Extreme heat projected to increase cardiovascular deaths
NIH-funded study predicts older and Black adults will suffer most
For immediate release on Oct. 30, 2023
Cardiovascular-related deaths due to extreme heat are expected to increase between 2036 and 2065 in the United States, according to a study supported by the National Institutes of Health. The researchers, whose work is published in Circulation, predict that adults ages 65 and older and Black adults will likely be disproportionately affected.
While extreme heat currently accounts for less than 1% of cardiovascular-related deaths, the modeling analysis predicted this will change because of a projected rise in summer days that feel at least 90 degrees. This heat index, which factors in what the temperature feels like with humidity, measures extreme temperature. Older adults and Black adults will be most vulnerable because many have underlying medical conditions or face socioeconomic barriers that can influence their health – such as not having air conditioning or living in locations that can absorb and trap heat, known as “heat islands.”
“The health burdens from extreme heat will continue to grow within the next several decades,” said Sameed A. Khatana, M.D., M.P.H., a study author, cardiologist, and assistant professor of medicine at the University of Pennsylvania, Philadelphia. “Due to the unequal impact of extreme heat on different populations, this is also a matter of health equity and could exacerbate health disparities that already exist.”
To generate these predictions, researchers evaluated county-level data from the contiguous 48 states between May and September of 2008–2019. More than 12 million deaths related to cardiovascular disease occurred during that time. Using environmental modeling estimates, they also found that the heat index rose to at least 90 degrees about 54 times each summer. Researchers linked the extreme temperatures that occurred during each summer period to a national average of 1,651 annual cardiovascular deaths. Some areas, such as the South and Southwest, were affected more than others, such as the Northwest and Northeast.
Using modeling analyses to forecast environmental and population changes, the researchers looked to 2036–2065 and estimated that each summer, about 71 to 80 days will feel 90 degrees or hotter. Based on these changes, they predicted the number of annual heat-related cardiovascular deaths will increase 2.6 times for the general population — from 1,651 to 4,320. This estimate is based on greenhouse gas emissions, which trap the sun’s heat, being kept to a minimum. If emissions rise significantly, deaths could more than triple, to 5,491.
For older adults and Black adults, the projections were more pronounced. Among those ages 65 and older, deaths could almost triple, increasing from 1,340 to 3,842 if greenhouse gas emissions remain steady — or to 4,894 if they don’t. Among Black adults, deaths could more than triple, rising from 325 to 1,512 or 2,063.
In comparing current and future populations, the researchers accounted for multiple factors, including age, underlying health conditions, and where a person lived.
Most people adapt to extreme heat, as the body finds ways to cool itself, such as through perspiration. However, people with underlying health conditions, including diabetes and heart disease, can have different responses and face increased risks for having a heart attack, irregular heart rhythm, or stroke.
“The number of cardiovascular events due to heat affects a small proportion of adults, but this research shows how important it is for those with underlying risks to take extra steps to avoid extreme temperatures,” said Lawrence J. Fine, M.D., a senior advisor in the clinical applications and prevention branch, in the Division of Cardiovascular Sciences at the National Heart, Lung, and Blood Institute (NHLBI), part of NIH.
The authors described cooling approaches that some cities are using – planting trees for shade, adding cooling centers with air conditioning, and using heat-reflective materials to pave streets or paint roofs. However, more research is necessary to understand how these approaches may impact population health.
“In addition to thinking about the impact of extreme temperatures in the U.S., this type of modeling forecast also foreshadows the impact that extreme heat could have throughout the world, especially in regions with warmer climates and that are disproportionately affected by health disparities,” said Flora N. Katz, Ph.D., director of the Division of International Training and Research at the NIH Fogarty International Center.
The research was partially supported by NHLBI grant K23 HL153772.
Study: Khatana SE, Eberly LA, Nathan AS, et al. Projected change in the burden of excess cardiovascular deaths associated with extreme heat by mid-century (2036-2065) in the contiguous United States. Circulation. 2023; doi: 10.1161/CIRCULATIONAHA.123.066017.
To learn about the NIH Climate Change and Health Initiative, visit https://www.nih.gov/climateandhealth.
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JOURNAL
Circulation
ARTICLE TITLE
Projected change in the burden of excess cardiovascular deaths associated with extreme heat by mid-century (2036-2065) in the contiguous United States
ARTICLE PUBLICATION DATE
30-Oct-2023
Heat-related cardiovascular deaths in the U.S. may more than double within decades
In nationwide projections, elderly and Black adults are most at risk for cardiovascular death due to extreme heat, finds a new study in journal, Circulation
Peer-Reviewed PublicationResearch Highlights:
- Cardiovascular deaths from extreme heat in the United States are projected to increase by 162% by the middle of the century, based on a hypothetical scenario where currently proposed U.S. policies to reduce greenhouse gas emissions have been successfully implemented.
