Climate change is no longer a distant threat for future generations; the impact of global warming, extreme weather, and other climate impacts millions around the world today. Almost two centuries of fossil fuel combustion steadily increased atmospheric concentration of greenhouse gases—such as carbon dioxide and methane—resulting in substantial global warming. Since 2001, the planet saw 19 of the 20 warmest years on record.¹ Such high temperatures lead to longer and more intense wildfire seasons which, beyond creating local destruction, can lead to smoke plumes affecting air quality and health hundreds of miles away from the source.²

Exposure to extreme temperatures as well as inhaled particulate matter from manmade sources and from wildfire smoke are associated with increased morbidity and mortality from cardiovascular (CV) disease.^3-5 As a considerable number of athletes spend a disproportionate amount of time outside exerting their bodies and CV systems to the limit, they may be at greater risk of these effects. Given the risk of these increasingly common extreme weather events on the CV and pulmonary systems, climate change is already disrupting the sporting world. Numerous indoor and outdoor competitions were cancelled due to the 2017 Northern California wildfires and unprecedented high temperatures led to the cancellation of the 2023 Twin Cities marathon.

The Athlete's Heart Under Environmental Stress

The effects of extreme heat and air pollution are particularly relevant to athletes. While the benefits of exercise on the CV system are well understood, the changing environment in which exercise is performed adds important nuance to medical considerations.

Extreme heat impacts multiple areas of cardiac physiology during exercise. During heat exposure, there is increased blood flow to the skin to cool the body and increased sympathetic activity. These adaptive effects that prevent hyperthermia are thought to be associated with hemoconcentration, hypercoagulability, and electrolyte abnormalities.⁶ Exercise compounds these effects by promoting additional peripheral vasodilation and sympathetic activation, as well as increased cardiac work and output. Patients with underlying CV conditions may be at increased risk of adverse events from these additive physiologic responses in the setting of extreme heat exposure. Hyperthermia related decreases in intravascular volume may exacerbate myocardial supply-demand mismatch, especially in patients with underlying coronary artery disease (CAD). Increased local inflammation as well as hypercoagulability may predispose at-risk individuals to arterial plaque rupture and myocardial infarction (MI).⁷ In patients with chronic heart failure (HF), there is a lack of appropriate increased skin blood flow during heat exposure, which may predispose them to heat related illnesses such as heat stroke.⁶ In addition, commonly prescribed CV medications may modify the risk of MI in those exposed to extreme heat.⁸ Thus, exercise performance as well as management of common CV diseases are adversely impacted by extreme heat exposure.

Air pollution released from industrial processes and wildfires should also be of particular concern to the athlete. During exercise, pulmonary minute ventilation increases which, along with increased airflow velocity, leads to pollutants travelling in greater numbers deeper into the respiratory tract.⁹ This increased pollutant exposure has a twofold effect on athletes. First, exercising in even good-to-moderate air pollution conditions has been shown to decrease peak athletic performance. In a retrospective review of elite runners, a 12.8 second increase in 5-km race times was observed after 21 days of PM_2.5 exposure (AQI 20 vs 43).⁹ In competitive National Collegiate Athletic Association Division-1 championships, a 12 second increase could be the difference between 1st and 6th place.⁹ Second, short- and long-term air pollution exposures are associated with faster development of arterial atherosclerosis and increased major adverse cardiac events such as ischemic heart disease mortality and risk of acute MI.^5,10 Furthermore, ground-level ozone, a pollutant formed from the reaction of nitrogen with volatile organic compounds (such as those released from cars and factories) increases in concentration on hot days. Therefore, athletes training outdoors, especially in the warmer summer months, may be adversely affected by even modest levels of air pollutants.

The Role of the Cardiologist

Cardiologists have a crucial role to play in counseling both recreational and elite athletes for training and sports participation. Patient education on the CV effects of climate change is of special consequence to cardiologists who practice in highly polluted urban areas or in areas that are increasingly affected by wildfires.

For recreational athletes, cardiologists should discuss adequate hydration and advise that patients avoid exercising in moderate or worse air quality based on the air quality index. This advice is particularly important for patients with underlying CAD or HF, given the potentially exacerbated risk of adverse effects with climate change. For example, this may involve counseling athletes to exercise predominantly in the mornings when temperatures are cooler and ozone concentrations are lower.

For elite athletes who push themselves to their physiologic limit, pre-participation evaluations should include an assessment of environmental exposures. When evaluating athletes with preexisting CV disease and/or those with high levels of environmental exposure, future research on customizing stress testing and pre-participation screening is needed to account for environmental stressors in minimizing CV risk.

Future Directions

Exposures to climate change related stressors will become more frequent in the upcoming decades and will have a significant impact on CV morbidity and mortality. All athletes—especially those with preexisting CV conditions—will be at increased risk of a CV event during strenuous exercise when exposed to extreme heat and air pollutants. Given the dearth of studies focusing on the impact of climate change on the athletic heart, more research is needed to better understand the risk in this population. Further research will enable cardiologists to better inform pre-participation evaluation as well as provide counsel for recreational and elite athletic populations. Adaptation strategies such as moving the time and location of athletic competitions are already underway, but organized strategic planning to protect athletes during all stages of competition are needed. As the fields of Sports Cardiology and Climate Medicine continue to grow, we have a unique opportunity to educate and advocate for climate change mitigation and adaptation strategies to reduce CV risk among exposed athletes.

References

1. Climate Change: Vital Signs of the Planet (NASA Global Climate Change website). 2023. Available at: https://climate.nasa.gov/vital-signs/global-temperature/. Accessed 11/20/23.
2. Chen G, Guo Y, Yue X, et al. Mortality risk attributable to wildfire-related PM2·5 pollution: a global time series study in 749 locations. Lancet Planet Health 2021;5:e579-e587.
3. Alahmad B, Khraishah H, Royé D, et al. Associations between extreme temperatures and cardiovascular cause-specific mortality: results from 27 countries. Circulation 2023;147:35-46.
4. Hadley MB, Henderson SB, Brauer M, Vedanthan R. Protecting cardiovascular health from wildfire smoke. Circulation 2022;146:788-801.
5. Alexeeff SE, Deosaransingh K, Van Den Eeden S, Schwartz J, Liao NS, Sidney S. Association of long-term exposure to particulate air pollution with cardiovascular events in California. JAMA Netw Open 2023;6:e230561.
6. Desai Y, Khraishah H, Alahmad B. Heat and the heart. Yale J Biol Med 2023;96:197-203.
7. Peters A, Schneider A. Cardiovascular risks of climate change. Nat Rev Cardiol 2021;18:1-2.
8. Chen K, Dubrow R, Breitner S, et al. Triggering of myocardial infarction by heat exposure is modified by medication intake. Nat Cardiovasc Res 2022;1:727-31.
9. Cusick M, Rowland ST, DeFelice N. Impact of air pollution on running performance. Sci Rep 2023;13:1832.
10. Al-Kindi SG, Brook RD, Biswal S, Rajagopalan S. Environmental determinants of cardiovascular disease: lessons learned from air pollution. Nat Rev Cardiol 2020;17:656-72.