Environmental Health Perspectives • volume 117 | number 9 | September 2009 

### 1351 

# Review

There is growing interest within environ

mental health in disentangling effects of clus

tered social and environmental exposures and exploring potential synergies among these
exposures (Gee and Payne-Sturges 2004; Morello-Frosch and Shenassa 2006; O’Neill

et al. 2003, 2007 a, 2007b ; Weiss and Bellinger 2006). This interest stems from the observation that social stressors (i.e., violence, poverty) and environmental exposures (i.e., traffic-related and industrial air pollution) are often spatially correlated and may cluster in lower-income communities, often in locations with lower property values along highways and industrialcorridors (Bullard 1990; Graves 1988). Trafficrelated air pollution is a complex chemical mix (Schauer et al. 2006), often spatially associ

ated with noise, poverty, and other stressors (Wheeler and Ben-Shlomo 2005). Social stres

sors may lead to poor health outcomes directly or may increase susceptibility to physical expo

sures, such as air pollution, through alterations in immune function and biological systems (McEwen and Seeman 1999). Thus, the most pollution-exposed communities may also be more susceptible because of higher prevalence of social stressors (Lipfert 2004). This poten

tial for spatial confounding and effect modifi

cation by social stressors presents a challenge to air pollution epidemiology. Disentangling social and physical environmental risks (U.S. Environmental Protection Agency 2008), understanding synergies among these expo
sures , and identifying modifiable exposures are particularly important for understanding how best to protect susceptible populations and improve overall population health.There is significant evidence linking trafficrelated pollution exposure to respiratory ill

ness. Chronic exposure to traffic-related and particulate air pollution among adults has been linked to upper respiratory tract inflammation (Hiltermann et al. 1997), chronic obstructive pulmonary disease (COPD) (Schikowski et al. 2005), lung cancer (Vineis et al. 2007), and premature mortality (Dockery 1993; Pope et al. 1995). In children, traffic-related pollution exposures, often indicated by residential prox

imity to major roads, has been associated with airway hyperresponsiveness (Jang et al. 2003), wheeze (Ryan et al. 2007), asthma (McConnell

et al. 2006), reduced lung function (Pekkanen

et al. 1997), and asthma-related hospitalizations (Lin et al. 2002; Moore et al. 2008). There is now increased interest in understanding car

diovascular effects (Peters 2005; Rückerl et al. 2006), identifying causal constituents (Lanki

et al. 2006), and characterizing susceptible sub

populations (O’Neill et al. 2007b). Psychological stress results when exter

nal demands exceed an individual’s perceived abilities and resources to meet those demands (Cohen et al. 1995) and has been linked to respiratory disease and other illness. L imited but growing epidemiologic evidence indi

cates that psychological stress may also alter susceptibility to physical exposures, such as air pollution

. This work examined social– environmental interactions in respiratory and cardiovascular disease, such as stress-related modification of traffic-related air pollution effects on asthma etiology (Clougherty et al. 2007) or exacerbation (Chen et al. 2008). There is also evidence of stress-related modi

fication in the relationship between bone lead level and hypertension among older men (Peters et al. 2007)

. In the same data set, we recently identified modification by stress in the relation between bone lead and heart rate variability (Clougherty JE, Peters JL, Schwartz J, Kubzansky L, unpublished data). One possible pathway for these differential susceptibilities is allostatic load (McEwen and Seeman 1999). Allostasis (literally, “achiev

ing stability through change”) refers to the body’s ability to adapt to transient stressors and exposures. Over time, chronic psycho

logical stress and maladaptive behaviors (e.g., poor diet, sleep deprivation) (McEwen 2006) may impair the body’s ability to maintain allostasis, producing wear and tear on bodily systems, compromised immune function, and enhanced general susceptibility (McEwen 2006; McEwen and Seeman 1999), and enhancing responsivity to environmental toxi

cants including air pollution. For example, some toxicologic evidence suggests perma

nent alteration in hypothalamic–pituitary– adrenal ( HPA ) function associated with chronic stress and lead exposures (Virgolini

et al. 2005, 2006). However, some biological systems involved in maintaining allostasis may also be worn down by repeated exposure to physical toxicants, as particle exposures may influence HPA function (Sirivelu et al. 2006). Finally, some air pollutants and psycho

social stress may independently affect com

mon physiologic processes such as oxidative

Address correspondence to J.E. Clougherty, Harvard School of Public Health, Landmark Building, 4th Floor West, Boston, MA 02215 USA. Telephone: (617) 816-7717. Fax: (617) 384-8859. E-mail: jcloughe@hsph.harvard.edu

We are very grateful to B. McEwen for his helpful suggestions on this manuscript.

The authors declare they have no competing financial interests.

Received 23 January 2009; accepted 12 May 2009. 

## A Framework for Examining Social Stress and Susceptibility to Air Pollution in Respiratory Health
Jane E. Clougherty 1 and Laura D. Kubzansky 2

1 Department of Environmental Health, and 2 Department of Society, Human Development, and Health, Harvard School of Public Health, Boston, Massachusetts, USA

O bjective : There is growing interest in disentangling the health effects of spatially clustered social and physical environmental exposures and in exploring potential synergies among them , with particular attention directed to the combined effects of psychosocial stress and air pollution. Both exposures may be elevated in lower-income urban communities, and it has been hypothesized that stress, which can influence immune function and susceptibility, may potentiate the effects of air pol

lution in respiratory disease onset and exacerbation. In this paper, we attempt to synthesize the rele

vant research from social and environmental epidemiology, toxicology, immunology, and exposure assessment to provide a useful framework for environmental health researchers aiming to investigate the health effects of environmental pollution in combination with social or psychological factors.
D ata synthesis : We review the existing epidemiologic and toxicologic evidence on synergistic effects of stress and pollution, and then describe the physiologic effects of stress and key issues related to measuring and evaluating stress as it relates to physical environmental exposures and sus

ceptibility. Finally, we identify some of the major methodologic challenges ahead as we work toward disentangling the health effects of clustered social and physical exposures and accurately describing the interplay among these exposures

. C o nclusi o ns : There is still tremendous work to be done toward understanding the combined and potentially synergistic health effects of stress and pollution. As this research proceeds, we

recom mend careful attention to the relative temporalities of stress and pollution exposures, to non

linearities in their independent and combined effects, to physiologic pathways not elucidated by epidemiologic methods, and to the relative spatial distributions of social and physical exposures at multiple geographic scales.
K

ey w o r

d s : air pollution, social stress, spatial analysis, synergistic effects, urban community health. Environ Health Perspect 117:1351–1358 (2009). doi:10.1289/ehp.0900612 available via http:// dx.doi.org/ [Online 12 May 2009]Clougherty and Kubzansky



### 1352 volume 117 | number 9 | September 2009 • Environmental Health Perspectives stress (Fugisawa 2005) or inflammatory cell [immunoglobulin E (IgE) ] production (DiazSanchez et al. 2000; Nel 2001). More studies have explored air pollution effect modification by socioeconomic status ( SES ) than by stress. Given other evidence of greater stress-related illness and susceptibility among persons with lower SES (Kubzansky

et al. 2000; Miller and Chen 2007; Seeman

et al. 2004), heightened air pollution responses with lower SES may be mediated through stress-related pathways. The American Cancer Society (ACS) studies reported stronger effects of air pollution on respiratory, cardiovascu

lar, and all-cause mortality among lower-SES persons (Krewski et al. 2000), supported by other studies reporting stronger air pollution– health associations among less-educated adults (Finkelstein et al. 2003; Hoek et al. 2002; Pope 2002). Time-series studies have indi

cated that lower-SES persons display stronger associations between short-term air pollution exposures and health (Jerrett et al. 2004; Lin

et al. 2004; Martins et al. 2004), although not consistently (Zanobetti 2000). These stud

ies, however, have not explored specific com

ponents of SES that may be responsible for susceptibility effects, al though stress has been proposed as a key component. Several theoretical perspectives suggest that social, economic, and psychological dis

advantage may cluster (Adler and Matthews 1994; Evans and English 2002; Link and Phelan 2000; Shonkoff and Phillips 2000)

