… our results point to an association between traffic-related air pollution and biomarkers related to insulin resistance, subclinical inflammation and adipokines in the general population. The effect estimates were remarkably high for individuals with i-IFG or i-IGT or both suggesting this subgroup to be particularly susceptible for adverse health effects due to air pollution exposure.

—Wolf et al.

For the current study, the team analyzed the data of 2,944 participants of the KORA (Cooperative Health Research in the Region Augsburg) F4 study conducted in southern Germany (2006-2008).

They analyzed associations between individual air pollution concentration estimated by land use regression and HOMA-IR (homeostasis model assessment-estimated insulin resistance), glucose, insulin, HbA_1c (glycated hemoglobin), leptin, and hs-CRP (high-sensitivity C-reactive protein) from fasting samples using multivariable linear regression models. Effect estimates were calculated for the whole study population and subgroups of non-diabetic, pre-diabetic and diabetic individuals.

Among all participants, a 7.9μg/m³ increment in particulate matter <10 μm was associated with higher HOMA-IR (15.6% [95%-CI: 4.0;28.6]) and insulin (14.5% [3.6;26.5]). (HOMA-IR has also been shown to be an independent predictor of cardiovascular disease (CVD) in type 2 diabetes.)

Nitrogen dioxide was associated with HOMA-IR, glucose, insulin, and leptin. Effect estimates for pre-diabetic individuals were much larger and highly statistically significant, while non-diabetic and diabetic individuals showed rather weak associations. No association was seen for HbA_1c.

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. 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.

—Dr. Kathrin Wolf, lead author of the study

The authors are also concerned that the concentrations of air pollutants, though below EU threshold values, are still above the proposed guidelines of the World Health Organization (WHO). As a consequence, they demand changes in government policy. Moreover, the association between increased exposure to air pollution and respiratory and cardiovascular diseases has now been clearly established.

Next, the scientists want to investigate the influence of ultrafine particles.

A previous study of Helmholtz Zentrum München from 2013 showed that ultrafine particulate air pollution increases the risk of insulin resistance in childhood. In a meta-analysis from 2015 the same authors concluded that there is an association between long-term exposure to air pollutants and the development of type 2 diabetes.

Resources

• Kathrin Wolf, Anita Popp, Alexandra Schneider, Susanne Breitner, Regina Hampel, Wolfgang Rathmann, Christian Herder, Michael Roden, Wolfgang Koenig, Christa Meisinger, Annette Peters, KORA-Study Group (2016) “Association between long-term exposure to air pollution and biomarkers related to insulin resistance, subclinical inflammation and adipokines,” Diabetes doi: 10.2337/db15-1567