- A more dire scenario forecasts cardiovascular deaths from extreme heat could increase by 233% in the next 13-47 years if there are only minimal efforts to reduce emissions.
- The percentage increase in deaths will be greater among elderly people and non-Hispanic Black adults in either scenario.
DALLAS, Oct. 30, 2023 — Cardiovascular deaths from extreme heat in the U.S. may more than double by the middle of the century. Without reductions in greenhouse gas emissions, that number could even triple, according to new research published today in the American Heart Association’s flagship journal Circulation.
“Climate change and its many manifestations will play an increasingly important role on the health of communities around the world in the coming decades, “ said lead study author Sameed Khatana, M.D., M.P.H., assistant professor of medicine at the University of Pennsylvania and a staff cardiologist at the Philadelphia Veterans Affairs Medical Center, both in Philadelphia. “Climate change is also a health equity issue as it will impact certain individuals and populations to a disproportionate degree and may exacerbate preexisting health disparities in the U.S.”
How much and how quickly greenhouse gas emissions increase in the next decades will determine the health impacts of extreme heat. More aggressive policies to reduce greenhouse gas emissions have the potential to reduce the number of people who may experience the adverse health effects of extreme heat, according to Khatana.
Previously, the authors examined county-by-county data in the continental U.S. to demonstrate a link between a greater number of extreme heat days and an increase in cardiovascular deaths between 2008-2017. This data served as a benchmark for the analysis in this new study. Researchers used models for future greenhouse gas emissions and future socioeconomic and demographic makeup of the U.S. population to estimate the possible impact of extreme heat on cardiovascular deaths in the middle years of the current century (2036-2065). They estimated the excess number of cardiovascular deaths associated with extreme heat by comparing the predicted number of deaths for each county if no extreme heat occurred vs. if the projected number of heat days occurred.
The analysis found:
- Between 2008 and 2019, extreme heat was associated with 1,651 excess cardiovascular deaths per year.
- Even if currently proposed reductions in greenhouse gas emissions are fully implemented, excess cardiovascular deaths due to extreme heat are projected to be 162% higher in the middle of this century compared to the 2008-2019 baseline.
- However, if those greenhouse gas emissions reduction policies are not implemented, excess cardiovascular deaths due to extreme heat are projected to increase 233% in the coming decades.
- Depending on how aggressively policies to reduce greenhouse gas emissions are implemented, adults aged 65 and older are projected to have a 2.9 to 3.5 times greater increase in cardiovascular death due to extreme heat in comparison to adults ages 20-64.
- Non-Hispanic Black adults are projected to have a 3.8 to 4.6 times greater increase in cardiovascular death due to extreme heat compared with non-Hispanic white adults, depending on the degree to which greenhouse policies are implemented.
- Projected increases in deaths due to extreme heat were not significantly different among adults in other racial or ethnic groups, or between men and women.
“The magnitude of the percent increase was surprising. This increase accounts for not only the known association between cardiovascular deaths and extreme heat, but it is also impacted by the population getting older and the proportionate increases in the number of people from other races and/or ethnicities in the U.S.,” Khatana said.
Both medical and environmental factors may influence the greater impact of extreme heat for people in these population groups, he said. Disparities in neighborhood and environmental factors are crucial factors to also consider.
“Previous studies have suggested Black residents may have less access to air conditioning; less tree cover; and a higher degree of the ‘urban heat island effect’ — built-up areas having a greater increase in temperature than surrounding less-developed areas,” Khatana said. “Living conditions may also have a role in terms of social isolation, which is experienced by some older adults and has previously been linked with a higher probability of death from extreme heat.”
The findings are unfortunately, not surprising, according to American Heart Association volunteer Robert Brook, M.D., FAHA, who has co-authored several Association scientific statements on air pollution and was not involved in this study.
“Even under the more optimistic moderate scenario of this study, greenhouse gas emissions will increase for some time before tapering down,” said Brook, professor of medicine and executive director of cardiovascular prevention at Wayne State University School of Medicine in Detroit. “Moreover, most of the pollutants persist in the atmosphere for numerous years, and as such, the long-term trend is for significant increases in the frequency of extreme heat events despite near-term actions.
