Longitudinal Associations of Air Pollution With Body Size and Composition in Midlife Women: The Study of Women’s Health Across the Nation

OBJECTIVE We examined longitudinal associations of air pollution exposure, including fine particulate matter (PM_2.5), nitrogen dioxide (NO₂), and ozone (O₃), with weight, BMI, waist circumference, fat mass, lean mass, and proportion fat mass in midlife women. RESEARCH DESIGN AND METHODS The study population included 1,654 White, Black, Chinese, and Japanese women from the Study of Women’s Health Across the Nation, with the baseline median age of 49.6 years, followed from 2000 to 2008. Annual air pollution exposures were assigned by linking residential addresses with hybrid estimates of air pollut-ant concentrations at 1-km² resolution. Body size was measured, and body composition was measured using DXA at approximately annual visits. Linear mixed effects models were used to examine the associations between air pollution and body size and composition measures and whether these associations differed by physical activity. RESULTS After adjusting for potential confounders, an interquartile range increase in PM_2.5 concentration (4.5 lg/m³ ) was associated with 4.53% (95% CI 3.85%, 5.22%) higher fat mass, 1.10% (95% CI 0.95%, 1.25%) higher proportion fat mass, and 0.39% (95% CI 20.77%, 20.01%) lower lean mass. Similar associations were also observed for NO₂ and O₃. Weaker associations of PM_2.5 and NO₂ with body composition were observed in participants who engaged in more physical activity. CONCLUSIONS Our analyses provide evidence that exposure to PM_2.5, NO₂, and O₃, is adversely associated with body composition, including higher fat mass, higher proportional fat mass, and lower lean mass, highlighting their potential contribution to obesity.