The Importance of Identifying At-Risk Populations to Air Pollution Exposures and Quantifying Risks in Populations with Multiple Risk Factors

FOR RELATED ARTICLE, SEE PAGE 825The causal relationship between short-term and long-term exposure to fine particulate matter (PM2.5) and cardiovascular disease and death are well-established.1US Environmental Protection AgencyIntegrated Science Assessment (ISA) for Particulate Matter (Final Report, Dec 2019). US Environmental Protection Agency, Washington, DC2019Google Scholar,2US Environmental Protection AgencySupplement to the 2019 Integrated Science Assessment for Particulate Matter (Final Report, 2022). US Environmental Protection Agency, Washington, DC2022Google Scholar The US Environmental Protection Agency's National Ambient Air Quality Standards are intended to protect public health with an adequate margin of safety, which includes protection for groups potentially at increased risk for health effects from exposure to criteria air pollutants like PM2.5. Although it is generally accepted that health effects from PM2.5 exposure may be modified as a result of intrinsic factors (eg, preexisting disease, genetics, epigenetics) or extrinsic factors (eg, social determinants of health or behavioral patterns), relatively few epidemiologic studies quantify the potential effect of the measure modification by these factors, and the groups that are most at risk to the effects of air pollution are still uncertain. In this issue of CHEST, Aron et al3Aron J. Baldomero A.K. Rau A. Fiecas M.B. Wendt C.H. Berman J.D. Individual risk factors of PM2.5 associated with wintertime mortality in urban patients with COPD.Chest. 2024; 165: 825-835Google Scholar estimate the association between short-term PM2.5 exposure and all-cause death among veterans with preexisting COPD using a case-crossover design. In addition, they evaluate the potential for modification of the association by other preexisting diseases (coronary artery disease [CAD], diabetes mellitus, obesity) and sociodemographic factors (race, area deprivation index). Aron et al3Aron J. Baldomero A.K. Rau A. Fiecas M.B. Wendt C.H. Berman J.D. Individual risk factors of PM2.5 associated with wintertime mortality in urban patients with COPD.Chest. 2024; 165: 825-835Google Scholar report higher ORs for an increase in PM2.5 exposure and all-cause death among veterans with preexisting COPD when the same individuals also have CAD, diabetes mellitus, and/or obesity. We commend these authors for diligent evaluation of each of these factors. Their results provide valuable insights to inform regulatory actions, health protective individual behaviors, and clinical interventions. FOR RELATED ARTICLE, SEE PAGE 825 In particular, Aron et al3Aron J. Baldomero A.K. Rau A. Fiecas M.B. Wendt C.H. Berman J.D. Individual risk factors of PM2.5 associated with wintertime mortality in urban patients with COPD.Chest. 2024; 165: 825-835Google Scholar investigate a very specific, relatively large, and well-characterized population, veterans with COPD, during the winter months when exposure most likely will exacerbate a health response. The case-crossover approach controls for time-stable confounding factors, which is of importance in a veteran population in which individuals may have experienced a wide variety of detrimental exposures over their lives and service. However, the case-crossover design does not allow for direct comparison of subpopulations. To investigate potential effect modification, the authors used stratification and estimate ORs for each subpopulation independently and then compared the ORs for the subpopulation to the OR for the overall population. This method allows for identification of potentially at-risk populations while benefiting from the strengths of the case-crossover design, but full assessment of interaction is not possible. In the 2019 Particulate Matter Integrated Science Assessment,1US Environmental Protection AgencyIntegrated Science Assessment (ISA) for Particulate Matter (Final Report, Dec 2019). US Environmental Protection Agency, Washington, DC2019Google Scholar,2US Environmental Protection AgencySupplement to the 2019 Integrated Science Assessment for Particulate Matter (Final Report, 2022). US Environmental Protection Agency, Washington, DC2022Google Scholar there was "suggestive evidence" that populations with preexisting cardiovascular or respiratory disease, those who are overweight or obese, and those with low socioeconomic status were at increased risk for PM2.5-related health effects. The results reported by Aron et al3Aron J. Baldomero A.K. Rau A. Fiecas M.B. Wendt C.H. Berman J.D. Individual risk factors of PM2.5 associated with wintertime mortality in urban patients with COPD.Chest. 2024; 165: 825-835Google Scholar will contribute to the overall body of evidence that supports this conclusion and may aid in the reduction of uncertainties that are associated with the existing evidence. One uncertainty Aron et al3Aron J. Baldomero A.K. Rau A. Fiecas M.B. Wendt C.H. Berman J.D. Individual risk factors of PM2.5 associated with wintertime mortality in urban patients with COPD.Chest. 2024; 165: 825-835Google Scholar do not address is what effect (if any) that preexisting COPD has on the association between short-term PM2.5 exposure and all-cause death. If the relationship between PM2.5 and all-cause death was evaluated previously in the veterans cohort, those results could provide context and aid in interpreting the results in a COPD population. For example, it is unclear whether the modification of the effect by CAD (in addition to COPD) would be different among individuals with CAD (or diabetes mellitus or obesity) but without COPD. In the report by Aron et al3Aron J. Baldomero A.K. Rau A. Fiecas M.B. Wendt C.H. Berman J.D. Individual risk factors of PM2.5 associated with wintertime mortality in urban patients with COPD.Chest. 