“In conjunction with the growth of more susceptible and vulnerable populations — aging adults and people relocating to warmer locations — heat-related cardiovascular disease deaths are expected to increase over the coming decades. Nevertheless, the study shows that the magnitude of adverse cardiovascular disease effects may be somewhat mitigated by taking earlier action to reduce greenhouse gas emissions that drive climate change.”
While the projections may appear alarming, they are likely conservative, Brook noted.
“The projections of this study focus on cardiovascular disease deaths, and, therefore, they represent conservative estimations of the adverse effects on cardiovascular health due to extreme heat,” he said. “Nonfatal heart attacks, strokes and heart failure hospitalizations outnumber fatal events and are also highly likely to be linked with extreme heat days. The full extent of the public health threat, even just due to cardiovascular death, is likely much greater than presented in this study. “
The projections raise the question of whether infrastructure interventions, such as increasing tree cover in neighborhoods, may lead to improvements in the number of people affected by extreme heat in the U.S. Some research results from Europe suggest that this may be the case, however, studies in the U.S. are lacking.
Brook also noted the role of pollution with excessive heat: “Fine particulate matter air pollution (PM2.5) causes more than 6 million deaths per year. This study adds to the evidence that the full extent of the harmful effects posed by air pollutants extends beyond PM2.5. By substantially increasing extreme heat days, greenhouse air pollutants pose yet further threats to our well-being.”
Study details and background:
- The researchers compared excess cardiovascular deaths due to extreme heat under two scenarios used by the Intergovernmental Panel on Climate Change, an international body that assesses the science related to climate change caused by human activities. The scenarios were:
- successful implementation of currently proposed, moderate emission reduction policies so there are lower increases in greenhouse gas emissions; or
- no significant emission reduction efforts and greenhouse gas emissions continue to increase at the same rate they have over the last two decades.
- As a baseline, the researchers used county-by-county records from 2008-2019 for deaths during summer months with a primary cause of any cardiovascular condition (including heart attack and stroke), and related data such as the age, sex, race and ethnicity of each person who died and the number of extreme heat days (days with a maximum heat index of 90oF or higher) during the month of the death. The heat index considers both heat and humidity because that reflects how the human body experiences high temperatures, with high humidity interfering with the body’s ability to release heat by sweating.
These results, from data in the continental U.S., may not apply to people living in other regions of the U.S. or the world. The study is also limited by employing two plausible projections of extreme heat and population change, and it is possible that the actual changes in the U.S. may be different.
Co-authors and their disclosures are listed in the manuscript. The study was funded by the American Heart Association and the National Heart, Lung, and Blood Institute, a division of the National Institutes of Health.
Studies published in the American Heart Association’s scientific journals are peer-reviewed. The statements and conclusions in each manuscript are solely those of the study authors and do not necessarily reflect the Association’s policy or position. The Association makes no representation or guarantee as to their accuracy or reliability. The Association receives funding primarily from individuals; foundations and corporations (including pharmaceutical, device manufacturers and other companies) also make donations and fund specific Association programs and events. The Association has strict policies to prevent these relationships from influencing the science content. Revenues from pharmaceutical and biotech companies, device manufacturers and health insurance providers and the Association’s overall financial information are available here.
Additional Resources:
- Multimedia is available on the right column of release link https://newsroom.heart.org/news/heat-related-cardiovascular-deaths-in-the-u-s-may-more-than-double-within-decades?preview=880e45b4ec096375a8c2aff458d27b76
- After Oct. 30, view the manuscript online.
- AHA news release: Risk of fatal heart attack may double in heat wave & high fine particulate pollution days (July 2023)
- AHA news release: Particulate air pollution a growing risk for premature CVD death and disability worldwide (Aug. 2023)
- AHA news release: Extremely hot and cold days linked to cardiovascular deaths (Dec. 2022)
- AHA news release: Extreme, high temperatures may double or triple heart-related deaths (March 2020)
- Follow AHA/ASA news on X (formerly known as Twitter) @HeartNews
- Follow news from AHA’s flagship journal Circulation @CircAHA
About the American Heart Association
The American Heart Association is a relentless force for a world of longer, healthier lives. We are dedicated to ensuring equitable health in all communities. Through collaboration with numerous organizations, and powered by millions of volunteers, we fund innovative research, advocate for the public’s health and share lifesaving resources. The Dallas-based organization has been a leading source of health information for nearly a century. Connect with us on heart.org, Facebook, X or by calling 1-800-AHA-USA1.
