Associations between long-term exposure to air pollution, glycosylated hemoglobin and diabetes

Abstract

Abstract Background Air pollution exposures have been shown to adversely impact health through a number of biological pathways associated with glucose metabolism. However, few studies have evaluated the associations between air pollution and glycosylated hemoglobin (HbA1c) levels. Further, no studies have evaluated these associations in US populations or investigated whether associations differ in diabetic as compared to non-diabetic populations. To address this knowledge gap, we investigated the associations between airborne fine particulate matter (PM 2.5 ) and nitrogen dioxide (NO 2 ) and HbA1c levels in both diabetic and non-diabetic older Americans. We also examined the impact of PM 2.5 and NO 2 on prevalent diabetes mellitus (DM) in this cohort. Methods We used multilevel logistic and linear regression models to evaluate the association between long-term average air pollutant levels and prevalence of DM and HbA1c levels, respectively, among 4121 older (57+ years) Americans enrolled in the National Social Life, Health, and Aging Project between 2005 and 2011. All models adjusted for age, sex, body mass index, smoking status, race, household income, education level, neighborhood socioeconomic status, geographic region, urbanicity and diabetic medication use. We estimated participant-specific exposures to PM 2.5 on a six-kilometer grid covering the conterminous U.S. using spatio-temporal models, and to NO 2 using nearest measurements from the Environmental Protection Agency’s Air Quality System. HbA1c levels were measured for participants in each of two data collection waves from dried blood spots and log-transformed prior to analysis. Participants were considered diabetic if they had HbA1c values ≥ 6.5% or reported taking diabetic medication. Results The prevalence of diabetes at study entry was 22.2% (n = 916) and the mean HbA1c was 6.0 ± 1.1%. Mean one-year moving average PM 2.5 and NO 2 exposures were 10.4 ± 3.0 μg/m 3 and 13.1 ± 7.0 ppb, respectively. An inter-quartile range (IQR, 3.9 μg/m 3 ) increase in one-year moving average PM 2.5 was positively associated with increased diabetes prevalence (prevalence odds ratio, POR 1.35, 95% CI: 1.19, 1.53). Similarly, an IQR (8.6 ppb) increase in NO 2 was also significantly associated with diabetes prevalence (POR 1.27, 95% CI: 1.10, 1.48). PM 2.5 (1.8% ± 0.6%, p 2 (2.0% ± 0.7%, p 2 was significantly associated with HbA1c in non-diabetic participants (0.8% ± 0.2%, p 2 in non-diabetic participants. Conclusions/interpretations In a cohort of older men and women in the United States, PM 2.5 and NO 2 exposures were significantly associated with prevalence of DM and increased HbA1c levels among both non-diabetic and diabetic participants. These associations suggest that air pollution could be a key risk factor for abnormal glucose metabolism and diabetes in the elderly.