2024; 165: 825-835Google Scholar there is always one (potential) modifier–COPD–and then more are added. Although pairing other potential modifiers with COPD provides important information, it does not help reduce uncertainties related with COPD alone. Still, this study provides important evidence to further highlight populations at increased risk from air pollution exposures, and we hope that it will influence others to conduct similar analyses. Evidence from such studies is vital to examine interactions, effect measure modification, and joint effects that are associated with preexisting disease, social determinants of health, and air pollution exposure as we work to increase awareness to and demonstrate the feasibility of conducting cumulative impact studies. In addition, the evaluation of effect measure modification by preexisting disease or sociodemographic characteristics provides important information to clinicians as they counsel their patients and discuss the health implications that are associated with exposure to air pollution. The evidence provided in studies like the one by Aron et al3Aron J. Baldomero A.K. Rau A. Fiecas M.B. Wendt C.H. Berman J.D. Individual risk factors of PM2.5 associated with wintertime mortality in urban patients with COPD.Chest. 2024; 165: 825-835Google Scholar helps to improve clinical awareness of environmental risk factors for cardiovascular disease, respiratory disease, and death. By providing health care professionals with information about the detrimental health effects of air pollution and the disparities in these effects by underlying health status or demographic characteristics, clinicians can make informed decisions about recommended changes to personal behavior or potential interventions or treatments for individuals most at risk. This allows individuals to optimize healthy behaviors and clinical management of health conditions for those most at risk of the effects of air pollution. For example, individuals may choose to reduce air pollutant exposures by adjusting the type of outdoor activities or the time spent outdoors, using in-home HEPA filtration, or wearing a high-efficiency respirators (eg, N95 masks) outdoors when air pollution concentrations are high.4Rajagopalan S. Brauer M. Bhatnagar A. et al.Personal-level protective actions against particulate matter air pollution exposure: a scientific statement from the American Heart Association.Circulation. 2020; 142: e411-e431Crossref PubMed Scopus (108) Google Scholar Recent studies have demonstrated the utility of in-home air cleaners for PM2.5 reduction from wildfires5Belz D.C. Myers L.C. Hansel N.N. Cardiopulmonary health burden of wildfire particulate exposure urges us to consider interventions.Am J Respir Crit Care Med. 2023; 207: 807-809Crossref Scopus (0) Google Scholar and for improved respiratory symptoms for patients with COPD as a direct result of ambient PM2.5 reduction.6Woo H. Koehler K. Putcha N. et al.Principal stratification analysis to determine health benefit of indoor air pollution reduction in a randomized environmental intervention in COPD: results from the CLEAN AIR study.Sci Total Environ. 2023; 868161573Crossref Scopus (1) Google Scholar Potential benefits from antiinflammatory treatments and nutritional supplements that could reduce the impacts of air pollutant exposures7Sherratt S.C. Libby P. Dawoud H. Bhatt D.L. Malinski T. Mason R.P. Eicosapentaenoic acid (EPA) reduces pulmonary endothelial dysfunction and inflammation due to changes in protein expression during exposure to particulate matter air pollution.Biomed Pharmacother. 2023; 162114629Crossref Scopus (3) Google Scholar, 8Tong H. Rappold A.G. Diaz-Sanchez D. et al.Omega-3 fatty acid supplementation appears to attenuate particulate air pollution-induced cardiac effects and lipid changes in healthy middle-aged adults.Environ Health Perspect. 2012; 120: 952-957Crossref Scopus (83) Google Scholar, 9Tong H. Zhang S. Shen W. et al.Lung function and short-term ambient air pollution exposure: differential impacts of omega-3 and omega-6 fatty acids.Ann Am Thorac Soc. 2022; 19: 583-593Crossref PubMed Scopus (13) Google Scholar are being explored, though general evidence for dietary changes and pharmacotherapy is mixed.4Rajagopalan S. Brauer M. Bhatnagar A. et al.Personal-level protective actions against particulate matter air pollution exposure: a scientific statement from the American Heart Association.Circulation. 2020; 142: e411-e431Crossref PubMed Scopus (108) Google Scholar Overall, the analyses by Aron et al3Aron J. Baldomero A.K. Rau A. Fiecas M.B. Wendt C.H. Berman J.D. Individual risk factors of PM2.5 associated with wintertime mortality in urban patients with COPD.Chest. 2024; 165: 825-835Google Scholar in this issue of CHEST will aid in the identification of potential intervention points at the individual (eg, clinical and behavioral) and policy (eg, government actions, regulations) levels. We encourage others in the scientific community to consider the feasibility and appropriateness of including these types of analyses in future air pollution and health research. Results from such studies will be useful in the characterization of the role of air pollution as part of the greater cumulative impact of ubiquitous environmental and social stressors. None declared. Disclaimer: The views expressed in this article are those of the author(s) and do not necessarily represent the views or policies of the US Environmental Protection Agency. Individual Risk Factors of PM2.5 Associated With Wintertime Mortality in Urban Patients With COPDCHESTVol. 165Issue 4PreviewWintertime PM2.5 exposure was associated with elevated mortality risk in people with COPD, but individuals with multiple comorbidities, notably obesity, had high vulnerability. Our study suggests that obesity, CAD, and diabetes are understudied modifiers of air pollution-related risks for people with existing COPD. Full-Text PDF