. Fundamental causes theory , for example, describes social conditions (e.g., socioeconomic position) as determinants of resource access and psychological and behavioral experience, shaping disease risk (Link and Phelan 1995). Although applicable to combined social and physical exposures, these theories have not addressed methodologic issues (e.g., spatial cor

relation, confounding, measurement bias) or interpretation challenges arising in combining theory, methods, and data across disciplines. Like air pollution, low SES and stressors (e.g., noise) may be elevated in urban settings along highways and industrial areas, and methods are needed to disentangle effects of clustered social and physical stressors and to investigate poten

tial synergies. One model (Morello-Frosch and Shenassa 2006) captures our key constructs of interest: a ) varied stressors at the individual and community level contribute to individual chronic stress; b ) chronic individual stress is embodied as allostatic load, or physiologic wear and tear, influencing individual susceptibility; and c ) stress-borne physiologic susceptibility may shape response to environmental expo

sures, including internal dose, resiliency, likeli

hood of developing a given illness, and ability to recover from it. Like other models combining social and physical exposures (deFur et al. 2007; Gee and Payne-Sturges 2004; O’Neill et al. 2003), the Morello-Frosch model acknowledges that some community-level stressors are also physical hazards (e.g., poor housing quality), complicating distinctions between effects of psychosocial and physical factors. This model frames our discussion, al though it is outside the scope of our review to describe the myriad possible social, political, and economic forces that contribute to individual stress

. Instead

, we focus our attention on individual-level stress and pollution susceptibility, given that higher-level stressors need be individually embodied to modify pollution effects through stress-specific pathways. We build on conceptual models of social– environmental interaction by describing key methodologic and conceptual issues that arise when merging data and methods from across environmental and social science tra

ditions. We hope to foster more integrative approaches toward understanding combined health effects of social and physical environ

mental exposures. We attempt to synthesize the literature to date on the following: •	Effects of stress on respiratory health and

susceptibility •	Epidemiologic and toxicologic evidence of

synergistic effects of stress and pollution •	Pathways through which stress may influ

ence pollution susceptibility •	Methodologic challenges in merging data

and methods from environmental and social sciences.

We aim to provide a template for research

ers aiming to rigorously consider combined effects on health across disciplines. We hope to support the growing literature targeted at dis

entangling effects of spatially clustered social and environmental exposures and exploring potential synergies among these exposures. 

### Physiologic Effects of Psychological Stress on Respiratory Health and Susceptibility A long history of research links psychological stress and respiratory health. In Treatise on Asthma

, Maimonides (1135–1204) described the illness

— “ Whereas treatment of asthma is important, treatment of a patient as a whole is more important. For asthma the physi

cian must be a doctor in every sense”—and described the importance of clean air and its interplay with emotions and hormones (Muntner 1963). In the 1930s, Hans Selye recognized links between chronic stress in laboratory rats and nonspecific susceptibility to respiratory distress and death (Selye 1936). More recently, chronic stress has been linked to asthma symptoms in cross-sectional studies (Oh et al. 2004), and prospective studies link caregiver stress to infant wheeze (Wright et al. 2002). Among asthmatic adolescents, SES has been associated with stress-linked immune mediators [interleukin (IL ) -5, interferon

- γ ], an association mediated by stress and con

trol beliefs (Chen et al. 2003). Acute stressors (e.g., violent events) may trigger asthma epi

sodes (Sandberg et al. 2000, 2004), and older individuals with greater psychological distress and anger display faster lung function decline over time (Kubzansky et al. 2002). Distinctions between acute (short-term, generally lasting days to weeks) and chronic (longer-term, lasting weeks to years) stress is not always clear

. Some severe acute stressors (e.g., sexual violence, or combat) can pro

duce chronic stress effects (i.e., post-traumatic stress disorder). Assessing stress chronicity is important, however, as acute and chronic stress can produce substantively different physiologic sequelae, and the predominance of acute versus chronic stress experience in a given period may shape observed relationships between stress and susceptibility. Acute stress is linked to sympathetic innervation, includ

ing increased ventilation and bronchodilation, plausibly masking some short-term effects air pollution effects (e.g., acute irritation, broncho constriction). Conversely, chronic stress can produce wear and tear on bodily sys

tems, weaken immune function, and increase pollution susceptibility. Because of these very different physiologic sequelae, careful consid

eration of stress chronicity and of the relative chronicities of stress and pollution exposures is critical in accurately characterizing their inter

play and in interpreting interactions. Acute stress, sympathetic regulation, and the fight-or-flight response. Sympathetic ner

vous system activation under acute stressproduces the immediate, short-term fightor-flight response. Neural synapses produce catecholamines (e.g., epinephrine and nor

epinephrine or adrenaline and nor adrenaline), and catabolic functioning breaks down metabo lites for physical activity and energy expenditure. Glucocorticoids are produced, including cortisol, increasing heart rate, ventilation, myocardial contraction force, arterial vasodilation to working muscles, vaso

constriction to nonworking muscles, and dilat

ing pupils and bronchi. Under acute stress, parasympathetic nervous system

– regulated activities subside (e.g., salivary and intestinal secretions for digestion and nutrient absorp

tion, growth and repair). Frequent sympa

thetic nervous system dominance under repeated acute stress may interfere with growth and repair, especially important for children’s development, and suggests one pathway through which childhood stress may shape lifelong health and susceptibility. Chronic stress, immune function, and inflammatory response. Chronic stress may be characterized by recurrent acute stress or an inability to moderate acute stress responsesStress and air pollution susceptibility

Environmental Health Perspectives • volume 117 | number 9 | September 2009 

### 1353 (McEwen and Seeman 1999). Building on Hans Selye’s model of nonspecific suscepti

bility and allostatic load models of cumula

tive wear and tear, attention is increasingly being directed toward identifying biological mediators linking chronic stress to immune and endocrine function (Miller et al. 2002; Segerstrom and Miller 2004). Chronic stress and associated negative emotional states (e.g., depression, anxiety, anger) may mediate immune and endocrine processes (Kiecolt-Glaser et al. 2002), with associations so consistent that some research

ers have proposed reconceptualizing depres

sion as dysfunction in HPA-axis regulation and stress response (Sternberg et al. 1992). Endocrine responses to chronic stress include dysregulation in production of catecholamines (epinephrine, norepinephrine), adrenocor

ticotropin, cortisol, growth hormone, and prolactin. Cytokines, particularly IL

- 6, stimulate corticotrophin-releasing hormone and HPA-axis activity, increasing plasma adrenocorticotropin hormone and cortisol (Hellhammer et al. 1997; Kirschbaum et al. 1995; Ockenfels et al. 1995; Seeman et al. 1997). Frequent activation of the glucocortiglucocorti coid receptor by cortisol can lead to blunted glucocorticoid response (Miller et al. 2002), increased nuclear factor- κ B signaling (Miller

et al. 2008), and dysregulated catecholamine production (Glaser and Kiecolt-Glaser 2005). Immune-linked inflammatory response may infleunce asthma and related airway disease

. Asthma -linked parameters responsive to stress include IgE (Wright et al. 2004) and cytokine production (Chen et al. 2003) and respiratory inflammation (Umetsu et al. 2002). Early life chronic stress may alter T-helper ( Th ) 1–Th2 immune cell balance (Umetsu et al. 2002), which is linked with childhood asthma, allergy, and inflammatory responses (Miller and Chen 2007). Impacts on common physiologic systems. Growing evidence suggest s complex dosedependent interactions among multiple pollu

tants (Mauderly and Samet 2009), mediated through the same mechanistic pathway

, or some pollutants may potentiate effects of others. Similarly, stress may potentiate pollu

tion health effects through immune and inflammatory processes, or stress and pollution may affect common physiologic systems. Both early childhood environmental exposures and stress-related catecholamines affect Th1–Th2 balance (Umetsu et al. 2002). Psychological stress (Epel et al. 2004), poly cyclic aromatic hydrocarbons, cigarette smoke (Adcock and Ito 2005), and ozone (Fugisawa 2005) affect oxidative stress, which is linked to asthma and COPD (Rahman and MacNee 2000). Both stress and diesel exhaust particles are associated with elevated cytokines (e.g., IL-2, IL-6, and local IgE in nasal mucosa) (Diaz-Sanchez et al. 2000; Nel 2001). Some evidence suggests that stress may alter permeability of bodily mem

branes to chemical exposures

, such that s tress may alter systemic transport and chemical uptake into organs including the brain (Sinton

et al. 2000), facilitating combined and syn

ergistic effects of stressors and pollution on many bodily systems. 

