Exposure to air pollutionincreases the risk of developing insulin resistance as a pre-diabetic state of Type-2 diabetes, the study 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 from Helmholtz ZentrumMuenchen - German Research Centre for Environmental Health, located in Neuherberg, in Germany.

For the study, published in the journal Diabetes, the researchersanalysed data of nearly 3,000 participants of the KORA (Cooperative Health Research in the Region Augsburg conducted in Germany between 2006-2008) study who live in the city of Augsburg and two adjacent rural counties.

All individuals were interviewed and physically examined. Furthermore, the researchers took fasting blood samples, in which they determined various markers for insulin resistance and inflammation.

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," lead author of the study Kathrin Wolf from Helmholtz ZentrumMuenchen said.

"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," Wolf noted.