How does heat affect cardiovascular, kidney, and mental health?

How does heat actually damage your heart and blood vessels?

Heat forces your heart to work harder. To cool your body, blood vessels near the skin widen (vasodilation), and your heart pumps faster to move blood to the surface. This extra strain can trigger heart attacks, strokes, and dangerous heart rhythms, especially in people with existing conditions. A massive 2022 meta-analysis of 266 studies found that each 1°C increase in temperature raises the risk of dying from cardiovascular disease by 2.1% [2]. That may sound small, but it translates to thousands of extra deaths during heatwaves. The same study showed that heatwaves themselves increase cardiovascular death risk by about 17%, and the risk climbs with heatwave intensity—low-intensity heatwaves raised risk by 6.7%, while high-intensity ones raised it by nearly 19% [2]. The most vulnerable groups are women, people over 65, those in tropical climates, and people in lower-middle-income countries [2].

There's also a two-way link between mental health and heart health. A 2023 study of nearly 600,000 young US adults found that people with depression had more than double the odds of having cardiovascular disease (like heart attack or stroke) compared to those without depression, even after accounting for other risk factors like smoking and obesity [4]. The more days of poor mental health someone reported, the higher their heart disease risk—a clear dose-response relationship [4]. This means that heat's effect on mental health can indirectly worsen heart health, creating a dangerous cycle.

What about the kidneys—are they affected by heat too?

While the provided studies focus on heart and mental health, the kidney connection is well-established in other research. Heat causes dehydration and reduces blood flow to the kidneys, which can lead to acute kidney injury, especially in outdoor workers and older adults. The cardiovascular meta-analysis [2] notes that heat increases hospitalizations for heart conditions, and since heart and kidney function are tightly linked (cardiorenal syndrome), any strain on the heart also stresses the kidneys. The mental health studies [1][3][5] don't directly measure kidney outcomes, but the same populations at risk for heat-related heart problems—older adults, those with chronic disease—are also at high risk for kidney damage.

Can heat really cause mental health emergencies?

Yes, and the evidence is surprisingly strong. A 2026 meta-analysis of 28 studies covering over 1.1 million children and adolescents found that high temperatures were linked to a 13% higher risk of hospital visits for any mental health disorder, an 18% higher risk for depression, and a 14% higher risk for schizophrenia, compared to cooler temperatures [1]. Each 1°C rise was also associated with a 1% increase in suicide risk [1]. A separate 2026 study of over 719,000 hospital admissions in Australia found that on very hot days (99th percentile temperature), the risk of being admitted for a mental health condition was roughly 2 to 3 times higher than on the mildest-temperature days, depending on the season [3]. The effects were strongest for substance use disorders, depression, anxiety, and self-harm [3]. Notably, the risk was higher in cold-season hot days, suggesting that unexpected heat may be more disruptive than predictable summer heat [3].

Heat doesn't just affect young people. A 2025 study of older Chinese adults found that cumulative heat exposure over many days was linked to worse mental health, and that part of this effect was explained by changes in social networks—people's peripheral social ties shrank, though their core networks expanded slightly [5]. This suggests heat may isolate people socially, which itself harms mental health. The study also projected that under high-emission climate scenarios, heat-attributable mental health admissions could rise by over 20% by the 2090s [3].

About These Sources

This answer is built on 5 peer-reviewed studies — published from 2022 to 2026, 3 from 2024 or later, 5 in Q1 journals, collectively cited 638 times — selected as the most relevant from 5 studies that passed quality screening, drawn from 48 papers retrieved from a database of over 500 million.

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