Researchers at Columbia University Medical Center (CUMC), including Columbia’s Mailman School of Public Health, have found that obese children exposed to high levels of air pollutants were nearly three times as likely to have asthma, compared with non-obese children and lower levels of pollution exposure.

The study is based on findings that show an increase in childhood obesity and asthma. According to CUMC, rates of childhood obesity and asthma have both increased dramatically in the past 30 years. The percentage of American children who are obese has increased from 7% in 1980 to 20% in 2008. Childhood asthma is up from 4% in 1980 to 10% in 2009. CUMC notes that rates are higher among urban minority populations.

For the study, researchers followed 311 children, ages 5 or 6, in predominantly Dominican and African-American neighborhoods of New York City. The child’s height and weight were measured and respiratory questionnaires were administered. In all, 20% of the children were found to have asthma and 20% were categorized as obese based on body mass index. The investigators also monitored indoor air in each child’s home for two weeks to measure exposure to air pollutants, polycyclic aromatic hydrocarbons (PAH).

The researchers found that high PAH exposure was associated with asthma only among obese children. In particular, the association was with the alkylated forms of PAH, which are emitted by vehicles and by cigarette smoke, cooking, incense, burning candles, and various other indoor sources. A two- to three-fold increase in asthma risk was seen among obese children exposed to high levels of the PAH chemicals 1-methylphenanthrene and 9-methylphenanthrene. Exposure to PAH or obesity alone did not predict asthma.

“Our results suggest that obesity may magnify the effects of these air pollutants, putting children at greater risk for having asthma,” says lead author Kyung Hwa Jung, PhD, associate research scientist in the Department of Medicine at Columbia University College of Physicians and Surgeons.

According to CUMC, the mechanism behind the association between childhood obesity, air pollution and asthma is not well understood. The study’s investigators note that one possible explanation is that sedentary lifestyle in obese children could result in more time spent indoors, thereby increasing exposure to indoor PAH. Another idea is that the association may have to do with more rapid breathing in those who are obese.

“These findings suggest that we may be able to bring down childhood asthma rates by curbing indoor, as well as outdoor, air pollution and by implementing age-appropriate diet and exercise programs,” says senior author Rachel Miller, MD, Professor of Medicine in Pediatrics and Environmental Health Sciences, chief of Pediatric Allergy and Immunology at CUMC, and co-deputy director of the Columbia Center for Children’s Environmental Health at the Mailman School of Public Health.