Air Pollution and Cardiovascular Health for Health Professionals - by Eugenia Miller, MD

Please find the short version of this article for non-professionals here.

Introduction

Many Americans are aware that air pollution is a problem for persons with underlying pulmonary (lung) disease and may be associated with cancer risk, yet few are aware of the negative impacts air pollution has on the cardiovascular health of the entire population.

When people are made aware of how they themselves are adversely affected by air pollution they may become more inspired to make changes in their personal and political behavior to benefit their own health that would also benefit air quality and the climate.

Sources of air pollution

Air pollution is a complex mixture that varies with location, time of day and weather. Its components include particulate matter (defined as coarse <10um, fine <2.5um and ultrafine <0.1um) and gases (carbon monoxide, sulfur dioxide, nitric oxides, and volatile and semi volatile organic compounds) released into the atmosphere and ozone formed in the atmosphere. (1) Ambient (outdoor) air pollution comes from natural and human sources. Natural sources include windblown dust and wildfires. Human sources include both stationary and mobile sources. Stationary human sources include coal fired power plants, industrial activity, agricultural dust, oil and gas wells and gas compressors. Mobile human sources include emissions from automobiles, trucks, ships, and airplanes. (6) Indoor air pollution sources include burning of wood, coal and natural gas, tobacco products, building materials and furnishings, aerosol sprays and volatile cleaning products. (1, 23)

Pollution is a risk factor for cardiovascular (CV) disease.

Cardiovascular disease remains the leading cause of death worldwide and has been the leading cause of death for the last century. Identification and treatment of standard risk factors for cardiovascular disease of hypertension, smoking, dyslipidemia, diabetes mellitus, inactivity and unhealthy diet have led to a 50% reduction in cardiovascular disease since 1950. (1) However, air pollution has been less well recognized as a risk factor despite its substantial contribution to the prevalence of cardiovascular disease.

The Global Burden of Disease Study estimates that air pollution accounts for 9 million deaths worldwide, with 61% related to cardiovascular disease including 31.7% secondary to coronary artery disease and 27.7% secondary to stroke. (1)

The Institute for Health Metrics Estimate found air pollution to be the fourth highest ranking risk factor for global mortality after hypertension, smoking and dietary risks. (5)

Particulate matter is the pollutant most implicated in adverse CV events

Particulate matter (PM) is the pollutant most implicated in cardiovascular disease morbidity and mortality. It has been shown to increase both acute and chronic cardiovascular morbidity (adverse health effects) and mortality. (4,6,)

The short term adverse effects of increases in particulate matter have been demonstrated by studies correlating hospital admission with levels of PM. Data from Chicago area hospitals from 1988-93 showed an increase in hospital admission for heart disease, COPD and pneumonia of 1.27%, 1.45% and 2.0% respectively for each increase particulate matter <10um (PM10) of 10ug/M3. (6)

Short term effects on mortality are evaluated in studies that associate levels of air pollutants over days to weeks prior to a death. A study in Coachella Valley California revealed that a 10ug/M3 increase in PM10 was associated with a 1% increase in total mortality. (6, 17)

Long term effects of elevated levels of pollutants have been evaluated in cohort studies spanning years. The Harvard Six Cities Study evaluated 14-to-16-year mortality in 8,111 adults in 6 US cities and demonstrated a 16% increase in mortality per 10ug/M3 in particulate matter <2.5 um (PM 2.5). (6) The American Cancer Society Study that linked mortality in 150 US cities with ambient air quality found a risk ratio of 1.17 for all causes of mortality associated with levels of PM 2.5. (6). A meta-analysis from the American Cancer Society study for 1979-2000 found increased mortality risk in categories of ischemic heart disease (risk ratio 1.18) and combined dysrhythmias, heart failure and cardiac arrest (risk ratio 1.13) for every 10ug/M3 increase in PM 2.5. (6)

Pollution worsens standard risk factors for cardiovascular disease.

Standard risk factors for cardiovascular disease are worsened by air pollution.  This is likely one of the mechanisms by which pollution increased cardiovascular morbidity and mortality. An increase in PM 2.5 of 10ug/M3 is consistently associated with a 1-3mm increase in systolic and diastolic blood pressure over the subsequent 2-3 days. Longer exposure to PM 2.5 is linked to chronic BP elevations. (3) The risk of diabetes mellitus has been documented to increase by 39% per 10ug/M3 of NO2. (3).

