Climate Change Health Impacts: Extreme Heat, Heat Waves and Hospitalizations

November 5, 2014

Link to Article Reviewed:

Extreme heat events are anticipated to grow in number, intensity and length of duration as the effects of climate change increase over time. Increases in events such as heat waves from climate change could have large health implications on the elderly which are the most susceptible populations. Health studies of extreme heat and heat waves have focused predominantly on mortality outcomes, which may not adequately account for the burden on the US healthcare systems like Medicare that service the most susceptible population. Studies like the one by Gronlund et al., (2014) that focus on hospital admissions have the potential to improve our understanding of the future heat-related morbidity amongst overburdened populations and provide an opportunity to develop and focus interventions amongst susceptible populations.

In this article researchers analyzed the effect of moderate heat and extreme heat from May-September (warm season) defined as the 90th and 99th percentile of mean apparent temperature on all-cause and specific-cause hospitalizations. The contribution of heat waves defined as 2, 4, 6 and 8 consecutive days with mean temperature at 95% or above the city-specific warm season was also examined for influence on the relationship between extreme heat and hospitalization. Medicare emergency room admission for hospitalization during the warm season months on adults ≥ 65years of age were used to examine the effect of daily heat and durations of heat waves from 2-8 days on cardiovascular, respiratory, renal and total all-cause hospitalizations in 114 cities across the United States from 1992-2006. An interesting secondary analysis of this manuscript is the inclusion of ozone as a confounding variable since it is associated with both high temperatures and hospitalizations; additional analyses were run that controlled for this air pollutant.

Overall extreme heat and heat waves were observed to have the largest effect on renal hospitalizations.  Single day lags for hospitalizations due to the extreme heat (99th versus 75th percentile mean temperature) were associated with all-cause, renal and respiratory hospitalizations, but not cardiovascular hospitalizations. Analysis for effects of moderate heat (90th versus 75th percentile mean temperature) found associations with single day and weeklong lags with all-cause, renal and respiratory (0-1 day lag was only significant group).  However the size of the effect that extreme heat had on hospitalizations was approximately 2-3 times that of moderate heat. Analysis for effect of heat wave was summed with the main effects of extreme heat producing a positive linear association between renal hospitalizations and heat wave duration of 2, 4, 6 & 8 days. Or, an increase in the number of days in the heat wave had a corresponding increase in the trend for renal hospitalization. These results indicate that days of extreme heat can increase hospitalizations, but that the effects are magnified during a prolonged heat wave.  

Climate change is predicted to increase the frequency and duration of extreme heat events over time, indicating a need to better understand the anticipated burden on health systems especially with an expanding elderly population. The implication of these results can be applied to both current and future health benefits and research: 1) “Elderly individuals with respiratory and especially renal conditions, and providers of services to such people, may benefit from taking additional precautions when heat warnings are issued”. 2)  Climate change reduction and adaptation strategies should consider simultaneously including enhancements and mechanisms to deal with public health preparedness that “may play important roles in determining the extent to which extreme heat puts the health of older people at risk in any given community”.  Some of these mechanisms include increased vegetative and albedo surface reflectance, housing stock, access to air conditioning and cooling center deployment plans. However, it is recognized by these authors as well as other researchers that further exploration is needed to examine the contributions of these strategies to mitigate heat-related health impacts.


Citation: Gronlund CJ, Zanobetti A, Schwartz JD, Wellenius GA, O’Neill MS. Heat, Heat Waves, and Hospital Admissions among the Elderly in the United States, 1992–2006. Environmental Health Perspectives, 2014; 122(11):1187-1192.

If you liked this article and topic, I recommend:

Anderson GB, Dominici F, Wang Y, McCormack MC, Bell ML, Peng RD. 2013. Heat-related emergency hospitalizations for respiratory diseases in the Medicare population. Am J Respir Crit Care Med 187:1098–1103.

Zanobetti A, O’Neill MS, Gronlund CJ, Schwartz JD. 2012. Summer temperature variability and long-term survival among elderly people with chronic disease. Proc Natl Acad Sci USA 109:6608–6613.