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Jane E. Clougherty,¹ Jonathan I. Levy,¹ Laura D. Kubzansky,² P. Barry Ryan,³ Shakira Franco Suglia,^1,4 Marina Jacobson Canner,⁵ and Rosalind J. Wright^2,5

¹Department of Environmental Health, and ²Department of Society, Human Development, and Health, Harvard School of Public Health, Boston, Massachusetts, USA; ³Department of Environmental Health, Rollins School of Public Health, Emory University, Atlanta, Georgia, USA; ⁴Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, USA; ⁵Channing Laboratory, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, USA

Abstract
Background: Disproportionate life stress and consequent physiologic alteration (i.e., immune dysregulation) has been proposed as a major pathway linking socioeconomic position, environmental exposures, and health disparities. Asthma, for example, disproportionately affects lower-income urban communities, where air pollution and social stressors may be elevated.

Objectives: We aimed to examine the role of exposure to violence (ETV) , as a chronic stressor, in altering susceptibility to traffic-related air pollution in asthma etiology.

Methods: We developed geographic information systems (GIS) –based models to retrospectively estimate residential exposures to traffic-related pollution for 413 children in a community-based pregnancy cohort, recruited in East Boston, Massachusetts, between 1987 and 1993, using monthly nitrogen dioxide measurements for 13 sites over 18 years. We merged pollution estimates with questionnaire data on lifetime ETV and examined the effects of both on childhood asthma etiology.

Results: Correcting for potential confounders, we found an elevated risk of asthma with a 1-SD (4.3 ppb) increase in NO₂ exposure solely among children with above-median ETV [odds ratio (OR) = 1.63 ; 95% confidence interval (CI) , 1.14–2.33) ]. Among children always living in the same community, with lesser exposure measurement error, this association was magnified (OR = 2.40 ; 95% CI, 1.48–3.88) . Of multiple exposure periods, year-of-diagnosis NO₂ was most predictive of asthma outcomes.

Conclusions: We found an association between traffic-related air pollution and asthma solely among urban children exposed to violence. Future studies should consider socially patterned susceptibility, common spatial distributions of social and physical environmental factors, and potential synergies among these. Prospective assessment of physical and social exposures may help determine causal pathways and critical exposure periods.

Key words: childhood asthma, exposure to violence (ETV) , geographic information systems (GIS) , intraurban variability, nitrogen dioxide (NO₂) , social–environmental synergy, stress. Environ Health Perspect 115:1140–1146 (2007) . doi:10.1289/ehp.9863 available via http://dx.doi.org/ [Online 22 March 2007]

Address correspondence to J.E. Clougherty, Harvard School of Public Health ; Department of Environmental Health, Landmark Center Room 404, P.O. Box 15677, Boston, MA 02215 USA. Telephone: (617) 384-8811. Fax: (617) 384-8859. E-mail: jcloughe@hsph.harvard.edu

Analysis was supported by American Lung Association Lung Health Dissertation grant (J.E.C.) . Data collection and analysis for the nitrogen dioxide passive network and violence exposure assessment were supported by the Massachusetts Port Authority (P.B.R.) and K08 HL 04187 (R.J.W.) , respectively. J.I.L. was supported by Health Effects Institute grant 4727-RFA04-5/05-1 and National Institutes of Health grant R03 ES013988. S.F.S. was supported by National Research Service Award F31 HD049317 and T32ES007142.

The authors declare they have no competing financial interests.

Received 27 October 2006 ; accepted 22 March 2007.