### Key Issues to be Addressed as This Work Progresses Careful attention to stress measurement. For environmental researchers, social epidemio

logic theory and methods for stress meas

urement may be unfamiliar, but accurately understanding and applying these principles is necessary to produce meaningful analyses of interactions among stressors and pollution exposures. Careful attention to stress processes and distinction among the major components is needed to accurately capture and interpret stress effects on susceptibility. Moreover, because perceived stress is highly variable over time, it is important that measured stress peri

ods are temporally appropriate to the pollu

tion exposures and outcomes under study. The stress process is often described in three phases: a ) the stressor (i.e., any event, condi

tion, or external stimuli posing a physical or psychological challenge), b ) stress appraisal (i.e., how one experiences, perceives, or inter

prets the event), and c ) stress response (e.g., psychological and physiologic sequelae). These phases are interdependent. A stres

sor appraised as benign or beneficial, rather than threatening, generally produces no stress response. Highly thorough stress assessments would measure each stage, which is rarely fea

sible

. Most studies focus on a single

, chronic stressor (e.g., caregiver burden) or one unlikely to be positively appraised (e.g., exposure to violence, natural disaster). Newer measures emphasize later stages of the stress process. Because of inconsistent findings with stressor measures (e.g., life event scales assessing major life changes) (Dohrenwend et al. 1993), more researchers today use perceived stress measures, which capture response to multiple stressors (Cohen et al. 1983, 1995). Recent evidence indicates, however, that subjective stress may poorly predict immune change (Segerstrom and Miller 2004); thus, another approach emphasizes negative affect (e.g., anxiety, depression) as a cumulative indicator of men

tal distress and psychosocial stress. Negative affect may serve as a common final pathway for multiple psychological stressors, possibly providing a more stable indicator of cumula

tive stress and susceptibility (Kubzansky et al. 2000; Seeman et al. 2002). Other approaches include using bio

markers—hormones or immune markers associated with physiological stress responses, including glucocorticoids or cytokines (Miller et al. 2002). Although many physiologic sys

tems are influenced by acute and chronic stress, there is relatively little consensus on optimal biomarkers to capture physiologic changes with acute or chronic stress. Formerly, corti

costeroids (e.g., cortisol) in blood or saliva were emphasized as markers of HPA-axis activity, although stress-related HPA function changes lead to cortisol dysregulation (via glucorticoid resistance and HPA regulation), not simply increased cortisol production. Thus, cortisol can be difficult to interpret and better indi

cates acute rather than chronic stress. Recent research emphasizes indicators of glucocorti

coid resistance and neuroendocrine signaling (Miller et al. 2008). Other evidence suggests that C-reactive protein (Miller G, personal communication) and tumor necrosis factor

- α (Clougherty JE, Rossi CA, Lawrence J, Long M, Diaz E, Koutrakis P, et al., unpub

lished data) may capture chronic stress in rats. Although no single biomarker is appropriate for all applications (Brunner 2007), suites of physiologic parameters have been developed to represent allostatic load in humans, includ

ing indicators of cardiovascular function, metabolism, cholesterol, glucose metabolism, HPA-axis function, and sympathetic nervous system activity (Kubzansky et al. 2000; Seeman and Singer 2002). Several studies document chronic stress effects on cardiovascular risk indicators (abdominal obesity, elevated serum triglycerides , low high-density lipoprotein cho

lesterol, glucose intolerance, elevated blood pressure) (Brunner et al. 1997), known collec

tively as metabolic syndrome, and may provide a method for capturing cumulative stress effects on cardiovascular and systemic function. Relative temporality in stress and pollu

tion exposures. Generally, stressors must pre

cede or be contemporaneous with pollution exposures to plausibly modify their effects. The actual periods of stress and pollution expo

sures, their overlap, and temporal relation to health outcomes, deserve careful attention, because temporal exposure misclassification may nullify or even reverse the directionality of observed interactions. For example, if stress
exposure occurs after or very late in a pollu

tion exposure interval, interpreting observed interactions is problematic. If perceived stress is stable over time, the report will accurately reflect stress during the hypothesized period of susceptibility. If perceived stress varies over the period, however, and respondents com

pare current stress to prior experiences, then individuals reporting high stress likely experi

enced relatively lower stress previously, during the pollution exposure period. Such temporal misclassification may significantly confound results, and researchers should ensure that stress and pollution measurement periods support a plausible physiologic interaction in relation to the health outcome of interest.Clougherty and Kubzansky



### 1354 volume 117 | number 9 | September 2009 • Environmental Health Perspectives Spatial correlations among social and physical exposures. Both social and physicalexposures vary across communities, and lowerincome and minority communities may be disproportionately exposed to both (Evans and English 2002; Lupien et al. 2001; MorelloFrosch and Shenassa 2006). Strong spatial covariance among stress, SES, and pollution has confounded geographic information sys

tems (GIS)–based air pollution epidemiology, and spatial epidemiologists are challenged to differentiate health effects of traffic-related pol

lution from those of spatially correlated noise, stress, or poverty. Evidence suggests that road

way noise, a spatial stressor correlated with pollution, increases heart rate among adults and children (Belojevic et al. 2008; Belojevic and Saric-Tanaskovic 2002), and living in high-traffic areas predicts higher stress, lower self-reported health, and depressive symptoms (Gee and Takeuchi 2004), effects distinct from those of pollution per se. Because of spatial autocorrelation and pos

sible confounding, accurate fine-scale expo

sure assessment for both stress and pollution is critical. GIS-based exposure models, now common in environmental epidemiology, should be validated to the spatial extent of the cohort examined, and spatial patterns in stres

sors and pollution, at multiple levels, should be carefully considered to avoid spatial mis

classification and confounding. Social–physical correlations may vary by region or context, and the appropriate geographic scale of analy

sis may vary as well . Th e 1995–1997 Health Survey for England found that in urban areas, lower-SES households experienced worse air quality, al though the opposite was true in rural regions. Air quality and SES independently predicted lung function in both settings, withgreater pollution susceptibility among lowerSES men, but not women (Wheeler and BenShlomo 2005). Although some neighborhoods may expe

rience higher average levels of pollution and stressors (variation across neighborhoods), one should not assume that individuals or resi

dences within these neighborhoods are rela

tively more exposed to both (variation within neighborhoods). Individuals living closer to highways likely have higher pollution expo

sures than do other community residents but are not necessarily more exposed to violence or family stress. Similarly, U.S. census tracts, selected to be relatively homogeneous for key sociodemographic indicators, may be a mean

ingful unit of analysis for some social and eco

nomic factors (Subramanian et al. 2005). All persons within a census tract, however, do not have similar traffic-related pollution exposures, which vary dramatically within 50

– 200 m of major roadways (Zhu et al. 2002). Nonlinear, threshold, and saturation effects. There is evidence linking stress and air pollution, separately, to asthma onset and exacerbation. Because both exposures inde

pendently influence respiratory health, we might expect that with especially high levels of either exposure, exacerbations likely occur, regardless of the second exposure. Effectively, very high exposures may overpower any potential interaction effects. Potential saturation effects call for careful attention to the exposure range observed in any study, relative to normal exposure lev

els, to inform whether interactions should be expected and how to interpret observed interactions. For example, our group reported that asthmatic children of families reporting higher fear of violence showed less symptom improvement with allergen-reducing indoor environmental interventions (Clougherty

et al. 2006). Counter to initial hypotheses, this result suggested saturation effects in our very high-exposure public housing cohort. Either fear of violence or allergen exposures may have been high enough to independently induce or maintain symptoms. The need for toxicologic research. Because of strong potential confounding between stressors and pollution, epidemiologic methods alone are unlikely to fully differentiate their effects or resolve spatial confounding. Additionally, chronic air pollution exposure may contrib

ute to HPA

- axis stimulation and stress pro

cesses (Sirivelu et al. 2006). Thus, experimental studies using well-developed animal models of social stress (e.g.

, monkeys, rats) are needed to delineate these effects. Toxicologic data can improve causal inference and interpretability by randomizing exposures, controlling their temporality and intensity, and, importantly, can help elucidate physiologic mechanisms for stress-pollution interactions. Several authors have investigated stress as a modifier of neurologic effects of lead in ani

mal models. Cory-Slechta et al. (2004) exam

ined separate and combined effects of restraint stress and lead in pregnant dams on corticos

terone, neurotransmitter levels, and behavioral learning. They found significant interactions, generally more prominent in female offspring, and noted that lead alone influenced corti

costerone, suggesting that lead may influ

ence later- life susceptibility (Virgolini et al. 2005, 2006). They observed strongly altered HPA

- axis function with both lead and stress, separately and in combination, providing a model for better understanding the etiology of conditions linked to both exposures and potentially mediated through HPA function, including obesity, hypertension, diabetes, anxiety, schizophrenia

, and depression (RossiGeorge et al. 2009). We recently compared short-term respira

tory response to concentrated fine particu

late air pollution (CAPs) among chronically stressed and unstressed rats. Using the social dominance paradigm, a rat model of social stress (Hotsenpiller and Williams 1996; Luciano and Lore 1975), we introduced male

test rats individually into the cage of an older, larger male, over an 8- week period, to estab

lish chronic stress conditions. Test animals were exposed to controlled CAPs for 5 hr on days after stress exposures. Across four expo

sure groups [stress/CAPs; stress/filtered air (FA); nonstress/CAPs; nonstress/FA], ani

mals exposed to both stress and CAPs dis

played elevated C-reactive protein and altered respiratory function relative to other groups, with higher frequencies and briefer pauses after inspiration and expiration, suggesting a shallower, more rapid breathing pattern (Clougherty et al. 2008). Experimental studies involving humans. Experimental studies have identified physio

logic parameters associated with stressors in humans (exam stress, public speaking). Although these studies can examine only shortterm, relatively benign stressors, they do allow for controlled, randomized stressor exposures that are not feasible in the community set

ting. Fiedler et al. (2005) examined combined effects of stressors (public speaking, math chal

lenge) and oxidation by-products of indoor volatile organic carbons and ozone, prevalent in office settings, on cortisol, respiratory func

tion, and symptoms (anxiety, eye/nose irrita

tion, respiratory symptoms) at multiple time points. They found that stress predicted anxi

ety symptoms and cortisol, outweighing any potential interaction with pollution (Fiedler

et al. 2005). Such experimental studies can

not mimic the lifelong stress and pollution exposures associated with low SES but help to elucidate some mechanisms for stress-related susceptibility and, importantly, allow for the separation of persistently correlated exposures, otherwise difficult to delineate

