Small particles from traffic and heating oil combustion may cause children younger than two to wheeze and cough, according to a new study.

High air pollution levels have previously been linked to asthma symptoms in children living in urban areas with heavy traffic, but this study is one of the first to investigate the types of particles that may be the most harmful, the researchers point out in the American Journal of Respiratory and Critical Care Medicine.

This study shows that there are multiple components of air pollution that we should be looking at in terms of health effects, Dr. Rachel L. Miller, lead investigator of the study, said in a telephone interview with Reuters Health.

Miller, co-deputy director of the Columbia University Center for Children's Environmental Health in New York City, and her team followed more than 700 children from birth to age two. All of the children lived in northern Manhattan or the south Bronx. Every three months, parents filled out a questionnaire about any respiratory symptoms the infants had experienced. The study took into account factors such as seasonal allergy trends, ethnic group and exposure to tobacco smoke.

After comparing the results of the questionnaires with weekly pollution data from different sites in the community, the researchers found that high ambient levels of the metals nickel and vanadium were risk factors for wheezing, while exposure to carbon particles, a byproduct of diesel exhaust, was associated with coughing during the cold and flu season.

Total amounts of airborne particles were not associated with wheeze or cough, suggesting that individual ingredients of air pollution may be responsible for asthma symptoms in young children.

The EPA currently sets air pollution standards based on total mass of fine particles.

This new study raises questions about the best way to regulate air pollution to protect young children from its harmful effects, Dr. Frank Gilliland, director of the Southern California Environmental Health Sciences Center, who was not involved in the study, told Reuters Health.

According to Miller, This study adds to a growing body of research suggesting that exposure to pollutants early in life may have health impacts later on.

SOURCE: American Journal of Respiratory and Critical Care Medicine, December 1, 2009.