Nuoo-Ting Molitor

Assessing Uncertainty in Spatial Exposure Models for Air Pollution Health Effects Assessment

Background Although numerous epidemiologic studies now use models of intraurban exposure, there has been little systematic evaluation of the performance of different models. Objectives In this present article we proposed a modeling framework for assessing exposure model performance and the role of spatial autocorrelation in the estimation of health effects. Methods We obtained data from an exposure measurement substudy of subjects from the Southern California Children’s Health Study. We examined how the addition of spatial correlations to a previously described unified exposure and health outcome modeling framework affects estimates of exposure–response relationships using the substudy data. The methods proposed build upon the previous work, which developed measurement–error techniques to estimate long-term nitrogen dioxide exposure and its effect on lung function in children. In this present article, we further develop these methods by introducing between- and within-community spatial autocorrelation error terms to evaluate effects of air pollution on forced vital capacity. The analytical methods developed are set in a Bayesian framework where multistage models are fitted jointly, properly incorporating parameter estimation uncertainty at all levels of the modeling process. Results Results suggest that the inclusion of residual spatial error terms improves the prediction of adverse health effects. These findings also demonstrate how residual spatial error may be used as a diagnostic for comparing exposure model performance.

Identifying vulnerable populations through an examination of the association between multipollutant profiles and poverty

Recently, concerns have centered on how to expand knowledge on the limited science related to the cumulative impact of multiple air pollution exposures and the potential vulnerability of poor communities to their toxic effects. The highly intercorrelated nature of exposures makes application of standard regression-based methods to these questions problematic due to well-known issues related to multicollinearity. Our paper addresses these problems by using, as its basic unit of inference, a profile consisting of a pattern of exposure values. These profiles are grouped into clusters and associated with a deprivation outcome. Specifically, we examine how profiles of NO(2)-, PM(2.5)-, and diesel- (road and off-road) based exposures are associated with the number of individuals living under poverty in census tracts (CTs) in Los Angeles County. Results indicate that higher levels of pollutants are generally associated with higher poverty counts, though the association is complex and nonlinear. Our approach is set in the Bayesian framework, and as such the entire model can be fit as a unit using modern Bayesian multilevel modeling techniques via the freely available WinBUGS software package, (1) though we have used custom-written C++ code (validated with WinBUGS) to improve computational speed. The modeling approach proposed thus goes beyond single-pollutant models in that it allows us to determine the association between entire multipollutant profiles of exposures with poverty levels in small geographic areas in Los Angeles County.

Do Stress Trajectories Predict Mortality in Older Men? Longitudinal Findings from the VA Normative Aging Study

We examined long-term patterns of stressful life events (SLE) and their impact on mortality contrasting two theoretical models: allostatic load (linear relationship) and hormesis (inverted U relationship) in 1443 NAS men (aged 41–87 in 1985; M = 60.30, SD = 7.3) with at least two reports of SLEs over 18 years (total observations = 7,634). Using a zero-inflated Poisson growth mixture model, we identified four patterns of SLE trajectories, three showing linear decreases over time with low, medium, and high intercepts, respectively, and one an inverted U, peaking at age 70. Repeating the analysis omitting two health-related SLEs yielded only the first three linear patterns. Compared to the low-stress group, both the moderate and the high-stress groups showed excess mortality, controlling for demographics and health behavior habits, HRs = 1.42 and 1.37, ps <.01 and <.05. The relationship between stress trajectories and mortality was complex and not easily explained by either theoretical model.

A Bayesian approach to functional-based multilevel modeling of longitudinal data: applications to environmental epidemiology

Flexible multilevel models are proposed to allow for cluster-specific smooth estimation of growth curves in a mixed-effects modeling format that includes subject-specific random effects on the growth parameters. Attention is then focused on models that examine between-cluster comparisons of the effects of an ecologic covariate of interest (e.g. air pollution) on nonlinear functionals of growth curves (e.g. maximum rate of growth). A Gibbs sampling approach is used to get posterior mean estimates of nonlinear functionals along with their uncertainty estimates. A second-stage ecologic random-effects model is used to examine the association between a covariate of interest (e.g. air pollution) and the nonlinear functionals. A unified estimation procedure is presented along with its computational and theoretical details. The models are motivated by, and illustrated with, lung function and air pollution data from the Southern California Childrens Health Study.