. Pollution and pollution sources as psycho

social stressors. Health geographers influenced by the environmental justice movement have long understood that neighborhood pol

lution sources

, including highways, power plants, and smokestacks, can send strong messages to residents about the value of their health and well-being to the larger society (Bullard 1990). Indeed, the study of air pol

lution effects on health has historically con

sidered its psychological effects (Colligan 1981; Strahilevitz et al. 1979), including psychosocial impacts of perceived exposure (Rotton et al. 1979) on vigilance (Horvath and Dahms 1971; Putz et al. 1977), test per

formance (Hore and Gibson 1968), irritation (Jones 1978), aggression (Rotton et al. 1979), behavior (Evans and Jacobs 1981), neurologic effects (Hore and Gibson 1968), and vision impairment (Lagerwerff 1963). More recent evidence indicates that air quality below regulatory guidelines can be detected byStress and air pollution susceptibility

Environmental Health Perspectives • volume 117 | number 9 | September 2009 

### 1355 residents, with negative health consequences (Forsberg et al. 1997), although perceived air quality can also be influenced by disease status (Piro et al. 2008). Indeed, it can be dif

ficult to distinguish health effects produced by the physical aspects of air pollution from its psychosocial health effects in communities near toxic sites (Elliot et al. 1993; Eyles et al. 1993), to separate both pollution-derived effects from those of other spatially correlated stressors, or to establish directionality. To better elucidate this complex synergy among exposure pathways, environmental expo

sure assessment and risk management may ultimately consider both tangible physical and psychosocial effects of pollution to fully understand the mechanisms linking air pollu

tion, stress, and susceptibility.


### Additional Questions to be Explored Many questions about stress-related pollution susceptibility remain . We raise several here, describing each only briefly, and hope these issues will be explored in detail in coming years. To which pollutants and health out

comes is stress-related susceptibility relevant?A few studies demonstrate significant stressrelated modification in air pollution effects on respiratory health, particularly asthma onset (Clougherty et al. 2007) and exacer

bation (Chen et al. 2008; Clougherty et al. 2006). Stress may also modify relationships between bone lead and cardiovascular out

comes (e.g., hypertension) (Peters et al. 2007) and, in the same data set, heart rate variabil

ity (Clougherty JE, Peters JL, Schwartz J, Kubzansky L, unpublished data). A growing toxicology literature demonstrates stress-re

lated susceptibilities to neurocognitive effects of lead and polychlorinated biphenyls, includ

ing neurologic damage and hippocampal func

tion (Cory-Slechta et al. 2004). These vastly different exposures and outcomes demonstrat

ing stress–pollutant interactions and the many physiologic systems affected by stress (e.g., sympathetic regulation, immune function, glucocorticoid production) suggest potential stress-related modifications in a wide range of pollutant exposures on health outcomes. Are these interactions different in illness onset than in exacerbation? For preexisting illness, many factors may modify stress effects on illness severity and chronicity, including current medical treatment and comorbidi

ties. The progression of preexisting illness, if influenced by stress, may also change the relevant temporalities, as later stress could plausibly modify recovery from environmen

tally derived illness. Thus, stress–pollution interactions may be even more complicated for existing illness, and careful attention to temporality and confounding (e.g., by medi

cal treatment) is even more important. Some evidence suggests that stress may modify pollution effects in exacerbating preexisting asthma (Chen et al. 2008; Clougherty et al. 2006), al though both studies produced associ

ations opposite to hypotheses (stronger pollu

tion effects with lower stress). More generally, attention to distinguishing processes related to illness onset from illness progression or exac

erbation will be critical in assessing whether interactions are robust or should be expected in healthy populations. Are there critical periods for stress and pollution exposures across the life course? Different diseases are relevant at different life stages

. Asthma is among the most preva

lent chronic illnesses of childhood, whereas cardiovascular illness generally afflicts older persons. Because the life

- course distribution of illness varies considerably, relationships among stress, susceptibility, and illness likely also vary with age. Although stress can be toxic at any age, there may be critical periods, such as during early immune development, when it is particularly influential in shaping future susceptibility and disease risk (Evans and English 2002). Parental stress has been used to exam

ine stress exposures in young children, and research supports inverse associations for both mother’s SES and depressive states on chil

dren’s stress hormone levels (Lupien et al. 2000). Prospective studies have linked care

giver stress to infant wheeze (Wright et al. 2002), and maternal stress during pregnancy may influence immune function and health in neonates (Weiss and Bellinger 2006). Maternal air pollution exposures associated with low birth weight (Gouveia et al. 2004) may increase later childhood respiratory dis

ease risk. Stress exposures during development may produce broad biological and psychologi

cal vulnerabilities, affecting neuroendocrine, immune, metabolic, and growth processes (Viltart and Vanbesien-Maillot 2007)

. Although not entirely immutable, these effects may have permanent and compounding con

sequences, especially if not addressed early (Cicchetti and Walker 2001; McEwen 2008). What are the roles of gender/sex and race/ ethnicity in shaping stress-related susceptibil

ity to pollution? It is beyond the scope of this review to describe the myriad societal-level sources of stress. However, ongoing research in this area will be informed by the growing literatures on racism as a prevalent stressor, and on sex and gender differences in psycho

logical and physiologic responses to stress and susceptibility. Racial and ethnic minority groups in the United States are often differentially exposed to psychosocial stressors and physi

cal contaminants in their homes, neighbor

hoods, and workplaces (Bullard 1990). The environmental justice movement has drawn attention to disproportionate pollution expo

sures in minority and low-income commu

nities (Krieger 1990), but only recently has attention been directed to combined pollu

tion exposures and greater susceptibility in these communities (Clougherty et al. 2007; Evans and English 2002; Morello-Frosch and Shenassa 2006; National Environmental Justice Advisory Council 2004). Experiences of racism as a stressor have been associated with negative physical and emotional health effects (Borrell et al. 2006; Clark et al. 1999; Krieger and Sidney 1996; Kwate et al. 2003; Landrine and Klonoff 1996; Thompson 1996) modified by coping practices and social support (Kwate

et al. 2003). Experiences of racial discrimina

tion predicted poorer birth outcomes among women with Arabic names in California after 11 September 2001 (Lauderdale 2006). There is also evidence of poorer health, including mortality, for U.S. persons than for foreignborn persons of the same ethnicity, especially Hispanics (Singh and Hiatt 2006). Effects of race and racism are not fully mediated through social class (Kwate et al. 2003) and are not gen

erally attributable to genetic variation (Krieger 2005). Race-related stressors may contribute to “weathering” or physiologic wear and tear (Geronimus 1992; Goodman et al. 2005; Merritt et al. 2004). Hypertension onset, for example, may be four to seven times higher among low-SES than amonghigh-SES AfricanAmerican men (James et al. 2006). African Americans also have higher rates of cardiovas

cular illness (Pappas et al. 1993) and low birth weight (David and Collins 1997) relative to Caucasians with comparable education. Sex and gender differences in stress and susceptibility may be significant. The distinction between gender (socially influ

enced behaviors) and sex (biology, includ

ing hormonal composition, sex organs, and anthropometric measures) is comparable with that between exposure and susceptibil

ity. Sex differences have been observed in air pollution–health associations

. After early childhood, more studies report greater risks among women and girls (Luginaah et al. 2005; Oftedal et al. 2008; Rojas-Martinez

et al. 2007; Rosenlund et al. 2008), possi

bly explained, in part, by biological sex dif

ferences in lung capacity, hormonal status, inflammation, or airway particle deposition (Kim and Hu 1998; Kohlhaufl et al. 1999). Gendered social and behavioral patterns also matter. Sex stratification in the workforce and work-related exposures are well documented (Arbuckle 2006; Messing and Stellman 2006). Among children, play activities may influ

ence ventilation rate, creating exposure dif

ferences between boys and girls (McConnell

et al. 2002). Common pollution exposures metrics may be differently accurate by gen

