Polluted Air Increases Obesity Risk in Young Animals

Exposure to polluted air early in life led to an accumulation of abdominal fat and insulin resistance in mice even if they ate a normal diet, according to new research.

Animals exposed to the fine-particulate air pollution had larger and more fat cells in their abdominal area and higher blood sugar levels than did animals eating the same diet but breathing clean air.

Researchers exposed the mice to the polluted air for six hours a day, five days a week for 10 weeks beginning when the animals were 3 weeks old. This time frame roughly matches the toddler years to late adolescence in humans.

The exposure levels for the animals subjected to polluted air resemble the fine-particulate pollution that can be found in urban areas in the United States.

“This is one of the first, if not the first, study to show that these fine particulates directly cause inflammation and changes in fat cells, both of which increase the risk for Type 2 diabetes,” said Qinghua Sun, an associate professor of environmental health sciences at Ohio State University and lead author of the study.

The research appears in the December issue of the journal Arteriosclerosis, Thrombosis, and Vascular Biology.

Sun and colleagues fed the mice with either a normal diet or a high-fat diet and exposed them to either filtered air or air containing at least seven times more fine particulates than the ambient air in Columbus, Ohio. On average, the ambient air contained 15.8 micrograms of fine particles per cubic meter, compared to 111 micrograms per cubic meter in the concentrated air to which the mice were exposed.

According to the U.S. Environmental Protection Agency, roughly one out of every three people in the United States is at a higher risk of experiencing health effects related to the presence of polluted air. Because of their tiny size – 2.5 micrometers or smaller in diameter, or about 1/30th of the average width of a human hair – these particles could reach deep areas of the lungs and other organs in the body.

For this study, researchers obtained baseline measures of the mice for their weight, blood sugar and body fat at the start of the experiment. After exposing the animals to polluted or filtered air for 10 weeks, researchers analyzed the mice for a number of risk factors associated with obesity and insulin resistance, the hallmark of Type 2 diabetes.

As expected, mice on the high-fat diet gained much more weight than those on the normal diet. But mice exposed to polluted air and eating the normal diet had more significant elevations in glucose – sugar in their blood – than did normal-diet mice that breathed clean air. They also showed more signs of insulin resistance based on an index that measures both sugar and insulin in the blood at the same time.

Insulin resistance results when the presence of insulin does not initiate the transfer of glucose from the blood into the tissues, where it is used for energy.