Ambient Fine Particulate Matter Air Pollution and Risk of Weight Gain and Obesity in United States Veterans: An Observational Cohort Study

BACKGROUND: Experimental evidence and studies of children and adolescents suggest that ambient fine particulate matter [particulate matter [Formula: see text] in aerodynamic diameter ([Formula: see text])] air pollution may be obesogenic, but the relationship between [Formula: see text] and the risk of body weight gain and obesity in adults is uncertain. OBJECTIVES: Our goal was to characterize the association between [Formula: see text] and the risks of weight gain and obesity. METHODS: We followed 3,902,440 U.S. Veterans from 2010 to 2018 (median 8.1 y, interquartile range: 7.3–8.4) and assigned time-updated [Formula: see text] exposures by linking geocoded residential street addresses with satellite-based estimates of surface-level [Formula: see text] mass (at [Formula: see text] resolution). Associations with [Formula: see text] were estimated using Cox proportional hazards models for incident obesity [body mass index ([Formula: see text]] and a [Formula: see text] increase in weight relative to baseline and linear mixed models for associations with intra-individual changes in BMI and weight. RESULTS: A [Formula: see text] higher average annual [Formula: see text] concentration was associated with risk of incident obesity [[Formula: see text]; [Formula: see text] (95% CI: 1.06, 1.11)] and the risk of a [Formula: see text] ([Formula: see text]) increase in weight [[Formula: see text] (95% CI: 1.06, 1.08)] and with higher intra-individual changes in BMI [[Formula: see text] (95% CI: 0.139, 0.142)] and weight [[Formula: see text] (95% CI: 0.955, 0.981)]. Nonlinear exposure–response models indicated associations at [Formula: see text] concentrations below the national standard of [Formula: see text]. As expected, a negative exposure control (ambient air sodium) was not associated with obesity or weight gain. Associations were consistent in direction and magnitude across sensitivity analyses that included alternative outcomes and exposures assigned at different spatial resolutions. DISCUSSION: [Formula: see text] air pollution was associated with the risk of obesity and weight gain in a large predominantly male cohort of U.S. Veterans. Discussions about health effects of [Formula: see text] should include its association with obesity, and deliberations about the epidemiology of obesity should consider its association with [Formula: see text]. Investigation in other cohorts will deepen our understanding of the relationship between [Formula: see text] and weight gain and obesity. https://doi.org/10.1289/EHP7944