der ; residential exposures may better captureClougherty and Kubzansky



### 1356 volume 117 | number 9 | September 2009 • Environmental Health Perspectives exposures for stay-at-home parents (usually mothers) than for working adults (Dietrich

et al. 2008; Jedrychowski and Krzyzanowski 1989). Physiologic stress responses differ by sex (Sundaram et al. 2004; Taylor et al. 2000), as does observed effect modification by SES (Wheeler and Ben-Shlomo 2005), such that gendered stress assessment may be needed to fully understand stress-linked effect modification for air pollution. To what extent are the effects of SES attributable to stress? As described, there is growing evidence of SES effect modifica

tion in the air pollution–disease relationship

. ACS studies reported stronger health effects of air pollution among less- educated adults (Krewski et al. 2000), and time-series studies report the same (Jerrett et al. 2004; Kan et al. 2008; Lin et al. 2004; Martins et al. 2004), al though these air pollution studies have not identified causal components of SES shap

ing susceptibility. Like air pollution, SES is a complex exposure mix accumulated over the life course, potentially including poorerquality education ; nutrition ; housing ; health

care ; health behaviors ; pollution exposures in the home, community, and workplace ; per
ceived social position ; and other stressors. Indeed, newer variants of the allostatic load model incorporate primary (e.g., perceived stress, psychological response) and secondary (e.g., smoking, sleep, dietary behaviors) mani

festations of stress (McEwen 2006). Growing evidence links low SES to perceived stress and distress (Adler et al. 1994; Miller and Chen 2007) and to biological markers of stress-re

lated susceptibility (Lupien et al. 2001). Some of these studies used allostatic load models to link SES to distress and markers of disease risk (e.g., metabolic dys regulation) (Kubzansky

et al. 2000). Other studies link allostatic load parameters to morbidity and mortality, sug

gesting that allostatic load may mediate rela

tionships between SES and mortality, after accounting for demographic characteristics and physician-diagnosed illness (Seeman et al. 2004). Among children, low SES may be a marker of early exposure to adversity

. Recent studies link low childhood SES to epigenetic changes in messenger ribonucleic acid (mRNA) for the glucocorticoid receptor and toll-like recep

tor 4

, indicative of proinflammatory profiles associated with asthma and allergic illness (Miller and Chen 2007). Low-SES children 6–10 years of age have shown higher basal cor

tisol levels than higher-SES children (Lupien

et al. 2001). Children of parents reporting higher stress display physiologic hyperrespon

siveness, and low-income children of depressed mothers show sex-specific physiologic responses: elevated cortisol in girls, HPA

- axis hypoactivity in boys (Fernald et al. 2008). Children of depressed mothers can display altered adrenocorticotropic hormone and corticotropin-releasing hormone production into young adulthood (Ronsaville et al. 2006). Evidence suggesting that stress is a key media

tor for SES effects on health is not universally endorsed, and associations between SES and stress-related biological changes are not always positive (Dowd and Goldman 2006). Authors have argued that psychosocial factors are inex

tricably bound to material factors in developed countries ; therefore, the accumulated evidence does not unequivocally demonstrate an inde

pendent pathway by which psychosocial stress may link SES to physical health (Macleod and Davey Smith 2003). Other aspects of SES (e.g., nutrition, health care) may also influ

ence pollution susceptibility, and methods are needed to determine their effects. We believe that the evidence to date is broadly suggestive of a link between SES and physiologic suscep

tibility, a significant portion of which may be explained by life stress. Continued research in this area is valuable, especially as it improves our understanding of the pathways through which physical exposures, including pollu

tion, may differently impinge on the health of vulnerable populations.


### Conclusions There is tremendous potential, although much work still to be done, in understanding com

bined effects of social and physical environ

mental exposures. These topics are exceedingly complicated

. Accurately characterizing both social and physical exposures is a significant challenge that must be performed carefully, especially in light of potential confounding across the exposures of interest, before analyz

ing and interpreting interactions. The issues we have highlighted here— temporal relationships between stressors and pollution; nonlinearity and saturation effects; spatial colinearity across exposures; age-related susceptibility and critical periods; and dis

tinctions between processes related to illness etiology and exacerbation—will be critical in exploring social–environmental interactions. These factors are significant enough to distort observed associations (e.g., saturation effects may reverse interactions at high exposures; treatment can mask exacerbations of pre-exist

ing illness). With sustained attention to these issues, we can work toward a clearer, richer understanding of complex effects among social and physical environmental exposures on health.

**R efe**  **r ences** 

Adcock IM, Ito K. 2005. Glucocorticoid pathways in chronic obstructive pulmonary disease therapy. Proc Am Thorac Soc 2(4):313–319. Adler N, Matthews K. 1994. Health psychology: why do some people get sick and some stay well? Annu Rev Psychol 45:229–259. Adler NE, Boyce T, Chesney MA, Cohen S, Folkman S, Kahn RL, et al. 1994.

� lenge of the gradient. Am Psychol 49(1):15–24. Arbuckle TE. 2006. Are there sex and gender differences in acute exposure to chemicals in the same setting? Environ Res 101:195–204. Belojevic G, Jakovljevic B, Stojanov V, Paunovic K, Ilic J. 2008. Urban road

- traffic noise and blood pressure and heart rate in preschool children. Environ Int 34:226–231. Belojevic G, Saric

- Tanaskovic M. 2002. Prevalence of arterial hypertension and myocardial infarction in relation to subjec

� tive ratings of traffic noise exposure. Noise Health 4:33–37. Borrell LN, Kiefe CI, Williams DR, Diez

- Roux AV, Gordon

Larsen P. 2006. Self

- reported health, perceived racial discrimination, and skin color in African Americans in the CARDIA study. Soc Sci Med 63:1415–1427. Brunner E. 2007. Biology and health inequality. PLoS Biol 5(11):2449–2452. Brunner EJ, Marmot MG, Nanchahal K, Shipley M, Stansfeld SA. 1997. Social inequality in coronary risk: central obesity and the metabolic syndrome. Evidence from the Whitehall II study. Diabetologia 30:1341–1349. Bullard R. 1990. Dumping in Dixie: Race, Class, and Environmental Quality. Boulder, CO:Westview Press

. Chen E, Fisher EB, Bacharier LB, Strunk RC. 2003. Socioeconomic status, stress, and immune markers in adolescents with asthma. Psychosom Med 65(6):984–992. Chen E, Schreier HMC, Strunk R, Brauer M. 2008. Chronic traffic

- related air pollution and stress interact to predict biological and clinical outcomes in asthma. Environ Health Perspect 116:970–975

. Cicchetti D, Walker EF. 2001. Stress and development: bio

� logical and psychological consequences [Editorial]. Dev Psychopathol ogy 13:413–418. Clark R, Anderson NB, Clark VR, Williams DR. 1999. Racism as a stressor for African Americans: a biopsychosocial model. Am Psychol 54(10):805–816. Clougherty JE, Levy JI, Hynes HP, Spengler JD. 2006. A longitu

� dinal analysis of the efficacy of environmental interventions on asthma

- related quality of life and symptoms among chil

� dren in urban public housing. J Asthma 43:335–343. Clougherty JE, Levy JI, Kubzansky LD, Ryan PB, Suglia SF, Canner MJ, et al. 2007. Synergistic effects of traffic

related air pollution and exposure to violence on urban asthma etiology. Environ Health Perspect 115:1140–1146. Clougherty JE, Rossi CA, Lawrence J, Long M, Diaz E, Koutrakis P, et al. 2008 Social stress and susceptibility to concentrated particulate air pollution (CAPs) in rats [Abstract]. Epidemiology 19(6):S163. Cohen S, Kamarack T, Mermelstein R. 1983. A global measure of perceived stress. J Health Soc Behav 24(4):385–396. Cohen S, Kessler RC, Underwood GL. 1995. Measuring Stress: A Guide for Health and Social Scientists. New York:Oxford University Press. Colligan MJ. 1981. The psychological effects of air pollution. Bull NY Acad Med 57(10):1014–1026. Cory

- Slechta DA, Virgolini MB, Thiruchelvam M, Weston DD, Bauter MR. 2004. Maternal stress modulates the effects of developmental lead exposure. Environ Health Perspect 112:717–730. David RJ, Collins JW. 1997. Differing birth weight among infants of U.S.

- born blacks, African

- born blacks, and U.S.

