Study: Secondhand smoke and road pollution contribute to obesity in children more in combination than separately

Diet and physical activity aren't the only causes for the obesity epidemic that is sweeping our nation; a recent study finds that secondhand smoke and roadway pollution are also contributors, Ryan White writes for Reporting on Health.

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Researchers at the University of Southern California have found that secondhand smoke and roadway pollution contribute to body-mass-index increases and obesity in children. The study is published in Environmental Health Perspectives.

?Our findings strengthen emerging evidence that exposure to tobacco smoke and [near-roadway pollution] contribute to development of childhood obesity and suggest that combined exposures may have synergistic effects,? the study?s authors write.
The study collected data on 3,318 students through home questionnaires about tobacco exposure in homes, and scientifically estimated each student's exposure to roadway pollution, White reports. Meanwhile, the student's BMI was measured annually between ages 10 and 18. "BMI levels estimate body fat based on height and weight. ?Normal? weight scores range from 18.5 to 24.9, with higher figures considered overweight and 30 the threshold for obesity"

The study allowed for a long list of "confounding variables," or other factors that might be responsible for these elevated BMIs, including: team sports participation, asthma history, social makeup of family and neighborhood, parents? education, neighborhood walkability, recreation facilities, population density, unemployment rates and so forth, White reports.

"After crunching the data, researchers found that exposure to high levels of roadway pollution alone was associated with average increases of 0.80 BMI units over the eight-year study, while children with secondhand smoke exposure and low roadway pollution averaged 0.85 units higher, compared to similar peers. But when investigators looked at children with high exposures to both tobacco smoke and air pollution, their BMIs were on average 2.15 higher over eight years," White writes.

This is the first study to look at tobacco smoke and air pollution in combination. Other studies have looked at each of these contributors independently and found "secondhand smoke is associated with increased obesity risk in children and patterns of overweight children from mothers who smoked during pregnancy are well documented," White writes. Another study associates "prenatal exposure to roadway pollution with higher BMI and obesity by age 7."

But White notes that socioeconomic status, while ruled out as a "confounder," must still be considered as those who have a lower socioeconomic status are more likely to smoke, live in neighborhoods bisected by busy roadways, have less access to healthy foods and fewer places to exercise.

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