are particularly susceptible, including adult underweight incidence, body mass index, dietary intake, physical activity, illness, income, and food prices. We find warm temperatures augment the probability of being underweight among adults, with a particularly large impact for the elderly (ages > 60). Extremely dry and warm conditions produce a 3.3-percentage point increase in underweight status for this group. Consequences on nutrition coincide with changes in illness rather than dietary, income, or purchasing power shifts. Social protection targeting areas prone to excessive heat may consider supplementing bundles of goods with a suite of health care provisions catering to the elderly.”

Social Interventions to Prevent Heat-Related Mortality in the Older Adult in Rome, Italy: A Quasi-Experimental Study
Liotta, Giuseppe; et al. International Journal of Environmental Research and Public Health, 2018. DOI: 10.3390/ijerph15040715.

Abstract: “This study focuses on the impact of a program aimed at reducing heat-related mortality among older adults residing in central Rome by counteracting social isolation. The mortality of citizens over the age of 75 living in three Urban Areas (UAs) located in central Rome is compared with that of the residents of four adjacent UAs during the summer of 2015. The data, broken down by UA, were provided by the Statistical Office of the Municipality of Rome, which gathers them on a routine basis. During the summer of 2015, 167 deaths were recorded in those UAs in which the Long Live the Elderly (LLE) program was active and 169 in those in which it was not, implying cumulative mortality rates of 25‰ (SD ± 1.4; Cl 95 percent: 23–29) and 29‰ (SD ± 6.7; Cl 95 percent: 17–43), respectively. Relative to the summer of 2014, the increase of deaths during the summer of 2015 was greater in UAs in which the LLE program had not been implemented (+97.3 percent vs. +48.8 percent). In conclusion, the paper shows the impact of a community-based active monitoring program, focused on strengthening individual relationship networks and the social capital of the community, on mortality in those over 75 during heat waves.”

Related research:  Please see our summary of a study on who among the elderly is most vulnerable to wildfire smoke

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