Extreme heat set to double, or even triple, heart-related deaths by mid-century, study warns

30 October 2023

Cardiovascular deaths in extreme heat in the United States may more than double by the middle of this century. Without greenhouse gas emissions, that number could even drop threefold, according to new research published today in the American Heart Association’s flagship journal.circulation.

Study: Projected Changes in Mean Excess Cardiovascular Mortality Associated with Extreme Heat in the Contiguous United States by Mid-Century (2036-2065). Image credit: Created with assistance from DALL·E 3

“Climate change and its many manifestations will play an increasingly important role in the health of communities around the world in the coming decades,” said study lead author Samid Khatana, MD, MPH, assistant professor of medicine at the University of Pennsylvania and an activist. Cardiologists at the Philadelphia Veterans Affairs Medical Center, both in Philadelphia. “Climate change is also a health equity issue because it will disproportionately affect certain individuals and populations and may exacerbate existing health disparities in the United States.”

How much and how fast greenhouse gas emissions increase in the coming decades will determine the health impacts of extreme heat. More aggressive policies to reduce greenhouse gas emissions are likely to reduce the number of people who may experience adverse health effects from extreme heat, according to Khatana.

Previously, the authors examined county-by-county data in the continental United States and demonstrated a link between a significantly greater number of extreme heat days and an increase in cardiovascular mortality between 2008-2017. This data has served as a benchmark for analysis in this new study. The researchers used models of future greenhouse gas emissions and the future socioeconomic and demographic makeup of the US population to estimate the potential impact of extreme heat on cardiovascular mortality 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 versus if no extreme heat had occurred. If the estimated number of heat days occurred.

The analysis found:

• Between 2008 and 2019, extreme heat was associated with 1,651 excess cardiovascular deaths annually.
• 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 than the 2008-2019 baseline by mid-century.
• However, if those greenhouse gas emission reduction policies are not implemented, excess cardiovascular deaths due to extreme heat are projected to increase by 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 experience a 2.9 to 3.5 times greater increase in cardiovascular deaths due to extreme heat than adults aged 20-64.
• Non-Hispanic white adults are estimated to be 3.8 to 4.6 times more likely to have cardiovascular deaths due to extreme heat than non-Hispanic white adults, depending on the degree to which greenhouse policies are implemented.
• Estimated increases in heat-related deaths were not significantly different among adults in other racial or ethnic groups or between men and women.

“The magnitude of the percentage increase was surprising. This increase is not only attributable to the known association between cardiovascular deaths and extreme heat, but is also influenced by the aging of the population and the proportional increase in the number of people from other races and/or ethnicities in the United States,” Khatana said.

Both medical and environmental factors may influence the greater impact of extreme heat on people in this population group, he said. Neighborhood inequality and environmental factors are also important factors to consider.

“Previous research has suggested that black residents may have less access to air conditioning; less tree cover; and higher levels of the ‘urban heat island effect’ — where temperatures rise more in built-up areas than in surrounding less-developed areas,” Khatana said. said. “Living conditions may also play a role in terms of social isolation, which is experienced by some older adults and has previously been associated with a higher likelihood of death from extreme heat.”

Unfortunately, that’s not surprising, according to American Heart Association volunteer Robert Brooke, MD, FAHA, who has co-authored several association articles. Scientific statement 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 they decrease,” said Brooke, professor of medicine and executive director of cardiovascular prevention at Wayne State University School of Medicine in Detroit. “Furthermore, most pollutants persist in the atmosphere for many years, and as such, the long-term trend is a significant increase in the frequency of extreme heat events despite near-term activity.

“In conjunction with the growth of a more susceptible and vulnerable population -; older adults and people moving to warmer places -; heat-related cardiovascular disease deaths are expected to increase in the coming decades. Nevertheless, studies show that the level of adverse cardiovascular disease “is due to climate change. By taking earlier steps to reduce the greenhouse gas emissions that drive them, the impact of disease can be mitigated to some extent.”

While the estimates may seem alarming, they are likely conservative, Brooke noted.

“The estimates in this study focus on cardiovascular disease mortality, and therefore, they represent conservative estimates of adverse effects on cardiovascular health due to extreme heat,” he said. “Nonfatal heart attack, stroke, and heart failure hospitalizations outnumber fatal events and are more likely to be associated with extreme heat days. The full extent of the public health threat, even just from cardiovascular deaths, is probably much more study than it presents.”

The estimates raise the question of whether infrastructure interventions, such as increasing neighborhood tree cover, could improve the number of people affected by extreme heat in the United States. However, research in the United States is lacking.

Brooke also notes the role of pollution with excess heat: “Fine particulate matter air pollution (PM_2.5) causes more than 6 million deaths each year. This study adds to the evidence that the full extent of the harmful effects caused by air pollutants extends beyond the PM._2.5. By significantly increasing days of extreme heat, greenhouse air pollutants pose a further threat to our well-being.”

Study Details and Background:

The researchers compared excess cardiovascular deaths due to extreme heat in two scenarios used by the Intergovernmental Panel on Climate Change, an international organization that assesses the science of climate change caused by human activity. The situation was:

• Successful implementation of currently proposed, moderate emissions reduction policies to reduce greenhouse gas emissions; or,
• No significant emission reduction efforts and greenhouse gas emissions have continued to increase at the same rate for the past two decades.
• As a baseline, the researchers used county-by-county records from 2008-2019 for any primary cause of cardiovascular conditions during the summer months (including heart attack and stroke) and related data such as age, sex, race, and ethnicity of each person who died and the number of days of extreme heat. Number (maximum heat index 90 days^oF or higher) in the month of death. The heat index takes into account both heat and humidity because it reflects how the human body experiences high temperatures, as high humidity interferes with the body’s ability to release heat through sweat.

These results, from data from the continental United States, may not apply to people living in the United States or other regions of the world The study is also limited by using two plausible estimates of extreme heat and population change, and actual changes in the United States may be different.

Co-authors and their publications are listed in the manuscript. The American Heart Association and the National Heart, Lung, and Blood Institute, a division of the National Institutes of Health, funded the study.