- born whites. N Engl J Med 337:1209–1214. deFur PL, Evans GW, Cohen Hubal EA, Kyle AD, Morello

Frosch RA, Williams DR. 2007. Vulnerability as a function of individual and group resources in cumulative risk assess

� ment. Environ Health Perspect 115:817–824. Diaz

- Sanchez D, Penichet

- Garcia M, Saxon A. 2000. Diesel exhaust particles directly induce activated mast cells to degranulate and increase histamine levels and symptom severity. J Allergy Clin Immunol 106:1140–1146. Dietrich DF, Gemperil A, Gaspoz J

- M, Schindler C, Liu SL

- J, Gold DR, et al. 2008. Differences in heart rate variabil

� ity associated with long

- term exposure to NO 2 . Environ Health Perspect 116:1357–1361. Dockery D. 1993. An association between air pollution and mor

� tality in six U.S. cities. N Engl J Med 329:1753–1759. Dohrenwend BP, Raphael KG, Schwartz S, Stueve A, Skodol A. 1993. The structured event probe and narrative rating method for measuring stressful life events. In: Handbook of Stress (L. Goldberger L, Breznitz S, eds). New York:Free Press, 174–199. Dowd J, Goldman N. 2006. Do biomarkers of stress mediate the relation between socioeconomic status and health? J Epidemiol Community Health 60:633–639.Stress and air pollution susceptibility

Environmental Health Perspectives • volume 117 | number 9 | September 2009 

### 1357 Elliot SJ, Taylor SM, Walter S. 1993. Modelling psychosocial effects of exposure to solid waste facilities. Soc Sci Med 37(6):791–804. Epel E, Blackburn E, Lin J, Dhabhar F, Adler N, Morrow J, et al. 2004. Accelerated telomere shortening in response to life stress. Proc Natl Acad Sci USA 101(49):17312–17315. Evans GW, English K. 2002. The environment of poverty: mul

� tiple stressor exposure, psychophysiological stress, and socioemotional adjustment. Child Dev 73(4):1238–1248. Evans GW, Jacobs SV. 1981. Air pollution and human behavior. J Soc Issues 37:95–125. Eyles J, Taylor SM, Johnson N. 1993. Worrying about waste: living close to solid waste disposal facilities in southern Ontario. Soc Sci Med 37(6):805–812. Fernald LCH, Burke HM, Gunnar MR. 2008. Salivary cortisol lev

� els in children of low

- income women with high depressive symptomatology. Dev Psychopathol 20:423–436. Fiedler N, Laumbach R, Kelly

- McNeil K, Lioy P, Fan Z, Zhang J,
et al. 2005. Health effects of a mixture of indoor air vola

� tile organics, their ozone oxidation products, and stress. Environ Health Perspect 113:1542–1548. Finkelstein M, Jerrett M, DeLuca P, Finkelstein N, Verma D, Chapman K, et al. 2003. Relation between income, air pollution, and mortality: a cohort study. Can Med Assoc J 169(5):397–402. Forsberg B, Stjernberg N, Wall S. 1997. People can detect poor air quality well below guideline concentrations: a preva

� lence study of annoyance reactions and air pollution from traffic. Occup Environ Med 54(1):44–48. Fugisawa T. 2005. Role of oxygen radicals on bronchial asthma. Curr Drug Targets Inflamm Allergy 4(4):505–509. Gee G, Payne

- Sturges D. 2004. Environmental health disparities: a framework for integrating psychosocial and environmen

� tal concepts. Environ Health Perspect 112:1645–1653. Gee GC, Takeuchi DT. 2004. Traffic stress, vehicular bur

� den, and well

- being: a multilevel analysis. Soc Sci Med 59(2):405–414. Geronimus A. 1992. The weathering hypothesis and the health of African

- American women and infants: evidence and speculations. Ethn Dis 2:207–221. Glaser R, Kiecolt

- Glaser JK. 2005. Stress

- induced immune dys

� function: implications for health. Nat Immunol 5:243–251. Goodman E, McEwen BS, Dolan LM, Schafer

- Kalkoff T, Adler NE. 2005. Social disadvantage and adolescent stress. J Adolesc Health 37:484–492. Gouveia N, Bremner S, Novaes M. 2004. Association between ambient air pollution and birth weight in São Paulo, Brazil. J Epidemiol Community Health 58:11–17. Graves P. 1988. The robustness of hedonic price estimation: urban air quality. Land Econ 64:220–233. Hellhammer DH, Buchtal J, Gutberlet I, Kirschbaum C. 1997. Social hierarchy and adrenocortical reactivity in men. Psychoneuroendocrinology 22:643–650. Hiltermann T, Bruijne Cd, Stolk J, Zwinderman A, Spieksma F, Roemer W, et al. 1997. Effects of photochemical air pol

� lution and allergen exposure on upper respiratory tract inflammation in asthmatics. Am J Respir Crit Care Med 156(6):1765–1772. Hoek G, Brunekreef B, Goldbohm S, Fischer P, van den Brandt P. 2002.

� tors of traffic

- related air pollution in the Netherlands: a cohort study. Lancet 360:1203–1209. Hore T, Gibson DE. 1968. Ozone exposure and intelligence
tests. Arch Environ Health 17:77–79. Horvath SV, Dahms TE. 1971. Carbon monoxide and human vigilance: a deleterious effect of present urban concentra

� tions. Arch Environ Health 23:343–347. Hotsenpiller G, Williams J. 1996. Conditioned fear and anal

� gesia to conspecific odors: benzodiazepine and 5

- HT1A agonists. Psychobiology 24(2):118–126. James SA, Van Hoewyk J, Belli RF, Strogatz DS, Williams DR, Raghunathan TE. 2006. Life

- course socioeconomic posi

� tion and hypertension in African

- American men: The Pitt County Study. Am J Public Health 96(5):812–817. Jang A, Yeum C, Son M. 2003. Epidemiologic evidence of a relationship between airway hyperresponsiveness and exposure to polluted air. Allergy 58(7):585–588. Jedrychowski W, Krzyzanowski M. 1989. Ventilatory lung func

� tion and chronic chest symptoms among the inhabitants of urban areas with various levels of acid aerosols: prospec

� tive study in Cracow. Environ Health Perspect 79:101–107. Jerrett M, Burnett R, Brook J, Kanaraglou P, Giovis C, Finkelstein J, et al. 2004. Do socioeconomic char

� acteristics modify the short term association between air pollution and mortality? Evidence from a zonal time series in Hamilton, Canada. J Epidemiol Community Health 58:31–40. Jones JW. 1978. Adverse emotional reactions of nonsmokers to secondary cigarette smoke. Environ Psychol Nonverbal Behav 3:125–127. Kan H, London SJ, Chen G, Zhang Y, Song G, Zhao N, et al. 2008. Season, sex, age, and education as modifiers of the effects of outdoor air pollution on daily mortality in Shanghai, China: The Public Health and Air Pollution in Asia (PAPA) Study. Environ Health Perspect 116:1183–1188. Kiecolt

- Glaser J, McGuire L, Robles T, Glaser R. 2002. Emotions, morbidity, and mortality: new perspectives from psycho

� neuroimmunology. Annu Rev Psychol 53:83–107. Kim CS, Hu SC. 1998. Regional deposition of inhaled particles in human lungs: comparison between men and women. J Appl Physiol 84(6):1834–1844. Kirschbaum C, Prussner JC, Stone AA, Federenko I, Gaab J, Lintz D, et al. 1995. Persistent high cortisol responses to repeated psychological stress in a subordinate population of healthy men. Psychosom Med 57:468–474. Kohlhaufl M, Brand P, Scheuch G, Meyer TS, Schulz H, Haussinger K. 1999. Increased fine particle deposition in women with asymptomatic nonspecific airway hyper

� responsiveness. Am J Respir Crit Care Med 159(3):902–906. Krewski D, Burnett RT, Goldberg MS, Hoover K, Siemiatycki J, Jerrett M, et al. 2000. Reanalysis of the Harvard Six Cities Study and the American Cancer Society Study of Particulate Air Pollution and Mortality. Cambridge, MA:Health Effects Institute. Krieger N. 1990. Gender and racial discrimination: risk factors for high blood pressure? Soc Sci Med 12:1273–1281. Krieger N. 2005. Stormy weather: race, gene expression, and the science of health disparities. Am J Public Health 95(12):2155–2160. Krieger N, Sidney S. 1996. Racial discrimination and blood pressure: the CARDIA Study of young black and white adults. Am J Public Health 86:1370–1378. Kubzansky LD, Kawachi I, Sparrow D. 2000. Socioeconomic status, hostility, and risk factor clustering in the Normative Aging Study: any help from the concept of allostatic load? Ann Behav Med 21(4):330–338. Kubzansky LD, Wright RJ, Cohen S, Weiss ST, Rosner B, Sparrow D. 2002. Breathing easy: a prospective study of optimism and pulmonary function in the Normative Aging Study. Ann Behav Med 24(4):345–353. Kwate NOA, Valdimarsdottir HB, Guevarra JS, Bovbjerg DH. 2003. Experiences of racist events are associated with negative health consequences for African American women. J Natl Med Assoc 95(6):450–460. Lagerwerff JM. 1963. Prolonged ozone inhalation and its effect on visual parameters. Aerosp Med 34:479–486. Landrine H, Klonoff EA. 1996. The Schedule of Racist Events: a measure of racial discrimination and a study of its nega

� tive physical and mental health consequences. J Black Psychol 22:144–168. Lanki T, de Hartog JJ, Heinrich J, Hoek G, Janssen NA, Peters A, et al. 2006.

