Air Pollution and Serum Glucose Levels: A Population-Based Study

Abstract

Recent studies demonstrated an adverse effect of chronic exposure to air pollution (AP) on metabolic syndrome and its components. In a population-based study, we investigated the association between exposure to ambient AP and serum glucose (SG), among subjects with normal glucose, impaired fasting glucose (IFG), and diabetes mellitus (DM).We included 1,063,887 SG tests performed in 131,882 subjects (years 2001-2012). Exposure data included daily levels of SO2, NO2 and other pollutants of industrial, traffic, and nonanthropogenic sources. Demographical, clinical, and medications purchase data were assessed. Log-transformed SG levels were analyzed by linear mixed models adjusted for seasonal variables and personal characteristics.SG increases (%increase [95% CI]), among subjects with normal glucose, IFG, and DM, respectively, were associated with 6.36 ppb increase of NO2 measured 24 to 72 hours before the test (0.40% [0.31%; 0.50%], 0.56% [0.40%; 0.71%], and 1.08% [0.86%; 1.29%]); and with 1.17 ppb increase of SO2 measured 24 hours before the test (0.29% [0.22%; 0.36%], 0.20% [0.10%; 0.31%], and 0.33% [0.14%; 0.52%]). Among DM population, weakest association was observed among patients treated with Metformin (0.56% increase in SG [0.18%; 0.95%]).In conclusion, NO2 and SO2 exposure is associated with small but significantly increased levels of SG. Although DM patients were found to be more susceptible to the AP induced SG variations, Metformin treatment seem to have a protective effect. Given the chronic lifetime exposure to AP and the broad coverage of the population, even small associations such as those found in our study can be associated with detrimental health effects and may have profound public health implications.

FIGURE 1

The total number of tests and subjects included in the study, by 3 comparison groups: subjects with normal glucose, impaired fasting glucose (IFG), and diabetes mellitus (DM). DM patients are stratified by the treatment type.

FIGURE 2

The percent change in serum glucose levels for IQR elevation of NO₂ (6.36 ppb) and SO₂ (1.17 ppb) concentration 72 hours before the test, with 95% confidence intervals. The coefficients were back-transformed using the following formula: EXP ((β^∗IQR) − 1)×100. Where EXP = exponential value, β = the regression coefficient, and IQR = the pollutants’ interquartile range. Models were performed separately among untreated patients with diabetes, and among patients treated with Insulin, Metformin, or other antidiabetic medications. Models were adjusted for day of the week, year, average temperature and relative humidity, gender, age, ethnicity, socioeconomic status, hypertension, and the purchase of antidiabetic medications 3 months before the test. IQR = interquartile range; ^∗P < 0.05.