On Ramp to Autism: Do Freeways Trigger Autism?

Pregnant women living near freeways were almost twice as likely to have a child later diagnosed with autism, the neurodevelopmental disorder characterized by deficits in social interaction and communication.

The freeway hypothesis sounds reasonable: Pollution bad and fetuses fragile, alas, autism.

What better place to test it than California, land of abundant freeways, environmental awareness and celebrity autism activist Jenny McCarthy. Our freeway study comes from a larger project on the origins of autism, CHARGE -- The Childhood Autism Risks from Genetics and the Environment Study. The researchers pulled data out for over 500 preschoolers around Los Angeles, Sacramento and San Francisco. Then they calculated how far the mothers lived from a freeway or major roadway at each trimester in pregnancy. The children whose mothers lived the closest to the freeways during the third trimester were 86 percent more likely to be diagnosed with autism.

Sounds alarming.

But notice third trimester. It wasn't any riskier near highways in utero during the beginning or middle of pregnancy. I bet the researchers checked several other time periods (e.g., before pregnancy, after birth, each month thereafter). This report only includes the trimesters so I suspect the others didn't pan out. Nobody holds back significant results that bolster their case.

Now look at closest. These kids were gestated less than one-fifth of a mile from freeways. They were more at risk than those almost a mile away. But here's the weird part. Living near a heavily-traveled road, which might include a freeway, didn't raise the risk. How close? Within 46 yards. That's less than the width of a football field, from say produce to poultry at the supermarket. Apparently sleeping on the shoulder of a major roadway is not any riskier. Freeway pollution from a further distance seems more harmful than major road pollution practically in your bedroom. Doesn't make a lot of sense.
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Maybe it's simply a matter of traffic volume and thus freeways producing more traffic and air pollution.

Air pollution.

Study didn't measure it. Not around freeways, neighborhoods or wombs. Nor the level of traffic, noise or population density. What do we often find next to interstates around urban areas? Apartment buildings, condos, and housing developments. That's plenty of people per square mile. If lots of folks live near highways we can't be surprised to find more kids with autism too.

We need to know more about the origins of autism, but, I'm always wary when data get pulled from larger studies. A wealth of numbers and such means it's easier to find significant results. With each analysis there's an increased chance of a false positive, in other words, a freak significant result. It's an epidemiological grab-bag, a fishing expedition. Oh look, we got one!

I'm also suspicious because there's only one significant result. Throw in the lack of higher risks nearer the major roads, the missing estimates for air pollution and population density and I'm not convinced this research is on the right path, road or route. It's messier than the 101 at rush-hour.

My advice? Don't start packing yet if you live just off the interstate.