Obesity risk in middle-aged women linked to air pollution in new study

Nearly 42% of adults in the U.S. are now considered to have obesity, but there's no easy explanation why. After all, many contributing elements determine a person's weight, including genetics, muscle mass, diet, exercise routine and environmental factors. But a new study found one surprising contributor to weight, as far as women are concerned: air pollution.

The study, which was published in the journal of the American Diabetes Association, Diabetes Care, analyzed data from 1,654 women from the Study of Women’s Health Across the Nation, a multi-site, long-term study designed to examine the health of women during their middle years. Data collected from the women, who had a median age of 49.6, included body size and body composition. The researchers also tracked annual air pollution exposures.

Here's what they found: The more air pollution the women were exposed to, the greater their risk of developing obesity. Air pollution exposure was specifically linked to higher body fat, a higher proportion of fat and a lower lean body mass in women who are in their middle years. Women exposed to air pollution had an increase in body fat of 4.5% or about 2.6 pounds.

The researchers also looked at how air pollution and physical activity influenced body composition and found that high levels of physical activity were a good way to offset exposure to air pollution.

The lead author of the study, Xin Wang, a research investigator in the Department of Epidemiology at the University of Michigan School of Public Health, tells Yahoo Life that he and his team wanted to identify and study "modifiable risk factors, including exposures to environmental pollutants," to help identify people who are at high risk for having obesity.

Wang says it's not surprising that air pollution may play a role in the development of obesity. "If we look at history, it is not hard to find that the fast rise in obesity prevalence has paralleled the increasing exposure to environmental pollutants," he says. Wang notes that research has already linked exposure to air pollution—including fine particulate matter, nitrogen dioxide and ozone — to increases in inflammation of fat tissue, along with a slew of other factors that are "tightly linked to obesity."

It's easy to assume that air pollution could increase a person's chances of developing obesity because it keeps people indoors, but it's more complex than that, Dr. Fatima Cody Stanford, an obesity medicine physician and clinical researcher at Massachusetts General Hospital, tells Yahoo Life. "Research shows that it appears that air pollution may lead to metabolic dysfunction — meaning, it affects your metabolism and how your body stores cholesterol," Stanford says. "Air pollution also seems to be tied to chronic disease onset, whether it's diabetes or obesity."

But, she adds, "when you have air pollution, of course it can disrupt regularly physical activity, particularly in an outdoor setting."

As for exercise helping to combat the impact of air pollution on weight, that is correlated with the benefits of exercise in general, Dr. Mark Conroy, an emergency medicine physician at The Ohio State University Wexner Medical Center, tells Yahoo Life. "Exercise has long been viewed as having a strong association with improved health and body composition," he says. "In individuals with high levels of inflammation, exercise can lower those levels, improve metabolism and promote fat loss."

Stanford cautions against blaming obesity on air pollution alone. "Obesity is a complex, multifactorial relapsing-remitting disease," she says. "Everyone that has obesity may have it for a variety of different reasons. For some, air pollution may be one of the things that leads to some of the disease that people have but, for many, there are multiple factors that play a role." She lists among these family history, medications and chronic stress. "It's important for us not to just single out one factor as being the reason why people have obesity," she says.

Wang points out that the study was conducted on a specific population — midlife women who were exposed to a specific range of air pollution (the median annual PM2.5 concentration ranged from 12.3 μg/m3 to 15.9 μg/m3). As a result, it's not possible to conclude that the findings apply to everyone. "However, our findings call for more studies, especially those with high exposed population, to confirm the association between air pollution and obesity," he says. "This will help find out whether air pollution is an important contributor to the epidemic of obesity and establish the foundation for future studies for intervention strategies."

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