As scientists continue to discover evidence linking climate change to a vast array of negative health effects, accumulating findings highlight its potential impact on cardiovascular disease (CVD) and related mortality. In research published in June 2022 in Circulation, the authors noted the increase in extreme heat events due to climate change and aimed to identify associations between extreme heat days in summer months and monthly rates of CV mortality in the United States.1
Extreme heat days were “identified if the maximum heat index was ≥90 °F (32.2 °C) and in the 99th percentile of the maximum heat index in the baseline period (1979-2007) for that day,” as explained in the paper. The study focused on adults aged 20 or older from all 3,108 counties across the contiguous US.
Results demonstrated that extreme heat was linked to an estimated 5,958 additional deaths (95% CI, 1847-10,069) from CVD during summer months from 2008 and 2017. Each additional day of extreme heat per month was associated with a 0.12% (95% CI, 0.04%-0.21%; P =.004) increase in the monthly CV mortality rate.
Subgroup analyses revealed greater relative increases in monthly CV mortality rates among men compared with women (0.20%; 95% CI, 0.07%-0.33%) and among non-Hispanic Black adults compared with non-Hispanic White adults (0.19%; 95% CI, 0.01%-0.37%). There was also a greater absolute increase among older vs younger adults (16.6 [95% CI, 14.6-31.8] additional deaths per 10 million individuals per month).
In a 2019 study, Chen et al analyzed data from the KORA Myocardial Infarction Registry and found that the relative risk (RR) of heat-related myocardial infarction (MI) in 1 German city increased from 0.93 (95% CI, 0.78–1.12) in 1987 to 2000 to 1.14 (95% CI, 1.00–1.29) in 2001 to 2014, with similar trends noted for recurrent and non-ST-segment elevation MI events.2 Patients with diabetes mellitus and hyperlipidemia demonstrated greater vulnerability to the increase in heat-related MI risk compared to other groups.
When it comes to climate change-related extreme heat, clinicians providing care to patients with CVD disease should highlight the importance of avoiding being in extremely hot settings for a prolonged period of time, and they should inform patients that this can impact their health.
These results indicate that “exposure to heat should be considered as an environmental trigger of MI, especially under a warming climate,” the authors wrote.2 “This observation indicates that the health effects of altered temperature exposure are already detectable now and confer an additional burden on vulnerable subgroups of the general population.”
In a 2020 study focused on Kuwait, which experiences some of the highest temperatures on earth, the RR of CV-related death was 3.09 (95% CI, 1.72–5.55) at an extreme temperature (108.9°F) compared to the temperature associated with the lowest mortality risk (94.5°F).3
Researchers have also observed elevated CV risks related to extreme cold weather. In a 2021 study, hospital admission rates for CVD were higher during extreme weather events than on average weather days in a city in southern Brazil. The risk for CV-related hospitalization was especially high during the 7 days following the end of a cold wave, and a greater number of hospitalizations occurred during winter vs summer.4
It has been “hypothesized that the reduced circulatory reserve of older adults amplifies their susceptibility to the myocardial and metabolic demands imposed by physical activity in cold weather conditions and snow,” wrote Chang et al in a review published in Current Cardiology Reports.5
Research based in a large city in China found that CV mortality risk in extremely high temperatures was not significant (P >.05), while extremely low temperatures were linked to greater relative CV mortality risk in certain groups: 6
- Individuals with cerebrovascular disease vs ischemic heart disease (RR, 1.282; 95% CI, 1.020–1.611)
- Males vs females (RR, 1.492; 95% CI, 1.175–1.896)
- Married vs unmarried individuals (RR, 1.590; 95% CI, 1.224–2.064)
- Patients younger than 65 years vs those aged 65 years or older (RR, 1.641; 95% CI, 1.106–2.434)
Similar to the study based in Brazil, the CV effects of cold temperatures persisted for days following the cold weather events.
In findings presented at the European Society of Cardiology Congress 2022, Agewall et al7 observed increased CV risks associated with both cold and hot temperatures, including a 19% increase in CV-related death (RR, 1.19; 95% CI, 1.04-1.36) and a 22% increase in death from ischemic heart disease (RR, 1.22; 95% CI, 1.07-1.38) with a temperature drop from 5°C to -5°C. Among individuals with CVD at baseline, the risk of death from CVD and stroke increased from 25% (RR, 1.25; 95% CI, 1.12-1.39) and 30% (RR, 1.30; 95% CI, 1.10-1.53), respectively, in association with a temperature increase from 15°C to 24°C.