Subclinical atherosclerosis is associated with particulate matter pollution.

Carotid intima-medial thickness and coronary calcium scores are measures of subclinical cardiovascular disease. Increases in carotid intima-media thickness and coronary calcium scores have been associated with increases in PM 2.5 concentrations. (6)
 

Acute and chronic coronary atherosclerosis is associated with elevated PM.

Coronary plaque rupture is a common mechanism of acute coronary syndromes (ACS). A study in Rome of 126 patients presenting with ACS (ST elevation myocardial infarction (i.e. heart attack), non-ST elevation myocardial infarction and unstable angina) and studied with Ocular Coherence Tomography (OCT) showed 52.4% of patients with plaque rupture (plaque erosion and calcified plaque at the culprit site accounted for the other events). Two years of data relative to pollutants prior to the ACS events were correlated with the ACS events. PM 2.5 was significantly associated with plaque rupture and the precursors of plaque rupture: thin capped fibroadenoma and plaque macrophage infiltrates. (8) Levels of PM 10, PM 2.5 and CO correlated with increased levels of CRP in this study. (8)

73,426 US veterans undergoing elective percutaneous intervention (PCI) between 2005 and 2018 were followed for a median of 6.75 years. Each veteran was assigned a level of PM 2.5 exposure by ZIP code at the time of PCI and annually thereafter. For each 1 ug/M3 increase in PM 2.5 the incidence of subsequent major adverse cardiovascular events (MACE) increased by 8.7%, P<0.001. (9)

Compared to patients whose exposure was 5ug/M3, those whose exposure was 10ug/M3 lost 1.1, 3.8, and 7.6 months of life at 5, 10, and 15 years of follow up. (9)

Ventricular and atrial arrhythmias are associated with elevated PM.

Both atrial and ventricular arrhythmias have been associated with increases in PM 2.5. (3,6) Acute changes in heart rate and heart rate variability that may predispose to ventricular arrhythmias have been documented with increases in PM 10 and PM 2.5. (6,15)

211 patients with automatic implanted cardioverter defibrillators (AICDs) enrolled in a study in Sweden were evaluated relative to the correlation of PM 10 with symptomatic ventricular tachycardia (VT) or ventricular fibrillation (VF) that was treated with anti-tachycardia pacing (ATP) or shock or ATP followed by shock. The 2-hour moving average of PM 10 correlated with episodes of VT/VF with an odds ratio of 1.31, Confidence interval (1.00-1.72). (16)

Atrial fibrillation (AF) is the most common sustained arrhythmia in adults. It accounts for more days of hospitalization than any other arrhythmia. It may lead to stroke, heart attack, heart failure and death. A study of 176 patients with AICDs monitored for 90 days showed an increased incidence of AF occurring in association with an increase in the mean 2-hour moving average of PM 2.5 with a P value of 0.004. (4)

Biologic pathways linking air pollution to CV events

Air pollution is thought to exert its adverse CV effects through a variety of mechanisms. Particles deposited in the lungs increase oxidative stress and inflammation. (6,4) Ultrafine particles can directly enter the circulation at the alveolar capillary interface. Air pollution stimulates neural reflex arcs and autonomic imbalance. (5,3,6,4) These effects result in an increase in cardiovascular risk factors: hypertension, insulin resistance, dyslipidemia. They result in endothelial dysfunction, activation of the hypothalamic pituitary axis and pro-thrombosis. These factors then result in cardiovascular events. (3,5)

Figure 1. Biologic Pathways Linking Air Pollution with Cardiovascular Disease Mechanisms of cardiovascular disease attributable to air pollution exposure (adapted from Rajesh Vedanthan and Michael Hadley 2019)  

Figure reproduced from Brauer M, Casadei B, Harrington R, et al. Taking a Stand Against Air Pollution—The Impact on Cardiovascular Disease. J Am Coll Cardiol. 2021 Apr, 77 (13) 1684–1688. (5)

