Urban Heat Islands and Heat-Related Cardiovascular Morbidity in Older Adults: A Time Series Study of US Metropolitan Areas
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Background and Aim. Extreme heat increases the risk of hospitalization due to cardiovascular disease (CVD). The United States (US) population largely resides in urban areas where climate change is projected to increase temperatures, yet little is known about this association across urban heat islands (UHIs). We aimed to identify the urban populations most at risk of and burdened by heat-related CVD morbidity.
Methods. We obtained daily counts of CVD hospital admissions (HAs) for Medicare enrollees (aged 65+) in 120 metropolitan areas (MSAs) in the contiguous US between 2000-2017. Daily average temperatures were estimated through the interpolation of monitor observations. A measure of UHI intensity was estimated from satellite-derived temperatures in urban vs. non-urban areas. We used quasi-Poisson regression with distributed-lag, non-linear models to estimate MSA-specific associations and pooled these estimates with multivariate meta-analyses. Stratified analyses were performed by UHI intensity quartile. We also calculated the number of CVD HAs attributable to heat in each MSA.
Results. Overall, extreme heat (99th percentile, ~28.6°C) was associated with a 3.0% [1.4%, 4.6%] increase in CVD HA risk relative to the minimum hospitalization temperature (MHT) (91st percentile, ~25.4°C). MSA-specific risks showed substantial differences, with higher risk in MSAs with lower annual average temperatures. We estimate that 1.6% (31,498) of CVD HAs on days above the MHT were attributable to heat. Although the interquartile risk differences were not significant, the highest quartile of UHI intensity was responsible for 47% (14,636) of all heat-attributable CVD HAs.
Conclusions. Our results show that extreme heat increases the risk of CVD HAs among older adults in US urban areas, with considerable variation between cities. Areas with higher UHI intensity had the highest heat-related burden, indicating a potentially vulnerable subset of the urban population. This abstract does not necessarily reflect EPA policy.