Grantee Research Project Results
Final Report: Hypertension in Mexican-Americans: Assessing Disparities in Air Pollutant Risks
EPA Grant Number: R834581Title: Hypertension in Mexican-Americans: Assessing Disparities in Air Pollutant Risks
Investigators: Symanski, Elaine , Bondy, Melissa L. , Chen, Lin-An , Jimenez, Maria , Strom, Sara , Chan, Wenyaw
Institution: The University of Texas School of Public Health , The University of Texas MD Anderson Cancer Center , National Chiao-Tung University
Current Institution: The University of Texas School of Public Health , National Chiao-Tung University , The University of Texas MD Anderson Cancer Center
EPA Project Officer: Hahn, Intaek
Project Period: August 1, 2010 through July 31, 2014 (Extended to July 31, 2016)
Project Amount: $1,250,000
RFA: Understanding the Role of Nonchemical Stressors and Developing Analytic Methods for Cumulative Risk Assessments (2009) RFA Text | Recipients Lists
Research Category: Human Health
Objective:
Based on data from the U.S. Census Bureau, the Hispanic population is the fastest growing minority in the Nation. In 2010, there were approximately 50.5 million Hispanics in the United States. Among Hispanics, hypertension is on the rise and is highest among the population of Mexican origin. This is especially important when one considers that morbidity and mortality associated with hypertension is greater among this population compared with other ethnic/racial groups. Cardiovascular disease (CVD), which is associated with high blood pressure, remains the leading cause of death among U.S. Hispanics.
Studies have shown an association between air pollutants (especially fine particulate matter) and hypertension via oxidative stress and inflammatory pathways. Yet less is known about the effects of specific sources or constituents of particulate matter, such as diesel particulate matter or polycyclic aromatic hydrocarbons (PAHs). Further, the impact of psychosocial stressors, as well as the combined effects of air pollution and psychosocial stressors, on hypertension is not clear. Acculturative stress also may be a risk factor, and studies indicate that high-acculturated individuals are more likely to have hypertension than those who were less acculturated.
In this project, we addressed the gap in the literature by conducting two epidemiologic investigations: (1) a cross-sectional analysis of PAHs and diesel particulate matter exposures and hypertension (not originally proposed) (Bangia, et al., 2015) and (2) a case-control study of ozone and fine particulate matter, psychosocial stressors and hypertension (Rammah, et al., in preparation for submission). Both studies drew on participants from the ongoing Mano a Mano cohort study of individuals of Mexican origin living in Houston, Texas, which was established in 2001 in the Department of Epidemiology at the University of Texas MD Anderson Cancer Center. In personal interviews administered at baseline, participants provide information about sociodemographic and other characteristics. All participants receive a follow-up phone survey every 6 months. In our initial investigation, we relied on secondary data. In our second investigation, we engaged the community in the research process (Symanski, et al., 2015) and collected primary data.
In this project, we also developed new statistical methods, using the method similar to the ANOVA approach for a continuous outcome that allowed for a rigorous evaluation of interaction between chemical and nonchemical stressors in a logistic regression framework. Results from the developed method are easier to interpret as compared to results from a multiple logistic regression model with a product term. In addition to the proposed method, we also developed a novel concept of approaching interaction by borrowing the concept of "isobole" in toxicology to define interaction in terms of a "statistical isobole." This approach allows for a test of interaction between two covariates beyond the form of product term. The asymptotic properties of the proposed statistical isobole also were derived and mathematically proved.
Summary/Accomplishments (Outputs/Outcomes):
A Cross-Sectional Analysis of PAHs and Diesel Particulate Matter (DPM) Exposures and Hypertension Among Individuals of Mexican Origin.
