Exposure to air pollution while in the womb may increase a child's risk of obesity, a new study suggests.
Pregnant women exposed to high levels of polycyclic aromatic hydrocarbons had children who were 1.8 times more likely to be obese at age 5, and 2.3 times more likely to be obese at age 7, than children of women exposed to low levels of those pollutants, according to the researchers.
Polycyclic aromatic hydrocarbons (PAHs) are common air pollutants released by the burning of coal, diesel, oil and gas. PAHs are also present in cigarette smoke.
While children's high-fat diets and lack of physical activity are likely the main causes of childhood obesity, exposure to certain chemicals may contribute to obesity risk by disrupting hormone function and altering the body's metabolism, the researchers said.
"For many people who don't have the resources to buy healthy food or don't have the time to exercise, prenatal exposure to air pollution may tip the scales, making them even more susceptible to obesity," study researcher Andrew Rundle, a professor of epidemiology at Columbia University's Mailman School of Public Health, said in a statement.
However, the study found only an association, and not a cause-effect link, so more research is needed to confirm the findings.
Pollution and obesity
The study involved about 700 pregnant women in New York City who identified themselves as African- American or Dominican. The women lived in areas of northern Manhattan or the South Bronx that are predominantly low-income.
The women's exposure to PAHs was measured with special backpacks designed to sample the surrounding air. The women wore the backpacks for two days during their third trimester. None of the women was a smoker.
The researchers looked at the children born to the women, following up with 422 of them until age 5, and 341 children until age 7.
The results showed that 21 percent of the children were obese at age 5, and 25 percent were obese at age 7. Obesity was determined by calculating the children's body mass index (BMI), a ratio of height and weight.
The higher the children's exposure to PAHs while in the womb, the greater their risk for obesity. At age 7, children of mothers exposed to the highest levels had 2.4 pounds more of fat mass, on average, compared with children of mothers exposed to the lowest levels.
The results held even after the researchers took into account other factors known to influence children's risk of obesity, such as the mothers' weight during pregnancy, the families' household income, neighborhood poverty rates and families' proximities to highly trafficked roads.
The researchers don't know how much pollution the children were exposed to after they were born. It's possible that exposure to pollution during childhood, and not necessarily in the womb, is responsible for the observed link, the researcher said.
Studies in animals have shown exposure to PAHs causes mice to gain fat, and studies in cells have found the chemicals disrupt the normal breakdown of fats.
Certain fuels release more PAHs than others, and efforts in New York City to take diesel buses off the roads and upgrade oil furnaces so they burn cleaner fuel may help reduce PAH levels, Rundle said.
The study was published online April 13 in the American Journal of Epidemiology. It was funded by the National Institute of Environmental Health Sciences.
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