Government efforts to limit air pollution

Several severe urban pollution events clearly associated with major acute increases in hospitalization and death in the early twentieth century triggered public outrage and led to worldwide legislative activity and regulatory acts limiting the toxic and often deadly effects of air pollution. In the US this included the Clean Air Act of 1963 and the Air Quality Act of 1967. (6)

The Clean Air Act, last amended in 1990, requires the EPA to set National Ambient Air Quality Standards for 6 principal pollutants: C0, lead, N02, ozone, particle pollutants (PM2.5 and PM 10) and S02. The primary standard for public health protection set by the EPA for PM 2.5 is 12ug/M3 annual mean and 35 ug/M3 24 hour mean. (7) Between 1970 and 2018 there was a 74% reduction in aggregate emissions of the 6 common pollutants. (19)

Unfortunately for Colorado, the oil and gas industry obtained an exemption from the cumulative impacts provision of the Clean Air Act. Unlike other industries, such as automobile manufacture, aggregated point source pollution from multiple oil and gas production wells is exempt from air quality standards set forth in the act. (see p. 13 here). 17.6 million Americans live within a mile of an oil and gas well  (ref.)  

Currently in the US, the annual average population weighted PM 2.5 is approximately 10ug/M3. Similar improvement has not occurred in other countries particularly in southern and eastern Asia. The global annual average population weighted PM 2.5 is approximately 40ug/M3. In China it is approximately 50 ug/M3 and in India approximately 80ug/M3. (1) Despite these improvements in the US, in 2019 132 million people lived in US counties that were not in compliance with national air quality standards. (19) Extensive evidence demonstrates that there is no lower concentration threshold below which exposure can be considered safe. Studies from Europe and Canada show increased mortality associated with PM 2.5 at levels as low as 2 ug/M3. (3) Moreover, the concentration response curve is steeper at lower concentrations. This means that the risk of morbidity and mortality rise sharply at low concentrations and then somewhat level off at higher concentrations. (10)

Disparities in risk of adverse effects from air pollution

The adverse effects of ambient air pollution are greater among certain populations. These include those less than 5 years old, those over 60 years old and persons with established heart disease, hypertension, and diabetes. (3) A study of PM 2.5 exposure and mortality in the US Medicare population found higher mortality risks for men, blacks, and persons with Medicaid than the rest of the population. (13)

45 million people in the US live within 100 meters of a major roadway. Air pollutants from vehicles are in higher concentration near roadways. People who live near or spend significant time near roadways have a significant increase in health problems related to vehicle pollution including cardiovascular disease.  (19)

Schools serving black students are 18% more likely to be located within 250 meters of a major roadway. Hispanic children are 1.5 times more likely to live near a major roadway than white children. (19)

Because of racial discrimination in housing and lending (such as redlining), people of color are more likely to reside in areas of higher risk for increased levels of pollution. (12)  Black and low-income people have higher exposure to fossil fuel power plants. These plants were built in more densely populated areas with greater proximity to minority populations. A study correlating PM 2.5 emissions in the 2011 National Emissions Inventory with nearby block groups across the 2001-2013 American Community Survey population found that exposure to PM 2.5 was higher than that of the overall population by a factor of 1.25 for nonwhites and by a factor of 1.54 for blacks. These disparities held nationally and within most states and counties. (14)

Gas production especially at well sites that use fracking produce potent carcinogens, diesel exhaust, fine particulates, and nitrogen oxides. (20) Drilling and operating gas and oil and gas wells are disproportionately located near communities of color and indigenous communities. (11)

Communities of color, indigenous communities and minority ethnic groups are disproportionately affected by wildfires. These groups have higher rates of outdoor work. They have poorer quality housing where outdoor air pollutants are more likely to penetrate indoors. (11)

Communities of color, indigenous communities and minority ethnic groups have a higher prevalence of existing respiratory and cardiovascular conditions making them more vulnerable to adverse effects of air pollution. They also experience significant barriers to health care. (11)

Indoor air pollution

Indoor air pollution has not received the attention that outdoor (ambient) air pollution has. Indoor air pollution is not regulated by the EPA. However, since most US adults, particularly urban residents typically spend 90% of their time indoors, indoor air pollution is an important concern. (20,23) Indoor air pollution sources include burning of wood, coal and natural gas, tobacco products, building materials and furnishings, aerosol sprays and volatile cleaning products. Outdoor air pollution can also penetrate indoors to cause indoor air pollution. (1, 23)

A review of research on indoor air pollution found that the major indoor sources of PM 2.5 in the US and the UK were cooking and smoking. There was wide variation in mean concentrations of PM 2.5. Reported levels varied from 1.7 ug/M3 in Quebec City, Canada to 428.6 ug/M3 in Dubai in homes with hookah (water pipe). (20)

Harmful effects of indoor air pollution are demonstrated by research showing the benefit of use of air filters to reduce exposure to indoor pollution.

