Three Ways Pollution May Add to Obesity

A growing body of evidence links pollution exposure to an elevated risk of obesity. Two recent studies provide both insight into the mechanisms and population-based evidence for the connection.

Varying levels of air pollution in 25 districts of northeastern China created a natural experiment for testing the relationship with obesity. Recently in Obesity, Guang-Hui Dong and colleagues published a study of more than 30,000 children, recording height, weight, exposure to various forms of polution, and other variables. They found an association between air pollution exposure and obesity that might be explained by any of three factors.

1. Immune Response. Insulin resistance has been shown to be the end result of inflammatory responses to air pollution. These responses are best documented with small particle air pollution. But the present study also saw a significant relationship with sulfur dioxide, ozone, and nitrogen dioxide. More research is needed to document the pathways for insulin resistance in response to those three pollutants.
    
2. Birth Weight. Another explanation for the link between obesity and air pollution in this study could be effects on infant birth weights and compensatory growth patterns that lead to obesity. Ambient air pollution is well-understood to lead to low birth weights. And low birth weights are linked to compensatory growth and subsequent childhood obesity.
    
3. Physical Activity. Children in areas of high air pollution might find their opportunities for physical activity constrained by the adverse conditions in which they live. Parents may well keep their children inside to protect them from exposure to polluted outdoor air.

 
Persistent organic pollutants (POPs) are another source of pollution suspected of playing a role in obesity risk. Scientists from the Institut de recherches cliniques de Montreal studied a group of women with similar physical characteristics, including BMI, age, and fat mass. They did find differences in their exposure to POPs that correlated closely with the presence or absence of cardiometabolic disease. Women exposed to higher levels of POPs were found to be at greater risk for cardiometabolic disease than others, even though they had similar levels of adiposity. The study was published in the Journal of Endocrinology and Metabolism.

This growing body of evidence suggests we must deal with the physiological basis for obesity that goes far beyond eating and exercise habits. “Let’s move!” is great advice, but it might not be enough by itself to reverse the effects of potent biological factors we scarcely understand.

Click here to read the study of air pollution in China, click here to read about the study of POPs, and click here to read the study itself.

Pollution Buttons, photograph © arbyreed / flickr

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