Pollution Link to SIDS Is Probed

New government research shows that tiny particles of air pollution may contribute to sudden infant death syndrome--a finding that an environmental group said Thursday points toward dirty air as an explanation for 45 infant deaths in parts of Southern California.

For several years, scientists have known that more adults die from cardiac and respiratory ailments on days when particulates--microscopic pieces of carbon soot, sulfur and other pollutants--increase.

But the new study, conducted by federal government researchers and published last week in a National Institutes of Health journal, is the first to find that the rate of infant mortality also seems to increase as particle pollution rises.

The study found that babies in highly polluted areas were 26% more likely to die of SIDS than those who live in cities with cleaner air.

Extrapolating from that data, two advocacy groups, the Environmental Working Group and Physicians for Social Responsibility, estimated Thursday that particulates could be responsible for 500 cases of SIDS nationwide each year, including 45 in Los Angeles, Orange and Riverside counties.

The estimated number of deaths in Southern California was the highest in the country, reflecting the fact that the Los Angeles Basin, especially around Riverside, has the nation’s highest concentrations of particulates, largely due to emissions from cars and trucks.

Medical experts do not know how or why particles seem to increase deaths among people with respiratory or heart diseases--some suspect that the particles may irritate nerves that control the heart.

The report is certain to add to a major controversy over the health effects of particulate pollution. That controversy is at the center of the debate over controversial standards the Clinton administration is about to adopt that would limit the amount of ultra-fine particles allowable in the air. Under those tougher standards, about 167 counties nationwide, including most of Southern California, would have air deemed unhealthful and would face potentially costly new cleanup bills.

The new study has several limitations. Most important, the study, which reviewed health records of nearly 4 million babies born in the United States between 1989 and 1991, excluded babies in California and New York because those states do not track critical data concerning smoking by the parents--a known risk factor for SIDS.

Ronald Harper, a UCLA neurophysiologist who specializes in SIDS, said the study could be pinpointing a previously undisclosed factor in the unexplained sudden deaths of babies while they sleep. But Harper and other experts remain skeptical because of the limitations of such studies that try to track environmental influences on disease.

“This is an important first study but it is a mistake to say air pollution causes SIDS because the mechanisms involved are far more involved than just air pollution,” Harper said. “These authors have pointed out an important environmental stressor, and this stressor along with important other issues, such as prenatal factors, may contribute to SIDS.”

More than 3,800 infants in the United States died of SIDS in 1994. Doctors suspect that the babies’ heart and respiratory rates slow and their blood pressure drops as they sleep.

The federal scientists, led by U.S. Environmental Protection Agency epidemiologist Tracey Woodruff, discovered that in cities with low particulate pollution, 1 of every 1,000 babies died of SIDS, compared with 1.13 in cities with medium pollution and 1.26 in highly polluted cities, according to the article published in Environmental Health Perspectives.

*

The researchers found that babies in the highly polluted cities were 10% more likely to die of SIDS even when differences in birth weight, race, smoking by the mother during pregnancy and temperature--all factors that contribute to SIDS--were factored out. The study did not attempt to distinguish between babies who slept on their stomachs and those who slept in other positions.

Some experts question how infants who spend most of their time indoors could be injured by outdoor pollution. California researchers, however, have found high particulate levels indoors.

But Harper noted that other factors, such as income of the families, could play a role in the higher death rates found in the polluted cities. “It could be due to some other factor in the people who live in these cities,” he said.

While the environment after birth can be an important contributor to SIDS, the infant deaths often are related to what happens while the baby is in the womb--such as cigarette smoking by the mother or abnormal cardiovascular development, Harper said.

Deaths from SIDS have declined 30% over the past few years because doctors now tell parents that infants should not sleep on their stomachs or on soft bedding. Babies also are at higher risk of SIDS if exposed to secondhand smoke or if their mothers smoked while pregnant.

The Environmental Working Group used the risk rate from the study to extrapolate the city-by-city number of annual SIDS deaths that might be tied to pollution. Because of its severe pollution and large population, the Los Angeles-Orange-Riverside counties area ranked first with 45, followed by the New York City metropolitan area with 29 and the Chicago area with 27.