Modeled estimates of ambient air levels of PAHs and DPM were extracted from the 2002 and 2005 National-Scale Air Toxics Assessment (NATA) developed by the U.S. Environmental Protection Agency (EPA). To generate the nationwide estimates of ambient air levels of toxic air pollutants (reported in units of µg/m3), depending on the source of emissions, NATA uses the National Emissions Inventory or the National Mobile Inventory Model to input data into two models, the Assessment System for Population Exposure Nationwide and the Human Exposure Model 3, respectively. Using geographical information systems, we linked modeled annual estimates of PAHs and diesel particulate matter at the census tract level to baseline residential addresses of 11,218 Mano a Mano cohort members who enrolled from 2001 to 2003 (2002 NATA) or 2004 to 2006 (2005 NATA estimates).
For each enrollment period, we applied mixed-effects logistic regression models to determine associations between diesel particulate matter and PAHs, separately, and self-reported hypertension while adjusting for confounders and the clustering of observations within census tracts and households. Following adjustment for age, there was a dose-dependent, positive association between PAHs and hypertension (medium exposure, adjusted odds ratio (OR) = 1.09, 95 percent CI: 0.88–1.36; high exposure, OR=1.40, 95 percent CI: 1.01–1.94) for individuals enrolled during 2001–2003. Associations were generally similar in magnitude but less precise, following adjustment for age, gender, smoking and body mass index. We did not detect an association for the later period. There was no evidence of an association between residential levels of diesel particulate matter and hypertension. There were little to modest differences in the associations based on how long participants lived at their current addresses at baseline (< 5 years as compared to > 5 years).
Investigating Independent and Interacting Effects of Air Pollution and Psychosocial Stressors on Hypertension among Individuals of Mexican Origin
Using a Community-Engaged Approach To Develop a Bilingual Survey About Psychosocial Stressors
In our project, we established a Neighborhood Council of Advisors (NCA) to provide input on our activities. The 16-member NCA reflected the complexity of the neighborhoods under study and included a janitor, a nurse, a county employee, a housewife, a retiree, a student, an accountant, a legal case worker, a community organizer, a community center director, a school bus driver, a lay religious leader and four people unable to work because of disabilities. We conducted focus group discussions among women (n = 2) and men (n = 2) separately in the language preferred by participants. Following analysis of the focus group discussions and with feedback from the NCA, themes emerged that guided the development of a questionnaire (36 questions). We then pilot tested a bilingual survey about psychosocial stressors among a subset of Mano a Mano cohort members. Possible responses to each question in the survey included: "No, not at all," "Yes, a little bit," "Yes, sometimes," "Yes, a lot of the time" and "Yes, most of the time." We administered the final 32-question survey, available in English and Spanish, to 2,481 Mano a Mano cohort members (selected based on their hypertension status) during regularly scheduled follow-up phone interviews. For the 21 psychosocial stressors, responses were later collapsed into three levels of low (no, not at all and yes, a little bit), medium (yes, sometimes) and high (yes, a lot of the time and yes, most of the time) categories of stress.
Air Pollution Exposure Assessment
To construct air pollution exposure estimates, we obtained validated hourly air pollution data for O3 and PM2.5 from January 2006 to December 2014 from the Texas Commission on Environmental Quality, the environmental agency for the state. We used data from all monitoring stations that continuously measured hourly O3 and PM2.5 concentrations in the Houston-Galveston-Brazoria region (i.e., Brazoria, Chambers, Fort Bend, Galveston, Harris, Liberty, Montgomery and Waller Counties). We excluded one O3 monitoring station and one PM2.5 monitoring station for having 25 percent or more missing observations over the study period. The number of O3 monitoring stations that were available each year ranged from 41 to 45: 41 in 2013; 42 in 2007, 2008, 2010 and 2014; 43 in 2006 and 2012; and 45 in 2009 and 2011. O3 monitoring stations were concentrated in Harris County (n = 35), with five monitoring stations in Galveston; four in Brazoria County; and one in each of the counties of Chambers, Fort Bend, Liberty and Montgomery. The number of PM2.5 stations included was 9 for 2006, 2011–2014, 10 for 2007–2008 and 11 for 2009–2010. There were 10 PM2.5 monitoring stations in Harris County, three monitoring stations in Galveston County and one in Montgomery County.
