Extreme Heat Greatly Increases Death Risk for California Veterans Living With Cardiometabolic Conditions
A new study has raised serious concerns about how extreme heat affects veterans in California, especially those living with cardiometabolic conditions such as hypertension, diabetes, ischemic heart disease, congestive heart failure, chronic kidney disease, stroke, or peripheral arterial disease. Conducted by researchers at UCLA and the VA Greater Los Angeles Healthcare System, the work highlights how dangerously vulnerable many veterans are becoming as heat waves intensify across the state.
The study, recently published in JAMA Network Open, examined data from fiscal years 2016 through 2021 and focused specifically on veterans with at least one cardiometabolic condition. These conditions already strain the heart and circulatory system, and when combined with extreme heat, the risk becomes even more severe. The research team used a time-stratified case-crossover design, analyzing administrative and electronic health records from the VA Corporate Data Warehouse.
During the study window, 13,556 California veterans with underlying cardiometabolic conditions died. Their median age was 78, and nearly 98% were men. The researchers examined what the weather was like on the day each veteran died and compared it with control days that were similar in every respect except temperature. This allowed them to isolate the effect of extreme heat on mortality.
What they found is worrying: during extreme heat events (EHEs)—defined as days when temperatures rose above the 95th percentile of historical averages—veterans had a 10% to 14% higher risk of dying compared to cooler days. And when heat waves lasted multiple consecutive days, the elevated risk persisted. For example, a 3-day EHE at the 95th percentile was linked to significantly higher odds of mortality.
The study also revealed important differences among subgroups of veterans. Those living in high-disadvantage neighborhoods, identified by the Area Deprivation Index (ADI), faced an even greater risk. For a 3-day extreme heat event, the odds of death among high-ADI veterans were 44% higher, compared with 12% higher among veterans living in more affluent areas. Veterans who had experienced homelessness were also more vulnerable: they had roughly a 25% increase in mortality risk during extreme heat compared with 12% among housed veterans. Although these subgroup differences did not reach statistical significance, they still reveal meaningful patterns that highlight how social conditions intersect with health risks.
So why are veterans at such high risk? The study provides several reasons. Veterans enrolled in the VA health system tend to be older, making them more susceptible to heat-related stress. They also have higher rates of chronic disease, particularly cardiometabolic conditions that can impair the body’s ability to regulate temperature. Additionally, many veterans take medications—such as diuretics, beta blockers, and certain antihypertensives—that can interfere with hydration, sweating, or cardiovascular responses during high heat.
On top of these medical factors, many veterans live in urban heat islands, dense city environments that absorb and trap heat. Veterans who are unhoused face some of the worst conditions, often without consistent access to cooling centers, shade, or air-conditioned indoor spaces. These overlapping risks create a dangerous situation whenever temperatures spike.
Of course, every study comes with limitations, and the researchers were clear about theirs. One major caveat is that they assumed, but could not confirm, that veterans were at or near their residential address on the day of death. Actual heat exposure varies depending on where someone physically is. The researchers also had no data on indoor temperatures—whether veterans had access to air conditioning, whether they lived in poorly insulated buildings, or whether cooling systems were functioning. Additionally, the study’s definition of homelessness did not distinguish between sheltered and unsheltered homelessness, which are vastly different experiences in terms of heat exposure. And finally, because the study only focused on California, the findings may not perfectly generalize to veterans in regions with different climates.
Despite these limitations, the takeaway is clear: extreme heat poses a real and measurable threat to veterans with cardiometabolic conditions. As climate change continues to increase the frequency and severity of heat waves, these risks are expected to grow.
The researchers emphasize that the VA and other healthcare systems must build emergency plans and long-term strategies to protect vulnerable populations during heat events. This includes broader outreach to veterans living in disadvantaged communities, targeted support for homeless veterans, and public health tools that help identify at-risk individuals ahead of dangerous heat spells.
Future work by the team will look beyond mortality, examining whether extreme heat is associated with hospitalizations and emergency department visits across both VA and non-VA medical centers. They are also developing a toolkit designed specifically to protect unhoused veterans during extreme heat episodes.
To put this study into a broader scientific context, it aligns with decades of evidence showing that extreme heat is one of the most deadly environmental hazards—more lethal than hurricanes, floods, and tornadoes combined. People with cardiometabolic diseases are already known to be highly sensitive to temperature spikes. Heat can strain the heart, impair blood pressure regulation, worsen dehydration, and exacerbate kidney dysfunction. Even a small rise in outdoor temperature can increase cardiovascular stress, and for older adults or those with chronic illnesses, these effects compound quickly.
Adding to this, urban heat islands can raise neighborhood temperatures by several degrees. Studies have shown that areas with more pavement, fewer trees, and older housing infrastructure stay warmer at night, reducing the body’s ability to cool down. Low-income neighborhoods—more likely to house veterans at risk—are disproportionately affected by this phenomenon. The intersection of health status, medication use, age, housing conditions, and urban design creates a dangerous combination under extreme heat.
This research serves as another reminder that climate change isn’t a distant threat—it’s already reshaping public health. As heat waves become more frequent, protecting vulnerable populations will become a key responsibility for healthcare systems, cities, and policymakers. Veterans, especially those with chronic health conditions and unstable housing, will need targeted interventions to stay safe.
For now, the takeaway for readers is simple: extreme heat can be deadly for individuals with cardiometabolic conditions, and the risks increase when social and environmental disadvantages are layered on top. Awareness, preparedness, and community support will be essential as California and the rest of the world face hotter summers in the years ahead.
Research Paper:
Extreme Heat, Social Factors, and Mortality Among California Veterans With Cardiometabolic Disease (JAMA Network Open)
