Date Published: 31 January 2014

Obese children more likely to suffer from asthma as a result of air pollution

Recent research from Columbia University Medical Center (NY, USA) indicates that obese children exposed to high levels of air pollutants are almost three times as likely to have asthma, compared with non-obese children and lower levels of pollution.

What is obesity ?
There are two common definitions of obesity, which are:

1. A person has a weight at least 20% above the recommended weight (for his or her height and gender), and
2. A person's body mass index (BMI) is over 30.

In order for a person to be considered obese, either of these conditions may apply - not necessarily both, although that is often the case. For more detail see what is obesity?

According to the recent (US-based) study, rates of childhood obesity and asthma have both increased dramatically in the past 30 years. Statistics cited by the researchers include an increase in the percentage of American children who are obese, from 7% 1980 to 20% in 2008. Childhood asthma has also increased, more than doubling in percentage terms during approximately the same period, from 4% in 1980 to 10% in 2009.

Researchers from Columbia University Medical Center followed 311 children in predominantly Dominican and African-American neighborhoods of New York City. They monitored indoor air in each child's home for two weeks at age 5 or 6, to measure exposure to a family of air pollutants, polycyclic aromatic hydrocarbons (PAHs). The child's height and weight were measured and respiratory questionnaires were administered. 20% were found to have asthma and 20% were found to be obese according to a definition using body mass index (BMI).

It was found that high levels of airbourne pollutants (exposure to polycyclic aromatic hydrocarbons) was associated with asthma only among obese children. In particular, the association was with the alkylated forms of polycyclic aromatic hydrocarbons, which are emitted by vehicles, cigarette smoke, cooking, incense, burning candles, and various other indoor sources. A two- to three-fold increase in asthma risk was observed 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 asthma," says lead author Kyung Hwa Jung, PhD, associate research scientist in the Department of Medicine at Columbia University College of Physicians and Surgeons (P&S).

" 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," said senior author Rachel Miller, MD, associate professor of medicine and environmental health sciences (in pediatrics), 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.

However, the precise way in which exposure to these air pollutants combine with obesity to increase risk of asthma is not known. One theory is that sedentary lifestyle in obese children could result in more time spent indoors, increasing exposure to indoor PAH. Alternatively, the rapid breathing associated with obesity may be significant.

This study added to information accrued from previous research that linked increased asthma risk with exposure to higher levels of air pollution. Drs. Jung and Miller previously had shown an association between repeated high prenatal and childhood PAH exposure and asthma. Previous studies also have shown an association between obesity and asthma. It seems that more research is needed in order to improve understanding of the risk factors for childhood asthma, including how such risk factors are inter-related.

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