Exposure estimates were constructed using SAS (Version 9.4, SAS Institute, Cary, North Carolina) and ArcGIS (Release 10.2.2., Environmental Systems Research Institute, Redlands, California). We calculated the maximum average 8-hour O3concentration and the average 24-hour PM2.5 concentration for each monitoring station for each day from January 1, 2006, to December 31, 2014. Using the daily time series of O3 and PM2.5 concentrations, we computed an average for the 12-month period preceding baseline enrollment for every individual. Interpolation via inverse distance weighting (p = 2) was used to calculate exposure estimates for each individual, using the three closest monitoring stations to each participant's geocoded residential address. The range of outdoor residential levels of O3 was 27.5–42.1 ppb among cases and 23.8–44.0 ppb among controls. For PM2.5 , levels ranged from 9.5–14.9 mg/m3 for both cases and controls. Due to a lack of variability in estimated residential levels of PM2.5 (likely due to the limited number of monitors in the region), we excluded this pollutant from subsequent analyses.
Associations Between Air Pollution, Psychosocial Stressors and Hypertension
In univariate analyses, we observed a 50 percent increase in the odds of having hypertension among persons with a higher level of acculturation; there was more than a two-fold increase in the odds of having hypertension among persons born in the United States as compared to Mexico (and in individuals whose preferred language was English as compared to Spanish). In contrast to our acculturation metrics, we obtained equivocal results depending on the source of psychosocial stress. For example, we observed higher odds of prevalent hypertension with increasing stress level associated with caring for a sick family member or feeling stressed about one's own health. In contrast, we observed inverse associations for individuals experiencing any level of stress related to being separated from family or not having enough time for oneself. In both crude and adjusted models, our findings suggested that the odds of being hypertensive decrease with increasing ozone levels. There was little evidence that gender, BMI or psychosocial stress modified the ozone-hypertension association.
An ANOVA Type of Approach to Test of Interaction in Logistic Regression Frameworks
We developed an analytic approach for evaluating interactions between independent variables, which are discretized using a specific quantile breakdown. We completed an R program for implementing the proposed estimation and testing methods. We conducted a simulation study for examining the interaction effect based on this method. The results are close to our targeted error probability and the power for detecting the interaction effect between two covariates increases with the absolute value of the interaction effect. The simulation results also show that the proposed method is more powerful than the traditional logistic regression method in detecting the interaction effect. In addition, our method does not have an interpretation problem like what testing the product term in a logistic regression has. Recall that testing the significance of interaction through the product term in a logistic regression requires to fix the additive terms. Our method also can detect the interaction within any cell, with designated ranges for the chemical and non-chemical stressors. Our method also can be modified for testing higher way of interaction. We have also completed the application of these methods with a subset of the data that were collected. In this application, we evaluated ozone and four social stressors.
A manuscript describing this work is being prepared. We are now in process of writing the manuscript for submission.
On Interaction Through a Statistical Isobole
We introduced and mathematically developed a novel concept of a statistical isobole to assess interaction. Using the proposed statistical isobole, we classified a sample point as synergistic, antagonistic or no-interaction effect. We further introduced an interaction assessment index based on this statistical isobole and used this index to conduct statistical inferences on all sample points in the isobole about their interaction properties (synergistic, antagonistic or no-interaction effect). The mathematical properties of the interaction assessment index and its related statistical tests were derived. Particularly, the asymptotic properties of these tests were presented and proved and we demonstrated that they were easily applicable using a normal-distribution procedure. The proposed method is more robust than traditional methods. It also allows for making inferences on interaction beyond the form of a product term. As our outcome variable was dichotomous in nature (i.e., self-reported hypertension), we applied the proposed method to a dataset in NHANES III for studying the interaction effect of body mass index and total serum cholesterol on systolic blood pressure.