� Can we identify sources of fine par ticles responsible for exercise

- induced ischemia on days with elevated air pollution? The ULTRA study. Environ Health Perspect 114:655–660. Lauderdale DS. 2006. Birth outcomes for Arabic

- named women in California before and after September 11. Demography 43(1):185–201. Lin M, Chen Y, Villeneuve P, Burnett R, Lemyre L, Hertzman C,
et al. 2004.

� tion of children with low household income in Vancouver, British Columbia, Canada. Am J Epidemiol 159(3):294–303. Lin S, Munsie P, Hwang S

- A, Fitzgerald E, Cayo MR. 2002. Childhood asthma hospitalization and residential exposure to state route traffic. Environ Res 88(A):73–81. Link B, Phelan J. 1995. Social conditions as fundamental causes of disease. J Health Soc Behav (extra issue):80–94. Link B, Phelan J. 2000. Evaluating the fundamental cause explanation for social disparities in health. In: Handbook of Medical Sociology (Bird C, Conrad P, Freemont A, eds). Upper Saddle River, NJ:Prentice

- Hall. Lipfert FW. 2004. Air pollution and poverty: Does the sword cut both ways? J Environ Community Health 58:3–5. Luciano D, Lore R. 1975. Aggression and social experience in domesticated rats. J Comp Physiol Psych 88:917–923. Luginaah IN, Fung KY, Gorey KM, Webster G, Wills C. 2005. Association of ambient air pollution with respiratory hospi

� talization in a government

- designated “area of concern”: the case of Windsor, Ontario. Environ Health Perspect 113:290–296. Lupien SJ, King S, Meaney MJ, McEwen BS. 2000. Child’s stress hormone levels correlate with mother’s socio

� economic status and depressive state. Biol Psychiatry 48:976–980. Lupien SJ, King S, Meaney MJ, McEwen BS. 2001. Can poverty get under your skin? Basal cortisol levels and cognitive function in children from low and high socioeconomic status. Dev Psychopathol 13:653–676. Macleod J, Davey Smith G. 2003. Psychosocial factors and public health: a suitable case for treatment? J Epidemiol Community Health 57(8):565–570. Martins M, Fatigati F, Vespoli T, Martins L, Pereira L, Martins M,
et al. 2004. Influence of socioeconomic conditions on air pollution adverse health effects in elderly people: an analysis of six regions of São Paulo, Brazil. J Epidemiol Community Health 58:41–46. Mauderly JL, Samet J. 2009. Is there evidence for synergy among air pollutants in causing health effects? Environ Health Perspect 117:1–6. McConnell R, Berhane K, Gilliand F, London SJ, Islam T, Gauderman WJ, et al. 2002. Asthma in exercising children exposed to ozone: a cohort study. Lancet 359:386–391. McConnell R, Berhane K, Yao L, Jerrett M, Lurmann F, Gilliand FD, et al. 2006. Traffic, susceptibility, and child

� hood asthma. Environ Health Perspect 114:766–772. McEwen BS. 2006. Sleep deprivation as a neurobiologic and physiologic stressor: allostasis and allostatic load. Metabolism 55(10 suppl 2):S20–S23. McEwen BS. 2008. Understanding the potency of stressful early life experiences on brain and body function. Metabolism 57(supp 2):S11–S15. McEwen BS, Seeman TE. 1999. Protective and damaging effects of mediators of stress. Elaborating and testing the concepts of allostasis and allostatic load. Ann NY Acad Sci 896:30–47. Merritt M, Bennett G, Williams R, Sollers J, Thayer J. 2004. Low educational attainment, John Henryism, and cardiovas

� cular reactivity to and recovery from personally relevant stress. Psychosom Med 66(1):49–55. Messing K, Stellman JM. 2006. Sex, gender, and women’s occu

� pational health: the importance of considering mechanism. Environ Res 101:146–162. Miller G, Chen E. 2007. Unfavorable socioeconomic conditions in early life presage expression of proinflammatory pheno

� type in adolescence. Psychosom Med 69(5):402–409. Miller GE, Chen E, Sze E, Marin T, Arevalo JMG, Doll R, et al. 2008. A functional genomic fingerprint of chronic stress in humans: blunted glucocorticoid and increased NF

- kappaB signaling. Biol Psychiatry 64:266–272. Miller GE, Cohen S, Ritchey AK. 2002. Chronic psychological stress and the regulation of pro

- inflammatory cytokines: a glucocorticoid

- resistance model. Health Psychol 21:531–541. Moore K, Neugebauer R, Lurrmann F, Hall J, Brajer V, Alcorn S,
et al. 2008. Ambient ozone concentrations cause increased hospitalizations for asthma in children: an 18

- year study in Southern California. Environ Health Perspect 116:1063–1070. Morello

- Frosch R, Shenassa ED. 2006. The environmental “risk

� scape” and social inequality: implications for explaining maternal and child disparities. Environ Health Perspect 114:1150–1153. Muntner S, ed. 1963. The Medical Writings of Moses Maimonides: Teatise on Asthma. Philadelphia, PA:Lippincott. National Environmental Justice Advisory Council. 2004. Ensuring Risk Reduction in Communities with Multiple Stressors: Environmental Justice and Cumulative Risks/ Impacts. New Orleans, LA:Cumulative Risks/Impacts Work Group, National Environmental Justice Advisory Council. Nel A. 2001. The role of particulate pollutants in pulmonary inflammation and asthma: evidence for the involvement of organic chemicals and oxidative stress. Curr Opin Pulm Med 7:20–26. O’Neill M, Jerrett M, Kawachi I, Levy J, Cohen A, Gouveia N,
et al. 2003. Health, wealth, and air pollution: advancing the

� ory and method. Environ Health Perspect 111:1861–1870. O’Neill M, McMichael A, Schwartz J, Wartenberg D. 2007 a

. Poverty, environment, and health: the role of environ

� mental epidemiology and environmental epidemiologists. Epidemiology 18(6):664–668. O’Neill MS, Veves A, Sarnat JA, Zanobetti A, Gold DR, Economides PA, et al. 2007 b . Air pollution and inflamma

� tion in type 2 diabetes: a mechanism for susceptibility. Occup Environ Med 64(3):373–379.Clougherty and Kubzansky



### 1358 volume 117 | number 9 | September 2009 • Environmental Health Perspectives Ockenfels MC, Porter L, Smyth J, Kirschbaum C, Hellhammer DH. 1995. Effect of chronic stress associated with unemploy

� ment on salivary cortisol levels, diurnal rhythm, and acute stress reactivity. Psychosom Med 57:460–467. Oftedal B, Brunekreef B, Nystad W, Madsen C, Walker SE, Nafstad P. 2008. Residential outdoor air pollution and lung function in schoolchildren. Epidemiology 19(1):129–137. Oh Y

- M, Kim YS, Yoo SH, Kim SK, Kim DS. 2004. Association between stress and asthma symptoms: a population

- based study. Respirology 9:363–368. Pappas G, Queen S, Hadden W, Fisher G. 1993. The increasing disparity and mortality between socioeconomic groups in the United States, 1960 and 1986. N Eng J Med 329:103–109. Pekkanen J, Timonen K, Ruuskanen J, Reponen A, Mirmes A. 1997. Effects of ultrafine and fine particles in urban air on peak expiratory flow among children with asthmatic symp

� toms. Environ Res 74:24–33. Peters A. 2005. Particulate matter and heart disease: evidence from epidemiological studies. Toxicol Appl Pharmacol 207(2):477–482. Peters JL, Kubzansky LD, McNeely E, Schwartz J, Spiro A, Sparrow D, et al. 2007. Stress as a potential modifier of the impact of lead levels on blood pressure: The Normative Aging Study. Environ Health Perspect 115:1154–1159. Piro F, Madsen C, Naess O, Nafstad P, Claussen B. 2008. A comparison of self reported air pollution problems and GIS

- modeled levels of air pollution in people with and without chronic diseases. Environ Health 7:9; doi: 10.1186/ 1476

- 069X

- 7

- 9 [Online 28 February 2008]. Pope C III. 2002. Lung cancer, cardiopulmonary mortality, and long

- term exposure to fine particulate air pollution. JAMA 287:1132–1141. Pope C III, Thun M, Namboordiri M, Dockery D, Evans J, Speizer F. 1995. Particulate air pollution as a predictor of mortality in a prospective study of U.S. adults. Am J Respir Crit Care Med 151(3):669–674. Putz V, Johnson BL, Setzer JV. 1977. Effects of CO on Vigilance Performance. NIOSH Publication 77

