Long-term exposure to air pollution may increase the risk of developing type 2 diabetes - especially for people with impaired glucose metabolism, a new study has warned. Air pollution exposure at the place of residence increases the risk of developing insulin resistance as a pre-diabetic state of type 2 diabetes, researchers said. "Whether the disease becomes manifest and when this occurs is not only due to lifestyle or genetic factors, but also due to traffic-related air pollution," said Professor Annette Peters, director of the Institute of Epidemiology II at Helmholtz Zentrum Munchen in Germany. For the current study, Peters and her colleagues from the German Centre for Diabetes Research (DZD) analysed the data of nearly 3,000 participants of the Cooperative Health Research in the Region of Augsburg (KORA) study who live in the city of Augsburg and two adjacent rural counties. All individuals were interviewed and physically examined. The researchers took fasting blood samples, in which they determined various markers for insulin resistance and inflammation. In addition, leptin was examined as adipokine which has been suggested to be associated with insulin resistance. Non-diabetic individuals underwent an oral glucose tolerance test to detect whether their glucose metabolism was impaired. The researchers compared these data with the concentrations of air pollutants at the place of residence of the participants, which they estimated using predictive models based on repeated measurements at 20 sites (for particle measurements) and at 40 sites (for nitrogen dioxide measurements) in the city and in the rural counties. "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 Dr Kathrin Wolf, 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," said Wolf. The research was published in the journal Diabetes.