Conclusions:
Our study was built on a limited number of prior investigations of the association between ambient pollution and hypertension by focusing on a relatively young cohort of predominantly adult women of Mexican origin. In our cross-sectional evaluation of the associations between hypertension and residential air levels of DPM and PAHs among individuals of Mexican origin, our results indicate an association between PAHs and hypertension for individuals enrolled in the 2001–2003 time period but not in the later time period. No associations were detected for DPM in either period.
We used a mixed methods approach in our second epidemiologic investigation of the independent and interacting effects of air pollution and psychosocial stress. Unexpectedly, we found little variability in residential air levels of PM2.5 among our population, which is likely due to the limited number of air monitoring stations measuring exposure to PM2.5 in the study area. Future analyses will evaluate associations between fine particulate matter and hypertension using other (modeled) sources or data. We did not confirm earlier studies that showed a positive association between O3 and hypertension. However, our results are consistent with some studies on short-term exposure that reported inverse associations between ozone and measured blood pressure or hypertension. There was little effect measure modification due to exposure to psychosocial stressors, although the direction of association changed for individuals who reported high levels of stress associated with having unknown people in their neighborhood. Future research is needed to evaluate the impact of both short- and long-term ozone exposures on incident hypertension, further examine associations with specific chemical constituents of particulate matter and the modifying role of psychosocial stressors.
In methodology development, our approach using an ANOVA type of analysis in detecting interaction effect is more powerful than the method through testing the significance of a product term in a traditional logistic regression model,. This method can be applied when covariates are continuous by discretization. In addition, our method can be modified for testing higher way interaction effects. Our isobole approach may potentially advance our capabilities to test for interaction under a new framework. The proposed method can detect interaction beyond its traditional form that is often represented by a product term between two covariates.
Journal Articles on this Report : 3 Displayed | Download in RIS Format
Other project views: | All 5 publications | 3 publications in selected types | All 3 journal articles |
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Type | Citation | ||
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Bangia KS, Symanski E, Strom SS, Bondy M. A cross-sectional analysis of polycyclic aromatic hydrocarbons and diesel particulate matter exposures and hypertension among individuals of Mexican origin. Environmental Health 2015;14:51. |
R834581 (2015) R834581 (Final) |
Exit Exit Exit |
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Payne-Sturges DC, Korfmacher KS, Cory-Slechta DA, Jimenez M, Symanski E, Carr Shmool JL, Dotson-Newman O, Cloughtery JE, French R, Levy JI, Laumbach R, Rodgers K, Bongiovanni R, Scammell MK. Engaging communities in research on cumulative risk and social stress-environment interactions: lessons learned from EPA's STAR Program. Environmental Justice 2015;8(6):203-212. |
R834581 (Final) R834576 (Final) R834577 (Final) R834578 (Final) R834579 (Final) R834580 (Final) R834582 (Final) |
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Symanski E, Karpman M, Jimenez M, Lopez DS, Felknor SA, Upadhyaya M, Strom SS, Bondy ML. Using a community-engaged approach to develop a bilingual survey about psychosocial stressors among individuals of Mexican origin. Journal of Health Care for the Poor and Underserved 2015;26(4):1456-1471. |
R834581 (2014) R834581 (2015) R834581 (Final) |
Exit Exit |
Supplemental Keywords:
Air pollution, epidemiology, exposure, sensitive populations, hypertension, cumulative exposure, cumulative risk, hypertension, air pollution, latino community, hispanics, cardiovascular disease, human health risk, Health, Scientific Discipline, ENVIRONMENTAL MANAGEMENT, Risk Management, Health Risk Assessment, Risk Assessments, Biochemistry, Biology, cumulative exposure, cumulative risk, hypertension, air pollution, latino community, sensitive subjects, hispanics, cardiovascular disease, human health riskProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.
Project Research Results
- 2015 Progress Report
- 2014 Progress Report
- 2013 Progress Report
- 2012 Progress Report
- 2011 Progress Report
- Original Abstract
3 journal articles for this project