In a randomized blinded crossover study of 35 healthy college students in Shanghai, China where outdoor air pollution was the major source of indoor air pollution the average outdoor PM 2.5 was 103 ug/M3, unfiltered indoor PM 2.5 was 96.2 ug/M3 and filtered indoor PM 2.5 was 41.3 ug/M3, a 57% reduction. Measures of inflammatory biomarkers and both systolic and diastolic blood pressure were significantly reduced with the air filtration. (18)  In a study in Sweden of the effect of indoor air particles on vascular function 21 couples age 60 to 75 were exposed in a crossover manner to particle filtered and nonfiltered indoor air. Noninvasively assessed microvascular function was improved by 8.1% (CI 0.4-16.3) with filtration of air for 48 hours. (22)

Strategies to mitigate air pollution and its adverse effects

Personal strategies

Personal strategies to reduce or eliminate exposure to pollutants are particularly applicable to individuals living in or traveling to certain Asian nations such as China and India where ambient pollutants are routinely at very high levels. Personal strategies are particularly applicable to persons at high risk for adverse effects of pollutants such as those with preexisting cardiac and pulmonary disease. Such strategies are particularly important for persons who are exposed to microenvironments with higher levels of pollutants such as urban environments, persons living within 100 meters of a major roadway and persons exposed to wildfires and dust storms. (24)

Several scientific societies have made recommendations based on the best current evidence. (21, 24)

Limit exposure. The EPA’s Air Quality Index (AQI) converts concentrations of 5 regulated pollutants (CO, NO2, ozone, PM, and SO2) into levels of increasing health risk both for healthy and persons at increased health risk. Recommendations regarding activity are available for each level for healthy persons and persons at increased health risk. Although only a minority of the population follows these recommendations, those who do can reduce their individual exposure. (24)  Metropolitan areas with populations above 350,000 are required to report the AQI to the public daily. Many smaller municipalities report the AQI as well. The EPA’s web site, airnow.gov, can be used to determine the AQI updated hourly by zip code and a AQI forecast if available.

N95 masks. N95 masks filter 95% of particles > 0.3 um. (2) Use of the N95 mask may be a wise choice in situations of high pollutant exposure such as with wildfires, dust storms or severe urban pollution events.

Portable Air Cleaners (PACs). PACs are small units designed for cleaning small areas such as a single room. They are mechanical air filters that capture particles on filter material. Use of PACs has been shown to reduce PM 2.5 by as much as 50 to 60%. PACs were used in the air filter studies cited above in China and Sweden.

HVAC units with HEPA filters. Central heating, ventilation, and air conditioning units (HVAC) equipped with high efficiency particulate arrestance filters (HEPA) can be an effective means for uniform reductions in particles. However, there are currently no clear studies showing health benefits of filters in forced air systems. (24)

Antioxidant supplementation. Because adverse effects of air pollution are thought to be mediated in part by oxidative stress several studies have looked at possible benefit from supplementation with antioxidant medication such as vitamin C, vitamin E and fish oil. There is no clear evidence that antioxidant over the counter medication or commonly used prescription medicines for primary and secondary prevention of cardiovascular disease have a role to decrease pollution induced cardiovascular risk. However, use of medicines for primary and secondary prevention of cardiovascular disease are encouraged when prescribed for other reasons. (24)

Personal strategies related to indoor air pollution

Avoiding tobacco products is recommended based on tobacco’s causative role in a myriad of health problems but also because of its role in increasing indoor air pollution.

Cooking and heating with fossil fuels is a major source of indoor air pollution. Transitioning from cooking and heating with natural gas or wood pellets to electric induction cook tops/ranges and heat pumps has the potential to significantly decrease indoor air pollution.

