If you're at risk for diabetes, stay inside when pollution is at its worst.

New research draws a connection between pollution and type 2 diabetes.

RODALE NEWS, EMMAUS, PA—According to the American Diabetes Association, 7.3 percent of the population suffers from type 2 diabetes, and while many people develop the condition as a result of being overweight or obese, increasing research has found that others seem to develop it as a result environmental factors. A new study in the journal Environmental Health Perspectives has found that traffic pollution could be one of the environmental triggers of diabetes, as the pollutants increase inflammation and can make cells more insulin resistant.

THE DETAILS: The study took place in a heavily industrialized region of western Germany. Between 1985 and 1994, 1,775 women were surveyed about their general health, weight, and dietary habits, as well as other habits, such as how they heated their homes and whether they smoked. The researchers also collected blood samples and measured them for C3c, a marker for inflammation in the body. At the same time, the authors set up air-pollution monitoring stations in seven spots within the study region to measure for particulate matter and nitrogen dioxide, a common traffic pollutant. Sixteen years later, the women were contacted again and asked whether a physician had ever diagnosed them with high cholesterol, heart disease, stroke, or diabetes.

A total of 187 of the women were diagnosed with diabetes over the course of the study, and those women were most likely to smoke and to heat their homes using fossil fuels (which can release particulate matter into indoor air). With each one-point increase in the women's exposure to particulate matter pollution, they were 15 percent more likely to have diabetes, and for each point increase in nitrogen dioxide pollution, the risk varied from an additional 15 to 42 percent. The figures held true even after the researchers adjusted for weight, diet, and genetic risk factors. The risk more than doubled in women who lived near busy roads.

WHAT IT MEANS: Diabetes is a major health threat, raising the risk of heart disease, stroke, hypertension, and even dementia. Knowing that air pollution may play a role opens one more avenue for lowering risk. The researchers write that the link most likely has something to do with C3c, the blood protein that indicates inflammation. The women in the study with high C3c levels were more likely to develop type 2 diabetes, and that blood protein tended to exist in higher amounts in women who lived in areas with greater air pollution. One theory is that pollution reacts with immune cells in the lungs and respiratory passages, triggering chronic inflammation. That chronic inflammation, in turn, makes people more susceptible to diabetes and to the damaging effects of air pollution.