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JOURNAL
Circulation
ARTICLE TITLE
Projected Change in the Burden of Excess Cardiovascular Deaths Associated With Extreme Heat by Midcentury (2036–2065) in the Contiguous United States
Penn research projects increase in US cardiovascular deaths due to extreme heat
Study indicates that older adults and Black adults are at greater risk of excess deaths
PHILADELPHIA— The number of heat related cardiovascular deaths in the United States will increase over the next four decades, according to a new analysis from the Perelman School of Medicine at the University of Pennsylvania. Extreme heat can impact heart health in many ways, including increased heart rate, changes in blood pressure, and increased inflammation. Left untreated, these issues can be deadly. The findings, published today in Circulation, also indicate that older adults and Black adults will experience greater increases in excess cardiovascular deaths due to extreme heat.
“As global temperatures rise, analyzing how demographic and environmental trends are connected is necessary for accurate forecasts of how extreme heat events will impact the cardiovascular health of U.S. adults in the coming decades,” said Sameed Khatana, MD, MPH, an assistant professor of Cardiovascular Medicine at Penn and senior author of the study.
According to the analysis, the number of cardiovascular deaths associated with extreme heat among adults living in the United States is projected to have a statistically significant increase from the current period (2008-2019) to the mid-century period (2036-2065).
To reach this conclusion, researchers evaluated the number of cardiovascular deaths that were associated with extreme heat from 2008-2019. In that time period, there were an average of 54 days each summer when the heat index rose to or above 90 degrees and a total of 1,651 related cardiovascular deaths annually. Researchers then combined this estimate with the projected number of extreme heat days, as well as population levels in the middle of the century. As a result of more regularly recurring hot temperatures and demographic changes, they project between 4,320 to 5,491 deaths annually come the middle of the 21st century.
Furthermore, they analyzed this impact on subgroups of populations, including older adults and Black adults. The researchers found that Black adults may experience even greater increases of cardiovascular related deaths due to heat exposure, with a more than 500 percent increase in the coming decade compared to current deaths from cardiovascular related complications. This could be due to the increased risks Black adults have for cardiovascular disease, which can be tied to factors such as social determinants of health (like neighborhood poverty level) and clinical factors (such as blood pressure). Additionally, previous studies have shown that neighborhoods with a higher proportion of non-white residents have lower air conditioning access and less tree canopy cover which increases heat exposure to the residents of these neighborhoods.
“This is a health equity issue and without steps to mitigate its impacts, extreme heat may widen the pre-existing cardiovascular health disparities that already exist between communities in the United States,” said Khatana.
Additionally, people with underlying conditions such as diabetes and heart disease are at a greater risk when temperatures rise. Irregular heartbeat, heart attack, or stroke can occur as the body tries to cool itself down.
The authors recommend infrastructure investment in high-risk communities to help mitigate the impacts of climate change. For example, increasing tree canopy cover and developing heat action plans—which ensure vulnerable populations have ways to cool down during instances of increasing temperatures—are all ways to help lower the number of cardiovascular deaths related to extreme heat.
The research was partially supported by grants from the American Heart Association (20CDA35320251) and National Heart, Lung, and Blood Institute (K23 HL153772).
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Penn Medicine is one of the world’s leading academic medical centers, dedicated to the related missions of medical education, biomedical research, excellence in patient care, and community service. The organization consists of the University of Pennsylvania Health System and Penn’s Raymond and Ruth Perelman School of Medicine, founded in 1765 as the nation’s first medical school.
The Perelman School of Medicine is consistently among the nation's top recipients of funding from the National Institutes of Health, with $550 million awarded in the 2022 fiscal year. Home to a proud history of “firsts” in medicine, Penn Medicine teams have pioneered discoveries and innovations that have shaped modern medicine, including recent breakthroughs such as CAR T cell therapy for cancer and the mRNA technology used in COVID-19 vaccines.
The University of Pennsylvania Health System’s patient care facilities stretch from the Susquehanna River in Pennsylvania to the New Jersey shore. These include the Hospital of the University of Pennsylvania, Penn Presbyterian Medical Center, Chester County Hospital, Lancaster General Health, Penn Medicine Princeton Health, and Pennsylvania Hospital—the nation’s first hospital, founded in 1751. Additional facilities and enterprises include Good Shepherd Penn Partners, Penn Medicine at Home, Lancaster Behavioral Health Hospital, and Princeton House Behavioral Health, among others.
Penn Medicine is an $11.1 billion enterprise powered by more than 49,000 talented faculty and staff.
JOURNAL
Circulation
ARTICLE PUBLICATION DATE
30-Oct-2023
