Pollution is believed to create insulin resistance and chronic inflammation, which leads to obesity and diabetes.
When lab rats had to breathe Beijing’s highly polluted air for 3 to 8 weeks, they gained weight and showed signs of cardiovascular and metabolic damage, according to a study published by scientists from Duke University.
The findings provide more evidence that environmental causes may be one factor in rising rates of diabetes and obesity, both of which are increasing around the world. Pollution is believed to cause inflammation and insulin resistance, and the results of the rat study confirmed this.
“Since chronic inflammation is recognized as a factor contributing to obesity and since metabolic diseases such as diabetes and obesity are closely related, our findings provide clear evidence that chronic exposure to air pollution increases the risk for developing obesity,” said Junfeng “Jim” Zhang, a professor of global and environmental health at Duke University and Duke Kunshan University.
Zhang is a senior author of the paper, which appears in the March issue of the Journal of the Federation of American Societies for Experimental Biology.
Researchers placed pregnant rats and offspring in 2 separate chambers; the first group was directly exposed to outdoor air in Beijing and the second was exposed to filtered air with most of the pollution removed.
It only took 19 days for the lungs and livers of the rats exposed to pollution to show signs of damage. They were heavier and had increased tissue inflammation, with 50% higher low-density lipoprotein (LDL) cholesterol, 46% higher triglycerides, and 97% higher total cholesterol.
Insulin resistance, an indicator of type 2 diabetes, was higher in the rats exposed to pollution than the rats who lived in the cleaner air. This supports earlier research connecting pollution to insulin resistance, which is also a precursor to obesity.
The rats exposed to pollution were much heavier at the end of their pregnancy, even though both were fed the same amount of food. The same was true of the rat offspring, which lived in the same quarters as their mothers.
Effects of pollution exposure were more pronounced at 8 weeks than at 3 weeks, which suggests it may take time for inflammation to occur.
“If translated and verified in humans, these findings will support the urgent need to reduce air pollution, given the growing burden of obesity in today’s highly polluted world,” Zhang said.
Chronic inflammation is a reason why cigarette smoking is now considered a potential cause of type 2 diabetes, and not just a risk factor associated with the disease, according to the CDC.
The Chinese government funded the study.