Blood Pressure Differences Associated With Optimal Macronutrient Intake Trial for Heart Health (OMNIHEART)–Like Diet Compared With a Typical American DietNovelty and Significance

The Dietary Approaches to Stop Hypertension-Sodium (DASH-Sodium) trial demonstrated beneficial effects on blood pressure (BP) of the DASH diet with lower sodium intake when compared with typical American diet. The subsequent Optimal Macronutrient Intake Trial for Heart Health (OMNIHEART) trial reported additional BP benefits from replacing carbohydrate in the DASH diet with either protein or monounsaturated fats. The primary aim of this study is to assess possible BP benefits of an OMNIHEART-like diet in free-living Americans using cross-sectional US population data of the International Study of Macronutrients, Micronutrients and Blood Pressure (INTERMAP) study. The INTERMAP data include four 24-hour dietary recalls, 2 timed 24-hour urine collections, 8 BP readings for 2195 individuals aged 40 to 59 years from 8 US INTERMAP population samples. Analyses are conducted using 2 approaches: (1) regression of BP on a linear OMNIHEART nutrient score calculated for each individual and (2) a Bayesian approach comparing estimated BP levels of an OMNIHEART-like nutrient profile with a typical American nutrient profile. After adjustment for potential confounders, an OMNIHEART score higher by 1 point was associated with systolic/diastolic BP differences of −1.0/−0.5 mm Hg (both P<0.001). Mean systolic/diastolic BPs were 111.3/68.4 and 115.2/70.6 mm Hg for Bayesian OMNIHEART and Control profiles, respectively, after controlling for possible confounders, with BP differences of −3.9/−2.2 mm Hg, P(difference ⩽0)=0.98/0.96. Findings were comparable for men and women, for nonhypertensive participants, and with adjustment for antihypertensive treatment. Our findings from data on US population samples indicate broad generalizability of OMNIHEART results beyond the trial setting and support recommendations for an OMNIHEART-style diet for prevention/control of population-wide adverse BP levels.The DASH-Sodium trial demonstrated beneficial effects on blood pressure (BP) of the DASH diet with lower sodium intake compared to typical American diet. The subsequent OMNIHEART trial reported additional BP benefits from replacing carbohydrate in the DASH diet with either protein or monounsaturated fats. The primary aim of this study is to assess possible BP benefits of an OMNIHEART-like diet in free-living Americans using cross-sectional U.S. population data of the INTERMAP Study. INTERMAP data include four 24-h dietary recalls, two timed 24-h urine collections, eight BP readings for 2,195 individuals ages 40-59 from eight US INTERMAP population samples. Analyses are conducted using two approaches: 1. Regression of BP on a linear OMNIHEART nutrient score calculated for each individual, and 2. A Bayesian approach comparing estimated BP levels of an OMNIHEART-like nutrient profile with a typical American nutrient profile. After adjustment for potential confounders, an OMNIHEART score higher by one point was associated with systolic/diastolic BP differences of −1.0/−0.5 mmHg (both P<0.001). Mean systolic/diastolic BPs were 111.3/68.4 and 115.2/70.6 mmHg for Bayesian OMNIHEART and Control profiles respectively, after controlling for possible confounders, with BP differences of −3.9/−2.2 mmHg, Pr(difference ≤ 0) ≈ 0.98/0.96. Findings were comparable for men and women, for non-hypertensive participants, and with adjustment for antihypertensive treatment. Our findings from data on US population samples indicate broad generalizability of OMNIHEART results beyond the trial setting, and support recommendations for an OMNIHEART-style diet for prevention/control of population-wide adverse BP levels.

Blood pressure differences associated with Optimal Macronutrient Intake Trial for Heart Health (OMNIHEART)-like diet compared with a typical American diet

