Use of the Adaptive LASSO Method to Identify PM(2.5) Components Associated with Blood Pressure in Elderly Men: The Veterans Affairs Normative Aging Study

BACKGROUND: PM(2.5) (particulate matter ≤ 2.5 μm) has been associated with adverse cardiovascular outcomes, but it is unclear whether specific PM(2.5) components, particularly metals, may be responsible for cardiovascular effects. OBJECTIVES: We aimed to determine which PM(2.5) components are associated with blood pressure in a longitudinal cohort. METHODS: We fit linear mixed-effects models with the adaptive LASSO penalty to longitudinal data from 718 elderly men in the Veterans Affairs Normative Aging Study, 1999–2010. We controlled for PM(2.5) mass, age, body mass index, use of antihypertensive medication (ACE inhibitors, non-ophthalmic beta blockers, calcium channel blockers, diuretics, and angiotensin receptor antagonists), smoking status, alcohol intake, years of education, temperature, and season as fixed effects in the models, and additionally applied the adaptive LASSO method to select PM(2.5) components associated with blood pressure. Final models were identified by the Bayesian Information Criterion (BIC). RESULTS: For systolic blood pressure (SBP), nickel (Ni) and sodium (Na) were selected by the adaptive LASSO, whereas only Ni was selected for diastolic blood pressure (DBP). An interquartile range increase (2.5 ng/m(3)) in 7-day moving-average Ni was associated with 2.48-mmHg (95% CI: 1.45, 3.50 mmHg) increase in SBP and 2.22-mmHg (95% CI: 1.69, 2.75 mmHg) increase in DBP, respectively. Associations were comparable when the analysis was restricted to study visits with PM(2.5) below the 75th percentile of the distribution (12 μg/m(3)). CONCLUSIONS: Our study suggested that exposure to ambient Ni was associated with increased blood pressure independent of PM(2.5) mass in our study population of elderly men. Further research is needed to confirm our findings, assess generalizability to other populations, and identify potential mechanisms for Ni effects. CITATION: Dai L, Koutrakis P, Coull BA, Sparrow D, Vokonas PS, Schwartz JD. 2016. Use of the adaptive LASSO method to identify PM(2.5) components associated with blood pressure in elderly men: the Veterans Affairs Normative Aging Study. Environ Health Perspect 124:120–125; http://dx.doi.org/10.1289/ehp.1409021