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Lipid adjustment for chemical exposures: accounting for concomitant variables.

ABSTRACT: Some environmental chemical exposures are lipophilic and need to be adjusted by serum lipid levels before data analyses. There are currently various strategies that attempt to account for this problem, but all have their drawbacks. To address such concerns, we propose a new method that uses Box-Cox transformations and a simple Bayesian hierarchical model to adjust for lipophilic chemical exposures.We compared our Box-Cox method to existing methods. We ran simulation studies in which increasing levels of lipid-adjusted chemical exposure did and did not increase the odds of having a disease, and we looked at both single-exposure and multiple-exposure cases. We also analyzed an epidemiology dataset that examined the effects of various chemical exposure on the risk of birth defects.Compared with existing methods, our Box-Cox method produced unbiased estimates, good coverage, similar power, and lower type I error rates. This was the case in both single- and multiple-exposure simulation studies. Results from analysis of the birth-defect data differed from results using existing methods.Our Box-Cox method is a novel and intuitive way to account for the lipophilic nature of certain chemical exposures. It addresses some of the problems with existing methods, is easily extendable to multiple exposures, and can be used in any analysis that involves concomitant variables.

SUBMITTER: Li D

PROVIDER: S-EPMC3812826 | biostudies-literature | 2013 Nov

REPOSITORIES: biostudies-literature

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Lipid adjustment for chemical exposures: accounting for concomitant variables.

Li Daniel D Longnecker Matthew P MP Dunson David B DB

Epidemiology (Cambridge, Mass.) 20131101 6

<h4>Background</h4>Some environmental chemical exposures are lipophilic and need to be adjusted by serum lipid levels before data analyses. There are currently various strategies that attempt to account for this problem, but all have their drawbacks. To address such concerns, we propose a new method that uses Box-Cox transformations and a simple Bayesian hierarchical model to adjust for lipophilic chemical exposures.<h4>Methods</h4>We compared our Box-Cox method to existing methods. We ran simul ...[more]

PMID: 24051893

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Project description:BackgroundThe impact of nitrogen dioxide (NO2) and particulate matter with an aerodynamic diameter of less than or equal to 2.5. microns (PM2.5) exposures on lung function has been investigated mainly in children and less in adults. Furthermore, it is unclear whether short-term deviations of air pollutant concentration need to be considered in long-term exposure models.ObjectivesThe aims of this study were to investigate the association between short-term air pollution exposure and lung function and to assess whether short-term deviations of air pollutant concentration should be integrated into long-term exposure models.MethodsShort-term (daily averages 0-7 d prior) and long-term (1- and 4-y means) NO2 and PM2.5 concentrations were modeled using satellite, land use, and meteorological data calibrated on ground measurements. Forced expiratory volume within the first second (FEV1) of forced exhalation and forced vital capacity (FVC) were measured during a LuftiBus assessment (2003-2012) and linked to exposure information from the Swiss National Cohort for 36,085 adults (ages 18-95 y). We used multiple linear regression to estimate adjusted associations, and additionally adjusted models of long-term exposures for short-term deviations in air pollutant concentrations.ResultsA 10μg/m3 increase in NO2 and PM2.5 on the day of the pulmonary function test was associated with lower FEV1 and FVC (NO2: FEV1 -8.0 ml [95% confidence interval: -13.4, -2.7], FVC -16.7 ml [-23.4, -10.0]; PM2.5: FEV1 -15.3 ml [-21.9, -8.7], FVC -18.5 ml [-26.5, -10.5]). A 10μg/m3 increase in 1-y mean NO2 was also associated with lower FEV1 (-7.7 ml; -15.9, 0.5) and FVC (-21.6 ml; -31.9, -11.4), as was a 10μg/m3 increase in 1-y mean PM2.5 (FEV1: -42.2 ml; -56.9, -27.5; FVC: -82.0 ml; -100.1, -63.9). These associations were robust to adjustment for short-term deviations in the concentration of each air pollutant.ConclusionsShort- and long-term air pollution exposures were negatively associated with lung function, in particular long-term PM2.5 exposure with FVC. Our findings contribute substantially to the evidence of adverse associations between air pollution and lung function in adults. https://doi.org/10.1289/EHP7529.

Project description:Background and purposeExpert consensus guidelines recommend low-density lipoprotein cholesterol as the primary serum lipid target for recurrent stroke risk reduction. However, mounting evidence suggests that other lipid parameters might be additional therapeutic targets or at least also predict cardiovascular risk. Little is known about the effects of nontraditional lipid variables on recurrent stroke risk.MethodsWe analyzed the Vitamin Intervention for Stroke Prevention study database comprising 3680 recent (<120 days) noncardioembolic stroke patients followed up for 2 years. Independent associations of baseline serum lipid variables with recurrent ischemic stroke (primary outcome) and the composite end point of ischemic stroke/coronary heart disease/vascular death (secondary outcomes) were assessed.ResultsOf all variables evaluated, only triglycerides/high-density lipoprotein cholesterol (HDL-C) ratio was consistently and independently related to both outcomes: compared with the lowest quintile, the highest triglycerides/HDL-C ratio quintile was associated with stroke (adjusted hazard ratio, 1.56; 95% confidence interval, 1.05-2.32) and stroke/coronary heart disease/vascular death (1.39; 1.05-1.83), including adjustment for lipid modifier use. Compared with the lowest quintile, the highest total cholesterol/HDL-C ratio quintile was associated with stroke/coronary heart disease/vascular death (1.45; 1.03-2.03). Low-density lipoprotein cholesterol/HDL-C ratio, non-HDL-C, elevated triglycerides alone, and low HDL-C alone were not independently linked to either outcome.ConclusionsOf various nontraditional lipid variables, elevated baseline triglycerides/HDL-C and total cholesterol/HDL-C ratios predict future vascular risk after a stroke, but only elevated triglycerides/HDL-C ratio is related to risk of recurrent stroke. Future studies should assess the role of triglycerides/HDL-C as a potential therapeutic target for global vascular risk reduction after stroke.

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Lipid adjustment for chemical exposures: accounting for concomitant variables.

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Lipid adjustment for chemical exposures: accounting for concomitant variables.

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