The Dietary Approaches to Stop Hypertension-Sodium (DASH-Sodium) trial demonstrated beneficial effects on blood pressure (BP) of the DASH diet with lower sodium intake when compared with typical American diet. The subsequent Optimal Macronutrient Intake Trial for Heart Health (OMNIHEART) trial reported additional BP benefits from replacing carbohydrate in the DASH diet with either protein or monounsaturated fats. The primary aim of this study is to assess possible BP benefits of an OMNIHEART-like diet in free-living Americans using cross-sectional US population data of the International Study of Macronutrients, Micronutrients and Blood Pressure (INTERMAP) study. The INTERMAP data include four 24-hour dietary recalls, 2 timed 24-hour urine collections, 8 BP readings for 2195 individuals aged 40 to 59 years from 8 US INTERMAP population samples. Analyses are conducted using 2 approaches: (1) regression of BP on a linear OMNIHEART nutrient score calculated for each individual and (2) a Bayesian approach comparing estimated BP levels of an OMNIHEART-like nutrient profile with a typical American nutrient profile. After adjustment for potential confounders, an OMNIHEART score higher by 1 point was associated with systolic/diastolic BP differences of −1.0/−0.5 mm Hg (both P<0.001). Mean systolic/diastolic BPs were 111.3/68.4 and 115.2/70.6 mm Hg for Bayesian OMNIHEART and Control profiles, respectively, after controlling for possible confounders, with BP differences of −3.9/−2.2 mm Hg, P(difference ⩽0)=0.98/0.96. Findings were comparable for men and women, for nonhypertensive participants, and with adjustment for antihypertensive treatment. Our findings from data on US population samples indicate broad generalizability of OMNIHEART results beyond the trial setting and support recommendations for an OMNIHEART-style diet for prevention/control of population-wide adverse BP levels.The DASH-Sodium trial demonstrated beneficial effects on blood pressure (BP) of the DASH diet with lower sodium intake compared to typical American diet. The subsequent OMNIHEART trial reported additional BP benefits from replacing carbohydrate in the DASH diet with either protein or monounsaturated fats. The primary aim of this study is to assess possible BP benefits of an OMNIHEART-like diet in free-living Americans using cross-sectional U.S. population data of the INTERMAP Study. INTERMAP data include four 24-h dietary recalls, two timed 24-h urine collections, eight BP readings for 2,195 individuals ages 40-59 from eight US INTERMAP population samples. Analyses are conducted using two approaches: 1. Regression of BP on a linear OMNIHEART nutrient score calculated for each individual, and 2. A Bayesian approach comparing estimated BP levels of an OMNIHEART-like nutrient profile with a typical American nutrient profile. After adjustment for potential confounders, an OMNIHEART score higher by one point was associated with systolic/diastolic BP differences of −1.0/−0.5 mmHg (both P<0.001). Mean systolic/diastolic BPs were 111.3/68.4 and 115.2/70.6 mmHg for Bayesian OMNIHEART and Control profiles respectively, after controlling for possible confounders, with BP differences of −3.9/−2.2 mmHg, Pr(difference ≤ 0) ≈ 0.98/0.96. Findings were comparable for men and women, for non-hypertensive participants, and with adjustment for antihypertensive treatment. Our findings from data on US population samples indicate broad generalizability of OMNIHEART results beyond the trial setting, and support recommendations for an OMNIHEART-style diet for prevention/control of population-wide adverse BP levels.

Blood Pressure Differences Associated with OMNIHEART-Like Diet Compared to a Typical American Diet

The Dietary Approaches to Stop Hypertension-Sodium (DASH-Sodium) trial demonstrated beneficial effects on blood pressure (BP) of the DASH diet with lower sodium intake when compared with typical American diet. The subsequent Optimal Macronutrient Intake Trial for Heart Health (OMNIHEART) trial reported additional BP benefits from replacing carbohydrate in the DASH diet with either protein or monounsaturated fats. The primary aim of this study is to assess possible BP benefits of an OMNIHEART-like diet in free-living Americans using cross-sectional US population data of the International Study of Macronutrients, Micronutrients and Blood Pressure (INTERMAP) study. The INTERMAP data include four 24-hour dietary recalls, 2 timed 24-hour urine collections, 8 BP readings for 2195 individuals aged 40 to 59 years from 8 US INTERMAP population samples. Analyses are conducted using 2 approaches: (1) regression of BP on a linear OMNIHEART nutrient score calculated for each individual and (2) a Bayesian approach comparing estimated BP levels of an OMNIHEART-like nutrient profile with a typical American nutrient profile. After adjustment for potential confounders, an OMNIHEART score higher by 1 point was associated with systolic/diastolic BP differences of −1.0/−0.5 mm Hg (both P<0.001). Mean systolic/diastolic BPs were 111.3/68.4 and 115.2/70.6 mm Hg for Bayesian OMNIHEART and Control profiles, respectively, after controlling for possible confounders, with BP differences of −3.9/−2.2 mm Hg, P(difference ⩽0)=0.98/0.96. Findings were comparable for men and women, for nonhypertensive participants, and with adjustment for antihypertensive treatment. Our findings from data on US population samples indicate broad generalizability of OMNIHEART results beyond the trial setting and support recommendations for an OMNIHEART-style diet for prevention/control of population-wide adverse BP levels.The DASH-Sodium trial demonstrated beneficial effects on blood pressure (BP) of the DASH diet with lower sodium intake compared to typical American diet. The subsequent OMNIHEART trial reported additional BP benefits from replacing carbohydrate in the DASH diet with either protein or monounsaturated fats. The primary aim of this study is to assess possible BP benefits of an OMNIHEART-like diet in free-living Americans using cross-sectional U.S. population data of the INTERMAP Study. INTERMAP data include four 24-h dietary recalls, two timed 24-h urine collections, eight BP readings for 2,195 individuals ages 40-59 from eight US INTERMAP population samples. Analyses are conducted using two approaches: 1. Regression of BP on a linear OMNIHEART nutrient score calculated for each individual, and 2. A Bayesian approach comparing estimated BP levels of an OMNIHEART-like nutrient profile with a typical American nutrient profile. After adjustment for potential confounders, an OMNIHEART score higher by one point was associated with systolic/diastolic BP differences of −1.0/−0.5 mmHg (both P<0.001). Mean systolic/diastolic BPs were 111.3/68.4 and 115.2/70.6 mmHg for Bayesian OMNIHEART and Control profiles respectively, after controlling for possible confounders, with BP differences of −3.9/−2.2 mmHg, Pr(difference ≤ 0) ≈ 0.98/0.96. Findings were comparable for men and women, for non-hypertensive participants, and with adjustment for antihypertensive treatment. Our findings from data on US population samples indicate broad generalizability of OMNIHEART results beyond the trial setting, and support recommendations for an OMNIHEART-style diet for prevention/control of population-wide adverse BP levels.

