"Given the epidemic of obesity in children, it might be that we're developing a population that is more susceptible to air pollution," said lead researcher Heike Luttmann-Gibson, Ph.D., of the Harvard School of Public Health in Boston. She and co-researcher Douglas Dockery, Sc.D. studied 611 Boston-area fourth- and fifth-graders who were participating in a study on short-term effects of air pollution.

They found that associations between air pollution and lung function were two to five times stronger for obese children than for normal-weight children. The more obese a child was, the stronger the effect was of the previous day's air pollution on his or her lung function.

"Fatty tissue releases the pro-inflammatory substance interleukin 6 (IL-6), and increased levels of IL-6 and other markers of systemic inflammation (increased white blood cell counts, elevated c-reactive protein) have been found in the blood of obese children and adults," Dr. Gibson said. "Since air pollution also leads to inflammation of the airways, we think there is a multiplier effect that makes obese children more sensitive to air pollution."

Of the 611 children in the study, 10% were obese according to the study's definition.

Each child's lung function was measured, and compared with the level of air pollution during the previous day. The higher the air pollution on a given day, the lower the children's lung function was on the following day, with a greater effect seen in the obese children.

"Obesity in childhood causes a host of problems, including increased risk of diabetes, heart problems and asthma," Dr. Gibson said. "This study indicates that susceptibility to air pollution is one more harmful effect of childhood obesity."

The Harvard team is presenting another study at the American Thoracic Society meeting that shows that air pollution also has harmful long-term effects on obese children. That study, which followed children from fourth or fifth grade through 12th grade, found that long-term exposure to air pollution had irreversible effects on lung function in obese children.