Opportunity for global impact on air pollution

Although actions at the individual and personal level to mitigate adverse effects of air pollution are important, action on the community, state, regional, national, and global level is needed to achieve major reductions in air pollution attributable morbidity and mortality. The American Heart Association (AHA) in a statement issued in 2020 (19) and the AHA along with the World Heart Federation, American College of Cardiology and the European Society of Cardiology in a statement in 2021 (5) acknowledged the need for further research regarding air pollution’s effects on cardiovascular health and dissemination of that research, advocacy of policy solutions to reduce pollution and education of physicians and patients regarding the cardiovascular effects of air pollution. (19,5)

Policy advocacy should address reduction in emissions through action on air quality, action on vehicle emissions and promotion of renewable energy generation.  Policy interventions should align with policies that benefit community, address health disparities, promote healthy transportation infrastructure, support sustainable food systems, produce reductions in climate forcing agents and reduce frequency and intensity of wildfires. Such policies are intimately interrelated with improvements in each ultimately capable of reducing air pollution’s morbidity and mortality. Advocacy should address not just government policy but private sector action and public private partnerships. (19)

Air quality benefits work on shorter time frames, provide large decreases in cardiovascular morbidity and mortality, work more locally and are likely to be more readily accepted by those concerned with the cost of broader long term climate policies. (19)

The cardiovascular community and the larger health care community need to make policy changes as well. The health care sector is responsible for a significant amount of total US air pollution. The largest amount comes from energy generation. From 2003 to 2013 there was a 28% increase in greenhouse gas emissions from health care facilities. (19) The health care sector needs to set an example by reducing its emissions.

Figure 2. Impact of air pollutant drivers and mitigators on human health. This figure demonstrates the interplay between predictors of air quality and the predictors of climate change. There is substantial overlap between the drivers of poor air quality and increased greenhouse gases. Policies to reduce concentrations of ambient air pollutants will have other environmental benefits. Similarly, policies to reduce greenhouse gases and slow climate change will have health cobenefits through reduction in ambient air pollutant concentrations.

Figure reproduced from Kaufman, J, Elkind, M et al. Guidance to Reduce the Cardiovascular Burden of Ambient Air Pollutants: A Policy Statement from the American Heart Association. Circ 2020 Dec, 142 (23) e432-e447 (19)

Summary and conclusions

Air pollution especially pollution related to fine particles (PM2.5 and PM 10) has significant adverse effects on cardiovascular health. These adverse effects occur even at the usual relatively low levels of particulates normally present in most US communities.

Because of disparities related to race and ethnicity many persons and communities are exposed to higher levels of pollutants and experience worse health outcomes.

Indoor air pollution, primarily related to burning of fossil fuels for heating and cooking as well as tobacco smoke, has significant adverse health effects particularly since most US citizens spend 90% of their time indoors.

Actions at the personal level to mitigate air pollutions effects include adjusting activity based on the daily AQI, using portable air cleaners and in highly polluted circumstances using N95 masks.

Additional research and dissemination of that research, policy advocacy at the government and private sector level and education of physicians and patients may improve air pollution by better addressing its sources.

Causes and solutions for air pollution overlap significant with causes and solutions for climate change. To achieve success, we need to address both.

References

1.   Sanjay Rajagopalan and Philip Landrigan Pollution and the Heart, N Eng J Med 2021: 385:1881-92

2.   Newman J, Bhatt D, Rajagopalan S, et al. Cardiopulmonary Impact of Particulate Air Pollution in High-Risk Populations. J Am Coll Cardiol. 2020 Dec, 76 (24) 2878–2894.

3.   Rajagopalan S, Al-Kindi S, Brook R, et al. Air Pollution and Cardiovascular Disease. J Am Coll Cardiol. 2018 Oct, 72 (17) 2054–2070.

4.   Link M, Luttmann-Gibson H, Schwartz J, et al. Acute Exposure to Air Pollution Triggers Atrial Fibrillation. J Am Coll Cardiol. 2013 Aug, 62 (9) 816–825.

