Autism and Air Pollution: The Link Grows Stronger

Studies continue to suggest that in utero exposure to pollution can raise the risk of autism

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Children with autism are two to three times more likely than other children to have been exposed to car exhaust, smog, and other air pollutants during their earliest days, according to a new study.

That new research adds to a mounting body of evidence that shows a link between early-life exposure to pollution and autism spectrum disorders.

MORE: Autism Rises: More Children Than Ever Have Autism, But Is the Increase Real?

For the new study, published in the Archives of General Psychiatry, researchers in California analyzed some 500 children living in that state: roughly half had autism and half did not. The kids’ mothers gave an address for each and every home in which they had lived during pregnancy and the child’s first year of life. Researchers took that information — along with data on traffic volume, vehicle emissions, wind patterns, and regional estimates of pollutants like particulate matter, nitrogen oxide, and ozone — to estimate each child’s likely pollution exposure. According to the study, children in the top 25% of pollution exposure (using one of two different pollution scales) were far more likely to be  diagnosed with autism than kids in the bottom 25% of the pollution scale.

The researchers stress, however, that their study does not definitively prove that pollution is the root cause of autism.

“We’re not saying that air pollution causes autism. We’re saying it may be a risk factor for autism,” says Heather Volk, lead author on the new study and an assistant professor of preventive medicine at the University of Southern California. “Autism is a complex disorder and it’s likely there are many factors contributing,” she says.

MORE: Researchers Discover Genetic Patterns of Autism

In particular, she says, genetic differences may leave some children more susceptible than others to the effects of damaging environmental stimuli such as air pollutants. Still, changes in air pollution over time cannot completely explain the entire disturbing rise in autism prevalence over the past two to three decades. According to the Centers for Disease Control and Prevention (CDC), 1 in 88 U.S. children has now been diagnosed with an autism spectrum disorder. And the pollutants that Volk and colleagues analyze are not necessarily more common today than they were 30 years ago.

Even so, the latest study findings suggest that air pollution may be one of the best characterized environmental risk factors for autism. In an earlier study published in 2010, Volk and colleagues showed that kids with autism were much more likely than kids without the disorder to have been born to mothers living within 1,000 feet of a freeway. Other researchers have shown that kids with autism are also unusually likely to have exposure to high levels of diesel exhaust particles and metals (mercury, cadmium, and nickel) and to other air-pollutant chemicals, such as those used to make rubber, plastics, and dyes.

MORE: Pollution in Utero

These associations continued to remain strong even after researchers adjusted for other characteristics, like poverty, that may also be connected to pollution. Unlike asthma, for example, autism rates are not consistently higher among lower income populations. In Volk’s study, the links between air pollution and autism risk were virtually unchanged after accounting  for parents’ race and ethnicity, educational attainment, and smoking status, as well as for the area’s population density.

The new study builds on previous research into the relationship between air pollution and autism with two  new insights. One is the focus on nitrogen dioxide (a common by-product from motor vehicle engines and power plants) and to particulate matter (dust, soot, and smoke in the air). The other is the study’s detailed, fine-grained data on individuals’ exposure to air pollution. For their research, Volk and her colleagues recorded information not just about proximity to major roadways, but also about whether homes were downwind or upwind from the roads, and the traffic load on these roads, in addition to regional-level data from the Environmental Protection Agency on other pollutant compounds. The researchers also looked at exposure throughout pregnancy and during the first year of life, and did not limit their measurements to a single point in time.

MORE: Hazardous Haze

Because conditions like autism are likely the result of a complex interaction between genetic and environmental factors, however, the new findings may ultimately raise as many questions as they answer. It’s not clear how or why the chemicals we breathe may affect development and autism risk, for example, although the researchers suggest that pollutants may impact both neurological development and inflammation, which can damage the lining of blood vessels in the brain and compromise the blood-brain barrier.

As research into the role that air pollutants can play in autism continues to grow, say the scientists, anti-pollution laws may be passed that could ultimately affect rates of the disorder.

22 comments
DarrylTouchet
DarrylTouchet

Further, I have to say something to these people blaming vaccinations.  YOU are the reason that measles is starting to creep up again.  Preventing your child from receiving vaccinations is just plain irresponsible.  You are putting your child and every child around them in mortal danger from dying from serious disease.  It has been shown that there is NO correlation between vaccinations and autism cases.

DarrylTouchet
DarrylTouchet

Well, if automobile exhaust is the issue, you can forget it.  The government will do nothing to help it.

Doublefrost
Doublefrost

Bull-feces. To say it 'politely'. It's genetic. I have no doubts that some forms of autism can be caused by environmental factors and brain damage but the way that all forms of autism are blindly and non-scientifically lumped together, oddly, as a deliberate act to consolidate a broader, more scientific attempt of classification into something politically expedient makes research very difficult to perform in a credible way.

