Bad Air and Blood Sugar? Study Attempts to Link Pollution and Diabetes Risk

September 16, 2016

Higher levels of nitrogen dioxide were associated with higher levels of HOMA-IR, glucose, insulin, and leptin. The degree of association, however, varied among the different populations. Effect estimates for pre-diabetic individuals were large and highly statistically significant, while the associations were smaller and weaker in non-diabetic individuals and those who had already developed T2DM.

A new analysis of health and air-quality data from southern Germany suggests that pollution increases the risk that prediabetes will progress to type 2 diabetes mellitus (T2DM).

Investigators used linear regression models to look for associations in 2,944 patients between local pollution and fasting samples of insulin resistance (HOMA-IR), glucose, insulin, HbA1c, leptin, and C-reactive protein (hs-CRP). Effect estimates were calculated for the whole study population as well as non-diabetic, pre-diabetic and diabetic individuals

Among the whole study population, a 7.9μg/m3 increment in particulate matter <10μm was associated with significantly higher levels of HOMA-IR (15.6% increase; 95% confidence interval [CI], 4.0%-28.6%) and insulin (14.5%; 95% CI, 3.6%-26.5%).

Higher levels of nitrogen dioxide were associated with higher levels of HOMA-IR, glucose, insulin, and leptin. The degree of association, however, varied among the different populations. Effect estimates for pre-diabetic individuals were large and highly statistically significant, while the associations were smaller and weaker in non-diabetic individuals and those who had already developed T2DM.

The study authors, who published their findings in Diabetes, found no significant association between pollution levels and HbA1c.

“The results revealed that people who already have an impaired glucose metabolism — so-called pre-diabetic individuals — are particularly vulnerable to the effects of air pollution,” said Kathrin Wolf, MD, the lead author of the study. “In these individuals, the association between increases in their blood marker levels and increases in air pollutant concentrations is particularly significant. Thus, over the long term — especially for people with impaired glucose metabolism — air pollution is a risk factor for type 2 diabetes.”

Most of the pollution the investigators studied stemmed from automotive traffic around the city of Düsseldorf. Patients who lived near the center of the city were exposed to considerably more pollutants than those who lived in the suburbs or in rural areas.

“Whether type 2 diabetes becomes manifest and when this occurs is not only due to lifestyle or genetic factors, but also due to traffic-related air pollution,” said Annette Peters, PhD, a study co-author who is director of the Institute of Epidemiology II at Helmholtz Zentrum München and head of the epidemiology at the German Center for Diabetes Research. “A precise knowledge of the risk factors is crucial for counteracting the increasing incidence of diabetes.”

The new study is not the first to link air pollution and diabetes. A 2012 research review that appeared in Diabetes reported that there were at least 6 epidemiologic studies showing some degree of association between traffic-related air pollution and some type of diabetes. (Most of the studies did not distinguish between type 1 and type 2.) Several of the studies found a greater positive connection between pollution and diabetes in women than in men.

“The sex-specific differences seen in some of these studies may relate to true differences in biologic susceptibility, a finding mirrored by observations in the Women’s Health Study that also demonstrated a greater susceptibility of obese women to air pollution—mediated cardiovascular events," the review authors wrote. “In contrast, it is also possible that the sex predilection may relate to exposure assessment error, particularly in males, who tend to be more mobile compared with females.”

The review authors noted that there is also experimental evidence demonstrating that exposure to particulate matter increases the risk of incident T2DM in mice.

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