5.   Brauer M, Casadei B, Harrington R, et al. Taking a Stand Against Air Pollution—The Impact on Cardiovascular Disease. J Am Coll Cardiol. 2021 Apr, 77 (13) 1684–1688.

6.   Simkhovich B, Kleinman M, Kloner R, et al. Air Pollution and Cardiovascular Injury. J Am Coll Cardiol. 2008 Aug, 52 (9) 719–726.

7.  Reviewing National Ambient Air Quality Standards: Scientific and Technical Information, https://www.epa.gov/naaqs

8.  Montone R, Camilli M, Russo M, et al. Air Pollution and Coronary Plaque Vulnerability and Instability. J Am Coll Cardiol Img. 2022 Feb, 15 (2) 325–342.

9.  Motairek I, Deo S, Elgudin Y, et al. Particulate Matter Air Pollution and Long-Term Outcomes in Patients Undergoing Percutaneous Coronary Intervention. JACC Adv. 2023 May, 2 (3) .

10. Liu, C, Chen R., et al. Ambient Particulate Air Pollution and Daily Mortality in 652 Cities. N Engl J Med 2019; 381:705-715

11. Morello-Frosch, R and Obasogie, O. The Climate Gap and the Color Line—Racial Health Inequalities and Climate Change. N Engl J Med 2023; 388:943-949

12. "Communities, Climate Change, and Health Equity: Proceedings of a Workshop - in Brief." National Academies of Sciences, Engineering, and Medicine. 2022. Communities, Climate Change, and Health Equity: Proceedings of a Workshop–in Brief. Washington, DC: The National Academies Press. doi: 10.17226/26435.

13. Di, Q, Wang, Y, et al. Air Pollution and Mortality in the Medicare Population. N Engl J Med 2017; 376:2513-2522
DOI: 10.1056/NEJMoa1702747

14. Ihab Mikati, Adam F. Benson, Thomas J. Luben, Jason D. Sacks, Jennifer Richmond-Bryant, “Disparities in Distribution of  Particulate Matter Emission Sources by Race and Poverty Status”, American Journal of Public Health 108, no. 4 (April 1, 2018): pp. 480-485.

15. Sivagangabalan G, Spears D, Masse S, et al. The Effect of Air Pollution on Spatial Dispersion of Myocardial Repolarization in Healthy Human Volunteers. J Am Coll Cardiol. 2011 Jan, 57 (2) 198–206.

16. Petter L.S. Ljungman and others, Rapid effects of air pollution on ventricular arrhythmias, European Heart Journal, Volume 29, Issue 23, December 2008, Pages 2894–2901,

17. Ostro, B., Hurley, S, and Lipsett, M. Air Pollution and Daily Mortality in the Coachella Valley California: A Study of PM10 Dominated by Coarse Particles. Environ Res 1999, 81 (3): 231-238.

18. Chen R, Zhao A, Chen H, et al. Cardiopulmonary Benefits of Reducing Indoor Particles of Outdoor Origin. J Am Coll Cardiol. 2015 Jun, 65 (21) 2279–2287.

19. Kaufman, J, Elkind, M et al. Guidance to Reduce the Cardiovascular Burden of Ambient Air Pollutants: A Policy Statement from the American Heart Association. Circ 2020 Dec, 142 (23) e432-e447

20. Vardoulakis, S, Giagloglou, E, et al. Indoor Exposure to Selected Air Pollutants in the Home Environment: A Systematic Review. Int. J. Environ. Res. Public Health 2020, 17(23), 8972

21. Hung A, Koch S, Bougault V, et al. Personal strategies to mitigate the effects of air pollution exposure during sport and exercise: a narrative review and position statement by the Canadian Academy of Sport and Exercise Medicine and the Canadian Society for Exercise Physiology. British Journal of Sports Medicine 2023; 57:193-202.

22. Brauner, E, Forchhammer, L et al. Indoor Particles Affect Vascular Function in the Aged. Am J Respir Crit Care Med 2008, 177: 419-25.

23. Indoor Air Quality. Air Cleaners and Air Filters in the Home. https://www.epa.gov

24. Rajagopalan, S., Brauer, M et al. Personal-level Protective Actions Against Particulate Matter Air Pollution Exposure: A Scientific Statement from the American Heart Association. Circ 142 (23) Dec 2020, e411-431.