Extreme heat could elevate cardiovascular mortality for US residents by midcentury

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In a recently published study, Dr circulation, Researchers estimate the changing burden of severe heat-related cardiovascular deaths in the United States.

Study: Projected changes in mean excess cardiovascular mortality associated with extreme heat in the contiguous United States by midcentury (2036–2065). Image credit: DStockography / Shutterstock.com

How does extreme heat affect health?

Extreme heat events in the United States are expected to become more frequent and severe due to global climate change. Heat exposure can increase heart strain, cytokine secretion, and thrombosis, thereby increasing the risk of myocardial infarction and stroke.

Individuals suffering from cardiovascular disease and risk factors are more vulnerable to the negative health effects of severe heat. The effect of this increase in extreme heat on cardiovascular health is unknown; Therefore, it is important to analyze the combination of demographic and environmental changes to accurately estimate the impact of extreme heat events on US adults in the coming decades.

About the study

Between 2008 and 2019, researchers obtained data on cardiovascular deaths among adults and the frequency of extreme heat days in 3,018 contiguous US counties. Data were collected on county-level projected numbers and population for two scenarios between 2036 and 2065 mid-century. These projections were based on Representative Concentration Pathways (RCPs) trajectories modeling greenhouse gas emissions and shared socioeconomic pathways. (SSPs) Modeling future socio-economic conditions and population projections.

The scenarios included a “middle-of-the-road” socio-economic situation and elevated levels of greenhouse gas (SSP2-4.5) emissions and demographic projections based on fossil fuel development and significant growth in the economy. In Greenhouse Gas Emissions (SSP5-8.5). Poisson fixed-effects models estimate the association between high heat and cardiovascular disease-related mortality.

The number of severe heat-related cardiovascular deaths was predicted using model assumptions. An expression of concern was extreme heat, which refers to temperatures much higher than normal for a particular location.

The primary study results were average annual predicted excess cardiovascular mortality rates in the contiguous United States using the SSP2-4.5 and SSP5-8.5 scenarios for the mid-century time frame. Excess cardiovascular mortality was assessed by age, sex, race, and ethnic subgroups.

The Union of Concerned Scientists provides data to predict the average number of extreme heat days per year by mid-century in each U.S. county. Secondary evaluations employed alternative definitions of heat index (HIs) of 100 °F (37.8 °C) and 105 °F (40.6 °C) to estimate excess mortality from cardiovascular disease in sex, age, race, ethnicity, subgroups. and housing type.

International Classification of Diseases, 10th Revision (ICD-10) codes were used along with National Centers for Health Statistics data to determine cardiovascular mortality. Age, sex, race, and ethnicity information of deceased individuals was obtained from their death certificates.

Study results

Between 2008 and 2019, extreme heat was associated with an additional 1,651 cardiovascular deaths each year. Under SSP2-4.5, extreme heat was estimated to cause 4,320 excess deaths per year, reflecting a 162% increase, over mid-century and 5,491 annual excess deaths, or a 233% increase over the SSP5-8.5 scenario.

In the SSP2-4.5 scenario, mortality was predicted to increase fourfold for older persons aged 65 years and older compared to younger persons aged 20 to 64 years. Estimated changes in mortality were not significantly different between race and ethnicity or between men and women.

Between 2008 and 2019, more than three million people died in the United States from cardiovascular disease between May and September. Half of the deaths were women, 12% among blacks of non-Hispanic ethnicity, 85% among whites of non-Hispanic ethnicity, 3% among persons of other races but non-Hispanic ethnicity, 6% among Hispanics of any ethnic group, and 0.30% among persons with unknown race and ethnicity.

During this time, the average monthly cardiovascular death rate was 26 deaths per 100,000 persons. Between 2008 and 2019, the county averaged 54 days per year with a maximum HI value of 90 °F. Average counts of extreme heat days per year were predicted to increase to 71 and 80 on the representative concentration pathway. 4.50 and 8.50 respectively.

Under the SSP2 and SSP5 scenarios, the average number of adults in US counties was expected to exceed 300 million under SPP2 and 354 million under SSP5, up from 233 million in the mid-century period.

The median population of US adults was expected to decrease from 19,524 to 18,252 and 20,747 under the SSP2 and SSP5 scenarios, respectively. The expected change in the proportion of adults between now and mid-century was 5% under SPP2 and 9% under SPP5. The proportion of county residents age 65 was expected to increase from 23% currently to 31% under both scenarios.


Projected warming is expected to be associated with a much higher burden of excess cardiovascular mortality in the contiguous United States by midcentury. This increase in mortality is likely due to the combined effects of an increase in extreme hot days, an aging population, and continued migration to warmer places.

A greater number of extreme heat days may exacerbate pre-existing disparities in cardiovascular health within the population, particularly between black and white individuals of non-Hispanic ethnicity. Thus, population health and infrastructure measures are urgently needed to help populations adapt to the expected increase in extreme heat and mitigate its negative health impacts.

Journal Reference:

  • Khatana, S.A.M., Eberly, L.A., Nathan, A.S., and Groeneveld, P.W. (2023). Projected changes in mean excess cardiovascular mortality associated with extreme heat in the contiguous United States by midcentury (2036–2065). circulation. doi:10.1161/CIRCULATIONAHA.123.066017

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