Academic journal article Environmental Health Perspectives

Long-Term Exposure to Ambient Ozone and Progression of Subclinical Arterial Disease: The Multi-Ethnic Study of Atherosclerosis and Air Pollution

Academic journal article Environmental Health Perspectives

Long-Term Exposure to Ambient Ozone and Progression of Subclinical Arterial Disease: The Multi-Ethnic Study of Atherosclerosis and Air Pollution

Article excerpt


Ground-level ozone ([O.sub.3]) is a powerful oxidizing agent and is one of the most harmful air pollutants currently addressed by air quality standards in the European Union and United States. Over recent decades, [O.sub.3] has not shown a discernible trend of decline in Europe and the United States, and it will likely remain an important environmental health issue, especially given projected increases in temperature related to climate change (EEA 2015), since ground-level ozone is formed when a complex set of chemical reactions is triggered by heat and sunlight (U.S. EPA 2013). Strong and consistent evidence for health effects of [O.sub.3] exposure has been demonstrated for the short-term exposure effects on the respiratory system (EEA 2011; U.S. EPA 2013). The literature on cardiovascular effects of long-term exposure to [O.sub.3] have been considered less consistent (U.S. EPA 2013; Jerrett et al. 2009) and focused primarily on mortality effects. (Carey et al. 2013; Di et al. 2017; Jerrett et al. 2009; Turner et al. 2016; Zanobetti and Schwartz 2011). There has been little attempt to investigate the underlying association between long-term exposure to [O.sub.3] and subclinical vascular disease (Breton et al. 2012).

Intima-media thickness of common carotid artery ([IMT.sub.CCA]) and coronary artery calcification (CAC) are noninvasive markers of subclinical arterial disease that predict risk of coronary heart disease and stroke in people without cardiovascular diseases (CVDs) (Stein et al. 2008). Compared to [IMT.sub.CCA], carotid plaque (CP) represents a later stage of arterial injury where diffuse thickening of the intima media complex accelerates focally, leading to atherosclerotic plaque formation (Stein et al. 2008). CP presence and burden are associated with increased risk of CVD events, and this measure improves the predictive accuracy of [IMT.sub.CCA] (Gepner et al. 2015).

To date, the association of long-term exposure to [O.sub.3] and [IMT.sub.CCA] has only been reported in a cross-sectional study of schoolchildren (Breton et al. 2012). Findings on the effects of [O.sub.3] exposure on progression of [IMT.sub.CCA], CAC, and CP have not been reported previously.

The Multi-Ethnic Study of Atherosclerosis (MESA, https:// is a population-based prospective cohort study of adults free of CVD at baseline with repeated measurements of [IMT.sub.CCA], CAC, and CP for up to 10 y. This provides a unique opportunity to assess the longitudinal relationship between long-term exposure to [O.sub.3] and progression of [IMT.sub.CCA], CAC, and CP in a well-characterized cohort of adults.


Study Population

Study objectives and design have been previously published (Kaufman et al. 2012). MESA enrolled 6,814 participants aged 45-84 y without a clinical history of CVD in six U.S. city regions (Baltimore, Maryland; Chicago, Illinois; Los Angeles County, California; New York City, New York; St. Paul, Minnesota; and Winston-Salem, North Carolina). Recruitment of the MESA study started in 2000, and participants were followed for approximately 10 y. Participants had to meet age and race/ethnicity eligibility criteria and be free of prevalent CVD to optimize the study of subclinical CVD progression and its association with predictors of clinical CVDs. Between 2005 and 2007, the MESA Air Pollution Study (MESA Air) recruited an additional 257 participants from the Los Angeles Basin and the New York region to capitalize on exposure heterogeneity in the vicinity of two existing MESA population communities and to increase the size of the cohort for follow-up of clinical events. CP, [IMT.sub.CCA], and CAC, together with standard cardiovascular risk factors, sociodemographic factors, lifestyle habits, and psychosocial factors, were collected for individuals at baseline and in the follow-up examinations (Table 1; Table S1). Participants had an average of two measurements (minimum to maximum: one to three times) for [IMT. …

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