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Study links autism to air pollution exposure in pregnancy

Women who are exposed to high levels of air pollution during their third trimester of pregnancy may be twice as likely to have an autistic child, a study found.

Standard Examiner, Dec 18, 2014

Researchers from the Harvard School of Public Health found the risk of autism rises in parallel with exposure to fine particulate matter during pregnancy, with the biggest effect occurring in the final months of gestation. The results appeared in Thursday’s edition of Environmental Health Perspectives.

The findings add to other research suggesting the environment plays a role in the development of autism, a developmental disorder marked by repetitive behaviors and trouble communicating and socializing. The study, which started in 1989 and involved more than 100,000 nurses from across the U.S., will help researchers home in on the causes of autism and potential ways to prevent it, said Marc Weisskopf, a senior study author.

“One of the unique aspects of the study we did is that it provides an even stronger piece of evidence for there being a causal effect,” said Weisskopf, an associate professor of environmental and occupational epidemiology at Harvard in Boston. “It’s really the pollution doing it.”

Autism, thought to affect 1 in 68 children in the U.S., is typically diagnosed after behavioral changes start to develop before the age of 5. Recent studies suggest it may begin when certain brain cells fail to properly mature within the womb.

Researchers focused on 1,767 children born from 1990 to 2002, including 245 diagnosed with autism. The design of the study and the results rule out many confounding measures that can create a bias, Weisskopf said. The researchers took into account socioeconomic factors that can influence exposure to pollution or play a role in whether a child is diagnosed with autism.

The fact that pollution caused problems only during pregnancy strengthened the findings, since it’s unlikely other factors would have changed markedly before or after those nine months, he said in a telephone interview.

Embracing the research in Utah

Jon Owen, president of the Utah Autism Coalition, praised the Harvard study and said it jives with the results of other research he’s seen. This analysis of pollution’s effects has the largest scale of anything he’s seen connecting air quality to autism, he said. 

“It’s definitely a very interesting data set they used. It seems like a high quality study,” Owen said. “It's not the first time we've heard about pollution causing autism. ... It's not a huge surprise to me.”

Expectant women can use this study and others like it as a happy excuse, Owen quipped, to avoid areas with exorbitant pollution levels. 

Dr. Brian Moench, founder and president of Utah Physicians for a Healthy Environment, said the study is part of a growing chorus about the silent effect of air pollution and other environmental factors on early brain development.

“This should be a wake-up call to lawmakers that we need to do something,” Moench said. “It’s one of many compelling reasons to take the task of cleaning up our air more seriously.”

One in 54 Utah children have autism, compared to 1 in 68 nationally, the Centers for Disease Control estimates. One in 34 boys in Utah has the condition, the CDC has said.

The high rate of autism in Utah is alarming, Moench said. Although air pollution is one of many autism’s possible contributing factors, he added, it ought to be taken seriously.

“That should compel this community to take this study even more seriously than even other cities or states.”

Autism is one of several medical conditions linked in some way to air pollutants and other toxic chemicals, Moench said. Multiple sclerosis, Alzheimer’s disease, early onset dementia and increased risk for stroke are all backed by research as having at least some correlation to environmental exposure. 

Polluted surroundings can also negatively affect brain development in some instances during early childhood and not just during an expectant mother’s pregnanc, according Moench.

“We need to look at this more comprehensively,” he said.

Moench recommends several precautions that “a pregnant woman can reasonably take.” These include:

UPHE will be hosting two related seminars early next year at the Salt Lake City library. The first will be held Jan. 29 at 7 p.m. and will address air pollution and its effects on brain development. The second, held Feb. 15, will discuss air pollution as it relates to pregnancy. Both will run for 1 hour, 15 minutes.

Environmental and genetic factors not mutually exclusive

The ultimate cause of autism remains a mystery in most cases, said Charis Eng, chairwoman of the Lerner Research Institute’s Genomic Medicine Institute at the Cleveland Clinic in Ohio. While the Harvard study isn’t definitive and the findings could be coincidental, it’s not likely given the large size and the precise results, she said in a telephone interview.

“The truth is there has to be gene and environmental interactions,” said Eng, who wasn’t involved in the study. “I suspect the fetus already had the weak autism spectrum disorder genes, and then the genes and the environment interacted.”

If the child didn’t have the genetic predisposition, the impact may have been minimal or nonexistent, she said.

It’s likely there is an inflammatory or immune system response to the pollution that reaches the fetus, Weisskopf said. His team is now exploring those biological pathways and mapping autism cases to see if there are any clusters. He emphasized that many things contribute to the disorder and the absolute risk from pollution may be very small.

Fine particulate matter stems from many different sources, including traffic and power plants located hundreds of miles away. There is no way to avoid it entirely, though pregnant women may want to try to curtail their exposure when possible, Weisskopf said. He recommended against trips to cities with high levels of pollution and exercise in traffic-clogged areas during pregnancy.

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