# Extreme Heat, Social Factors, and Mortality Among California Veterans With Cardiometabolic Disease

## TL;DR

Extreme heat increases mortality risk for California veterans with heart and metabolic diseases, especially those in disadvantaged areas or who are homeless.

## Contribution

This study is the first to investigate how extreme heat affects mortality in veterans with cardiometabolic diseases and how social factors modify this risk.

## Key findings

- Extreme heat events were significantly linked to higher mortality risk among veterans with cardiometabolic diseases.
- Veterans in lower socioeconomic neighborhoods and those who are homeless showed higher mortality risk during heat events.
- Effect estimates were greater for veterans in high deprivation areas and those experiencing homelessness.

## Abstract

Are extreme heat events (EHEs) associated with increased risk of mortality among California veterans with cardiometabolic disease?

In this time-stratified case-crossover study of 13 556 US veterans, EHEs were significantly associated with increased risk of mortality for same-day EHEs at the 95th percentile of historical mean temperatures. Veterans residing in lower socioeconomic status (SES) neighborhoods and veterans experiencing homelessness had increased risk of mortality compared with those living in higher SES neighborhoods and housed veterans, respectively, although these differences were not statistically significant.

This study suggests that the Veterans Health Administration should consider the increasing threat of EHEs for veteran communities at highest risk.

There is limited research investigating associations between extreme heat events (EHEs) and adverse outcomes for veterans and high-risk veteran subpopulations.

To investigate the association between EHEs and mortality among California veterans with common cardiometabolic diseases and to examine how this risk differs by race and ethnicity, neighborhood health-related social risk factors, and history of homelessness.

This case-crossover study used administrative data from the Veterans Health Administration (VA) Corporate Data Warehouse to identify veterans with a California address from October 1, 2015, to September 30, 2021, and a diagnosis of a cardiometabolic condition of hypertension, diabetes, ischemic heart disease, congestive heart failure, chronic kidney disease, stroke, or peripheral arterial disease. Data were analyzed from October 2023 to December 2024.

Date- and address-specific EHEs as defined by daily maximum temperatures greater than the 90th, 95th, and 97.5th percentiles of 2006 to 2020 historical normal temperatures derived from National Center for Environmental Information meteorological data. Patient residential addresses were linked with the nearest weather station. The associations of same-day to 4-day EHEs with mortality were assessed.

The main outcome was individual all-cause mortality during warm months (April-October). A time-stratified case-crossover design with conditional logistic regression was used to investigate associations between EHEs and mortality. Planned exploratory subgroup analyses were performed by race and ethnicity, Area Deprivation Index (ADI) for patient address, and homeless status.

A total of 13 556 veterans (median age, 78 years [IQR, 71-87 years]; 13 265 men [97.9%]) experienced mortality during the study period. Extreme heat events were significantly associated with mortality at all percentile thresholds (eg, at 95th percentile odds ratio [OR] range, 1.10 [95% CI, 1.04-1.17] to 1.14 [95% CI, 1.08-1.20]; P = .005). Effect estimates were greater for veterans in high vs lower ADI neighborhoods (eg, 3-day EHEs at 95th percentile: OR, 1.44 [95% CI, 1.15-1.80] vs OR, 1.12 [95% CI, 1.06-1.19]), and veterans who experienced homelessness compared with those who did not (eg, 3-day EHEs at 95th percentile: OR, 1.25 [95% CI, 1.09-1.45] vs OR, 1.12 [95% CI, 1.05-1.19]) across EHE definitions, although there was no statistically significant effect modification.

In this study of California veterans with common cardiometabolic diseases, EHEs were significantly associated with mortality. These results suggest that the VA should develop EHE risk-mitigating interventions to protect veterans, particularly those at greatest risk, from heat-related mortality.

This case-control study with a case-crossover design investigates the association between extreme heat events and mortality among California veterans with cardiometabolic disease and examines how this risk differs by race and ethnicity, neighborhood health-related social risk factors, and history of homelessness.