Pregnant women who live in areas with high levels of air pollution caused by heavy traffic could be at increased risk for premature births, according to a new study.
Researchers led by Michelle Wilhelm, an assistant professor in residence at the UCLA School of Public Health, found that Southern California women exposed to traffic-related air pollution had a 30 percent higher risk of pre-term birth.
Wilhelm and her colleagues looked at 100,000 births that occurred in Los Angeles County within five miles of stations used by the state to monitor air quality.
Using birth records and specific exposure information provided by the state, they determined that polycyclic aromatic hydrocarbons (PAHs), chemicals found in soot, were associated with the highest risk of premature births. They found that traffic was the biggest source of PAHs.
"Even at air pollution levels in Los Angeles which are much lower than in previous decades, we still see adverse birth outcomes that we attribute to traffic-related air toxics," said Dr. Beate Ritz, a co-author and professor of epidemiology at the UCLA School of Public Health.
"This research fits with a whole body of literature over the past decade that show problems between a woman's exposure to pollution and pregnancy and subsequent health of the baby," said Dr. Philip Landrigan, director of the Children's Environmental Health Center at the Mount Sinai School of Medicine in New York. Landrigan was not involved in the California research.
The study also found that other chemicals, such as ammonium nitrate and benzene, were also associated with an increased risk of premature birth, but to a lesser extent.
Babies and children exposed to certain pollutants are known to be more susceptible to health problems.
"It's known that when pollutants get into pregnant women and their baby, they disrupt the metabolism of the baby," said Landrigan. "Infants exposed to air pollution are at higher risk for asthma, respiratory infections and sudden infant death syndrome (SIDS)."
The authors said other factors could be contributing to the risk of premature births in these women. The women living in the affected areas were more likely to be Hispanic, born outside the U.S., lower-income and have government health insurance. Because they used birth data, the researchers were unable to control for the effects of smoking as well.
"The findings are complex because most of the populations at risk are populations with historic health disparities," said Dr. Maureen Lichtveld, chair of environmental policy at the Tulane University School of Public Health and Tropical Medicine in New Orleans. They may not have easy access to health care, or may live in areas where pollution is rampant.
She also said that while these findings are very important, limitations on funding make it impossible to study the full effects of air pollution in the best way possible.
"If we were able to do this right, we would actually directly measure air pollution outdoors, indoors and on the people themselves. The contributions of indoor and personal exposure are in many cases greater than outdoor exposure," she said.
She explained, for example, that personal exposure is increased by putting gas in a car. In that case, the amount of benzene is increased. Smoking is also another source of personal exposure.
Perhaps the best ways to limit exposure to traffic-related air pollution, experts said, are to move out of the areas and to keep off the roads, but those are not always feasible options.
Not smoking and eating a lot of fruits and vegetables with that can help the body fight off toxins are other options, but Ritz added that environmental regulations must also change.
"We clearly need to reconsider transportation policies to reduce exposures to large populations in dense metropolitan areas," she said.