Air Pollutants Associated with Diabetes Prevalence

A new study suggests that individuals exposed long-term to certain air pollutants may have a higher risk of diabetes.

Led by Ann Weaver, PhD, of Fairbanks School of Public Health, Indiana, the investigative team evaluated African American patients enrolled in the Jackson Heart Study, a prospective cohort study aimed at evaluating the etiologies of cardiovascular, renal, and respiratory diseases in this patient population. The team sought to explore associations between pollution and prevalent diabetes risk.

“Given the disproportionate burden of diabetes among African Americans, this study is important in understanding potential adverse health effects of environmental pollutants among this high-risk population,” Weaver and colleagues wrote.

The Study

The team assessed a total of 5301 patients between 21-94 years of age. All patients resided in the tri-county Jackson, Mississippi Metropolitan Statistical Area, where traffic was the major source of ambient air pollution.

All patients completed an in-home interview and clinic visit at study enrollment, followed by a second interview and clinic interview roughly 4 years later.

The investigators looked at mean levels of particulate matter (PM_2.5) and ozone (O₃) as the primary exposures of interest. Levels in participants’ ZIP codes were assessed 1 and 3 years prior to visits 1 and 2.

Diabetes was defined as fasting blood glucose ≥126 mg/dL, HbA1c ≥6.5%, or use of diabetes medications (insulin or oral diabetes medications) at either visit. 

More specifically, incident diabetes was defined as new cases of diabetes at visit 2 (with no prior diagnosis), and prevalent diabetes was defined as diabetes at either visit regardless of prior diabetes status.

Weaver’s team used mixed-effect modified Poisson regression in order to estimate risk ratios (RRs), 95% confidence intervals (CIs), and prevalence ratios (PRs).

The Results

They reported a diabetes prevalence of 21.8% at visit 1 and 33.2.% at visit 2. Furthermore, 12.5% of those without diabetes at visit 1 developed it at the second visit.

They noted that diabetes was generally observed in older and female patients. Those with diabetes also tended to have a higher BMI, were more likely to be physically inactive, and were more likely to have a family history of diabetes.

In terms of the environment, 1-year and 3-year mean concentrations of PM_2.5 were similar between visit 1 (12.2 µg/m3, IQR = 0.8 and 12.4 µg/m3, IQR = 0.4, respectively) and visit 2 (12.1 µg/m3, IQR = 0.8 and 12.3 µg/m3, IQR = 0.5, respectively)

Additionally, at visit 1, 1-year O₃ concentration was at a median of 40.6 (IQR = 2.3) ppb, and 3-year concentration was at a median of 40.9 (IQR = 1.1) ppb. At visit 2, median 1-year concentration was 40.8 ppb (IQR = 2.5), and median 3-year concentration was 42.2 ppb (IQR = 0.7).

“We did not observe evidence of associations between PM_2.5 or O₃ concentrations and prevalent diabetes at visit 1 after adjustment for covariates,” the team wrote. “At visit 2, in fully adjusted models an IQR increase in 1-year PM_2.5 concentration was associated with prevalence of diabetes (PR, 1.08; 95% CI, 1.00-1.17) and an IQR increase in 1-year O₃ concentration was associated with increased prevalence (PR, 1.18; 95% CI, 1.10-1.27) of diabetes.

They also observed that 3-year O₃ concentration was inversely associated with diabetes (PR 0.95; 95% CI, 0.90-1.01) and that an IQR increase in 1-year O₃ concentration correlated with an increase in diabetes incidence (RR, 1.32; 95% CI, 1.08-1.59).

Furthermore, 3-year O₃ concentration was inversely associated with diabetes incidence (RR, 0.88, 95% CI, 0.76-1.02).

As for limitations, the investigators noted that some patients' information were missing at follow-up, thus making it difficult to establish diabetes status. They indicated that other pollutants, external, and internal factors that were not assessed likely play a role in the prevalence of diabetes.

“Further research should investigate the associations between diabetes various pollutants, specifically with long-term O₃ concentrations, in African-American populations,” Weaver and colleagues concluded.

The study, “Associations between air pollution indicators and prevalent and incident diabetes in an African American cohort, the Jackson Heart Study,” was published online in Environmental Epidemiology.