- 124. Washington, DC:Government Printing Office. Rahman I, MacNee W. 2000. Oxidative stress and regulation of glutathione in lung inflammation. Eur Respir J 16:534–554. Rojas

- Martinez R, Perez

- Padilla R, Olaiz

- Fernandez G, Mendoza

- Alvarado L, Moreno

- Macias H, Fortoul T, et al. 2007. Lung function growth in children with long

- term exposure to air pollutants in Mexico City. Am J Respir Crit Care Med 176:377–384. Ronsaville DS, Municchi G, Laney C, Cizza G, Meyer SE, Haim A,
et al. 2006. Maternal and environmental factors influence the hypothalmic

- pituitary

- adrenal axis response to corticotropin

releasing hormone infusion in offspring of mothers with or without mood disorders. Dev Psychopathol 18:173–194. Rosenlund M, Forastiere F, Porta D, De Sario M, Badaloni C, Perucci CA. 2008. Traffic

- related air pollution in relation to respiratory symptoms, allergic sensitization, and lung func

� tion in school children. Thorax; doi:10.1136/thx.2007.094953 [Online 13 October 2008]. Rossi

- George A, Virgolini MB, Weston DD, Cory

- Slechta DA. 2009. Alterations in glucocorticoid negative feedback following maternal Pb, prenatal stress, and the combination: a poten

� tial biological unifying mechanism for their corresponding disease profiles. Toxicol Appl Pharmacol 234(1):117–127. Rotton J, Frey J, Barry T. 1979. The air pollution experience and physical aggression. J Appl Soc Psychol 9:397–412. Rückerl R, Ibald

- Mulli A, Koenig W, Schneider A, Woelke G, Cyrys J, et al. 2006. Air pollution and markers of inflam

� mation and coagulation in patients with coronary heart disease. Am J Respir Crit Care Med 173(4):432–441. Ryan P, LeMasters G, Biswas P, Levin L, Hu S, Lindsey M, et al. 2007. A comparison of proximity and land use regression traffic exposure models and wheezing in infants. Environ Health Perspect 115:278–284. Sandberg S, Jarvenpaa S, Pettinen A, Paton J, McCann D. 2004. Asthma exacerbations in children immediately fol

� lowing stressful life events: a Cox’s hierarchical regres

� sion. Thorax 59:1046–1051. Sandberg S, Paton J, Ahola S, McCann D, McGuinness D, Hillary CR, et al. 2000. The role of acute and chronic stress in asthma attacks in children. Lancet 356(9234): 982–987

. Schauer JJ, Lough GC, Schafer MM, Christensen WF, Arndt MF, DeMinter JT, et al. 2006. Characterization of metals emitted from motor vehicles. Res Rep Health Eff Inst 133:1–7. Schikowski T, Sugiri D, Ranft U, Gehring U, Heinrich J, Wichmann E, et al. 2005. Long

- term air pollution exposure and living close to busy roads are associated with COPD in women. Resp ir Res 6(1) :152. Seeman TE, Crimmins EM, Huang M

- H, Singer B, Bucur A, Gruenewald TL, et al. 2004. Cumulative biological risk and socio

- economic differences in mortality: MacArthur Studies of Successful Aging. Soc Sci Med 58:1985–1997. Seeman TE, Singer B. 2002. Psychosocial factors and the devel

� opment of allostatic load. Psychosom Med 64:395–406. Seeman TE, Singer B, Rowe JW, Horwitz RI, McEwen BS. 1997. Price of adaptation: allostatic load and its health conse

� quences. Arch Int ern Med 157:2259–2268. Seeman TE, Singer BH, Ryff CD, Dienberg Love G, Levy

Storms L. 2002. Social relationships, gender, and allostatic load across two age cohorts. Psychosom Med 64:395–406. Segerstrom S, Miller G. 2004. Psychological stress and the human immune system: a meta

- analytic study of 30 years of inquiry. Psychol Bulletin 130(4):601–630. Selye H. 1936. A syndrome produced by diverse nocuous agents. Nature 138 :32

. Shonkoff JP, Phillips DA. 2000. From Neurons to Neighborhoods: The Science of Early Childhood Development, Washington, DC: National Academy Press. Singh GK, Hiatt RA. 2006. Trends and disparities in socio

� economic and behavioral characteristics, life expectancy, and cause

- specific mortality of native

- born and foreign

born populations in the United States, 1979–2003. Int J Epidemiol 35(4):903–919. Sinton CM, Fitch TE, Petty F, Haley RW. 2000. Stressful manipu

� lations that elevate corticosterone reduce blood

- brain barrier permeability to pyridostigmine in the rat. Toxicol Appl Pharmacol 165:99–105. Sirivelu MP, MohanKumar SMJ, Wagner JG, Harkema JR, MohanKumar PS. 2006. Activation of the stress axis and neurochemical alterations in specific brain areas by con

� centrated ambient particle exposure with concomitant aller

� gic airway disease. Environ Health Perspect 114:870–874. Sternberg E, Choursos G, Wilder R, Gold P. 1992. The stress response and the regulation of inflammatory disease. Ann Intern Med 117:854–866. Strahilevitz M, Strahilevitz A, Miller J. 1979. Air pollution and the admission rate of psychiatric patients. Am J Psychiatry 136:205–207. Subramanian SV, Chen J, Rehropf DH, Waterman PD, Krieger N. 2005. Racial disparities in context: a multilevel analysis of neighborhood variations in poverty and excess mortality among black populations in Massachusetts. Am J Pub lic H ealth 95(2):260–265. Sundaram V, Helweg

- Larsen K, Laursen B, Bjerregaard P. 2004. Physical violence, self rated health, and morbidity: is gen

� der signficant for victimisation? J Epidemiol Community Health 58:65–70. Taylor SE, Klein LC, Lewis BP, Gruenewald TL, Gurung RAR, Updegraff JA. 2000. Biobehavioral responses to stress in females; tend

- and

- befriend, not fight

- or

- flight. Psychol Rev 107(3):411–429. Thompson VLS. 1996. Perceived experiences of racism as stressful life events. Comm unity Men Health J 32:223–233. Umetsu DT, McIntire JJ, Akbari O, Macaubas C, DeKruyff RH. 2002. Asthma: an epidemic of dysregulated immunity. Nat Immunol 3(8):715–720. U.S. Environmental Protection Agency. 2008. Integrated Science Assessment for Oxides of Nitrogen—Health Criteria. Research Triangle Park, NC:National Center for Environmental Assessment, Office of Research and Development. Viltart O, Vanbesien

- Maillot CC. 2007. Impact of prenatal stress on neuroendocrine programming. ScientificWorldJournal 7:1493–1537. Vineis P, Hoek G, Krzyzanowski M, Vigna

- Taglianti F, Veglia F, Airoldi L, et al. 2007. Lung cancers attributable to environ

� mental tobacco smoke and air pollution in non

- smokers in different European countries: a prospective study. Environ Health 6:7; doi:10.1186/1476

- 069X

- 6

- 7 [Online 15 February 2007]. Virgolini MB, Bauter MR, Weston DD, Cory

- Slechta DA. 2006. Permanent alterations in stress responsivity in female offspring subjected to combined maternal lead exposure and/or stress. Neurotoxicology 27(1):11–21. Virgolini MB, Chen K, Weston DD, Bauter MR, Cory

- Slechta DA. 2005. Interactions of chronic lead exposure and inter

� mittent stress: consequences for brain catecholamine systems and associated behaviors and HPA axis function. Toxicol Sci 87(2):469–482. Weiss B, Bellinger DC. 2006. Social ecology of children’s vul

� nerability to environmental pollutants. Environ Health Perspect 114:1479–1485. Wheeler B, Ben

- Shlomo Y. 2005. Environmental equity, air quality, socioeconomic status, and respiratory health: a linkage analysis of routine data from the Health Survey for England. J Epidemiol Community Health 59:948–954. Wright RJ, Cohen S, Carey V, Weiss ST, Gold DR. 2002. Parental stress as a predictor of wheezing in infancy: a prospective birth

- cohort study. Am J Respir Crit Care Med 165:358–365. Wright RJ, Finn P, Contreras JP, Cohen S, Wright RO, Staudenmayer J, et al. 2004. Chronic caregiver stress and IgE expression, allergen

- induced proliferation, and cytokine profiles in a birth cohort predisposed to atopy. J Allergy Clin Immunol 113:1051–1057. Zanobetti A, Schwartz J. 2000. Race, gender, and social status as modifiers of the effects of PM 10 on mortality. J Occup Environ Med 42:469–474. Zhu Y, Hinds WC, Kim S, Sioutas C. 2002. Concentration and size distribution of ultrafine particles near a major high

� way. J Air Waste Manag Assoc 52:1032–1041.