Amy Kafuuma
Amy Kafuuma

@ chad revis mercury was taken out anout 10 15 years ago! and @ Carolyn....they have been studied. But if you are a concerned, split your vaccines up. If you still don't believe, travel to Africa...and see what vaccines do:) They save lives!

Carolyn Pierce
Carolyn Pierce

I'd like to know who funded this study. The government will do anything to keep their toxic vaccines out of the debate, which is why there never have been reliable studies on the efficacy & dangers of vaccines, yet they claim vaccines are safe.

James Carroll
James Carroll

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Chad Revis
Chad Revis

It's the vaccines! Read the ingredients and look them up! Mercury is a big no no!

in8health
in8health

So, as the article states, "kids with autism are also unusually likely to have exposure to high levels of diesel exhaust particles and metals (mercury, cadmium, and nickel) and to other air-pollutant chemicals, such as those used to make rubber, plastics, and dyes." Yet, shooting these metals and chemicals directly into the blood stream (vaccines) has no impact on these kids??  Really??

MariposaX
MariposaX

@kimzzz @time @timehealthland You'd still have to have a genetic predisposition; this is the mercury (non)argument all over again.

Denesius
Denesius

Many of the responders are on the money with their observation, and the truthis that autism is rampant in developed countries, even when you factor in thevariable for increased diagnosis. Furthermore, even in the age of improveddefinition and diagnosis, the incidence continues to rise even in the face offalling environmental pollution.The volume and passion of the responses to this article ignores thisfundamental fact: You can find causal relationships in just about anything, ifyou dig hard enough and your data base is small or inadvertently skewed.  Ibet anyone I can find a positive causal relationship between the number ofbreaths you take and your probability of demise, therefore concluding thatholding your breath as long as you can & as often as you can every dayshould help you live longer.

johnnyrenonv
johnnyrenonv

It boggles my mind that things like this are touched on like they'rre some sort of stunning new find, then people actually argue about it!  Yes, breathing burned fossil fuels, melting plastic, etc will harm you.  WTF?

SawabKing
SawabKing

@Innocentious Im talking about obvious mental retardation. The number of obvious mental retards I have seen in USA is 10X more than I ever saw in India in my 20 years there. Im not talking about "maybe" autistic cases or cases where parents want to brand their kid autistic to collect on welfare checks.

Innocentious
Innocentious

<sigh> first of all in urban areas you are far more likely to even go and get diagnosed as being Autistic. In first world countries versus third world countries this is also the case as well. My family is riddled with High Functioning Autistic's  Just try to tell me there is not a genetic predisposition. It has worked out fairly well for us though as these abilities while annoying as all get out leads to some fairly brilliant people who excel in whatever industry they choose to enter. Of course by that same token we have the social graces of a Bull in a China Shop...

gruffybear
gruffybear

As someone who has a brother with Autism and has followed the science for the last 40 years, I believe that the cause is almost certainly in utero. Studies of Thalidomide births has shown a high rate of autism when exposure that substance occurs during the 20th to 24th d of gestation. These findings, concerning brain stem development, may mean that whatever the cause, some factor, perhaps chemical, mechanical, or genetic is acting on fetal development at that early stage. I find it hard to believe that such profound physical changes occur after birth.

BN
BN

If this were true, far more children born in the 50's and 60's would have been autistic due to the high levels of smog in the cities--statistical data does not support this. In California, Pasadena alone was a haze of smog as particulates packed into areas near the hills of LA and it was common for your chest to hurt after being out on very smoggy days.  Currently, there would be a high autism rate in the high smog cities in China and other countries that have not put through emissions laws--is this true?  Do other countries with high smog have high autism rates? This is not to say that smog is not unhealthy, I just don't see where the premise holds up looking at the findings historically and in current world cities.  I did not note in the article who funded the study.  

SawabKing
SawabKing

Thats just baloney. 3rd world countries have the highest amount of pollution but probably have the lowest incidents of autism.

DarrylTouchet
DarrylTouchet

@Doublefrost No one said it wasn't genetic.  But genetics alone can't account for the increases seen in the number of cases lately.

DarrylTouchet
DarrylTouchet

wrong again.  They have already done a study on that and found that this is not the case.  There is no correlation between vaccines and autism.  

BlandonGranger
BlandonGranger

@BN remember gasoline mixtures are much different today than they were back then with more additives and they also very regionally. More research is needed to make a final conclusion.

SawabKing
SawabKing

but then again, you DO see a lot of people in third world countries with small pox marks and polio after-effects. Oh yeah, maybe they dont use vaccines as often?!