Extreme temperatures interact with other factors linked to climate change, including increasing levels of air pollution, as well as demographic factors such as age, health status, and socioeconomic status, to increase the risk for avoidable CV events.8 For example, Chang et al5 reported that “warmer weather and greater rainfall in certain regions have led to increased airborne pollen and mold spore counts, which have been linked to surges in emergency room visits for myocardial infarctions and strokes, as well as all-cause cardiovascular mortality.”
Based on increasing evidence of the interaction between climate change and CV health, Hadley et al have advocated for the creation of a new field of “climate cardiology” to study and implement opportunities protect CV health and mitigate climate change.9
Cardiology Advisor interviewed the following experts to glean further insights regarding the potential impact of climate change on CV health: Sameed Khatana MD, MPH, senior fellow and assistant professor in the division of cardiovascular medicine at the Perelman School of Medicine at the University of Pennsylvania, and staff cardiologist at the Philadelphia VA Medical Center; and Barrak Alahmad, MD, MPH, PhD, research fellow in the Exposure, Epidemiology and Risk Program in the department of environmental health at the Harvard T.H. Chan School of Public Health in Boston. Both experts are lead authors on 2 of the studies described above.1,3
What does the evidence suggest thus far about the impact of climate change on CV health?
Dr Khatana: Climate change is leading to a myriad of changes in weather patterns including more extreme heat events, floods, droughts, and other natural disasters. As the CV system is central to the body’s regulation of extreme temperatures, extreme heat has been shown in previous studies to be associated with CV mortality. Death from CVD is likely the single largest component of all deaths related to extreme heat.
In our study published in Circulation, my colleagues and I noted that extreme heat was associated with an average of 600 to 700 CV deaths per year among adults living in the contiguous US.1 Individuals with pre-existing CV conditions and those taking certain medications such as β-blockers and diuretics are at a higher risk for adverse health effects due to extreme heat.
Dr Alahmad: Climate change can affect CV health both directly and indirectly. Direct pathways occur through exposure to extreme temperatures and poor air quality, which promote systemic inflammation and a hypercoagulable state and alter thermoregulatory processes.
Indirect pathways include exposure to the by-products of climate change, such as damaged health care infrastructure from extreme weather events, wildfires, or secondary pollutants. We dug deep into these complex relationships in our Nature Reviews paper.10
What can clinicians do to help buffer the impact of climate change on the CV health of their patients?
Dr Khatana: When it comes to climate change-related extreme heat, clinicians providing care to patients with CVD disease should highlight the importance of avoiding being in extremely hot settings for a prolonged period of time, and they should inform patients that this can impact their health.
Patients who do not have access to a cool environment should be advised to seek places with air conditioning such as a cooling center. Patients with mobility disorders and frailty are at a particular high risk of adverse events, so coming up with a plan for what to do in the setting of extreme heat is very important for these patients.
Dr Alahmad: At the population level, the evidence on climate change and CV health is increasing. However, the evidence is still lagging to understand what cardiologists should do from a health care provider point of view. A new study by Kai Chen and colleagues showed that there are some medications that could increase the risk of heat-triggered myocardial infarction.11
What broader measures are needed to address this issue?
Dr Khatana: Beyond clinical care, measures at the local, regional, and national levels are needed to help address climate change in general and extreme heat in particular. Increasing tree cover in communities may mitigate some of the adverse health effects of extreme heat. Policies to ensure that power isn’t cut from peoples’ houses in the setting of an extreme heat event may also play a role.
Local governments should also ensure that they have adequate plans for creating cooling centers that are readily accessible to those who need them. Finally, efforts to limit greenhouse gas emissions at the national and global levels are absolutely necessary to limit the degree to which extreme heat events will increase.
Dr Alahmad: There is no magic stick, no silver bullet. Multilevel interventions from an individual-level to a system-level approach are urgently needed to address this existential problem. Any intervention should involve cross-disciplinary collaboration between physicians, researchers, public health workers, political scientists, legislators, and national leaders to mitigate the effects of climate change.
What are some of the key remaining topics warranting further research in this area?
Dr Khatana: Identifying which CV patients and which particular medications increase the risk for adverse health events due to extreme heat is important. Additionally, studying whether interventions such urban greening can lessen the impact of extreme heat on CV health is also needed.
Dr Alahmad: We need to understand which CV diseases are most sensitive to climate change-related exposures. We need interventional studies to mitigate climate risks on patients with pre-existing CV conditions. We also need to identify the populations that are most vulnerable to these risks.
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