Examining the Association between Deprivation Profiles and Air Pollution in Greater London using Bayesian Dirichlet Process Mixture Models

Standard regression analyses are often plagued with problems encountered when one tries to make inference going beyond main effects, using datasets that contain dozens of variables that are potentially correlated. This situation arises, for example, in environmental deprivation studies, where a large number of deprivation scores are used as covariates, yielding a potentially unwieldy set of interrelated data from which teasing out the joint effect of multiple deprivation indices is difficult. We propose a method, based on Dirichlet-process mixture models that addresses these problems by using, as its basic unit of inference, a profile formed from a sequence of continuous deprivation measures. These deprivation profiles are clustered into groups and associated via a regression model to an air pollution outcome. The Bayesian clustering aspect of the proposed modeling framework has a number of advantages over traditional clustering approaches in that it allows the number of groups to vary, uncovers clusters and examines their association with an outcome of interest and fits the model as a unit, allowing a region’s outcome potentially to influence cluster membership. The method is demonstrated with an analysis UK Indices of Deprivation and PM10 exposure measures corresponding to super output areas (SOA’s) in greater London.

418 BLOOD PRESSURE DIFFERENCES ASSOCIATED WITH DASH-LIKE LOWER SODIUM COMPARED WITH TYPICAL AMERICAN HIGHER SODIUM NUTRIENT PROFILE: INTERMAP USA

Background: The DASH-Sodium trial demonstrated beneficial effects on blood pressure (BP) of the DASH diet with lower sodium intake, compared to typical American diet with higher sodium. Objective: Assess possible BP benefits of a lower sodium DASH-like diet in free-living Americans using two statistical methods: a linear DASH nutrient score, and a Bayesian approach comparing estimated BP levels for a DASH-like lower sodium nutrient profile (“DASH-Na”) with those for a typical American higher sodium profile (“Control”). Design: Cross-sectional data include four 24-h dietary recalls, two timed 24-h urine collections, eight BP readings for 2,195 individuals ages 40–59 from eight US INTERMAP population samples. A DASH score (9 nutrient targets) was calculated for each participant and regressed on their BP. For Bayesian profile regression, participants were assigned to clusters based on similarity of their nutrient profiles. Pre-specified DASH-Na and Control profiles were also assigned to clusters. Posterior distributions were obtained for mean BP levels associated with DASH-Na and Control profiles. Results: One unit higher DASH score was associated with systolic/diastolic BP lower by 1.2/0.7 mmHg (both P < 0.001). Mean systolic/diastolic BPs were 114.6/71.4 and 122.6/75.4 mmHg for Bayesian DASH-Na and Control profiles respectively; controlled for possible confounders, average BP differences were −4.9/−2.1 mmHg (P = 0.01/0.08). Findings were comparable for men and women, for non-hypertensive participants, and with adjustment for antihypertensive treatment. Conclusions: Our findings from data on US population samples indicate broad generalisability of DASH-Sodium trial results, and support recommendations for a reduced sodium DASH-style diet for prevention/control of population-wide adverse BP levels.