Experts emphasize that the exact causes of autism remain unknown, and some say that the researchers in this study did not analyze every potential risk factor.
However, the study “adds to the growing concern that there can be no safe levels of exposure to air pollution,” Pagalan wrote in an e-mail.
“Not only did we gain access to rich data, which allowed us to develop one of the largest studies to date, but we were also able to conduct this research in a city with a relatively lower level of air pollution,” he said.
More than 100,000 children studied
Pagalan and his colleagues analyzed the records of 129,436 children born in Vancouver from 2004 to 2009.
“We analyzed data on air pollution in Vancouver over the same period to assess the impact of air pollution on a pregnant woman,” he said. "Their children were monitored for at least 5 years to find out if they were diagnosed with autism spectrum disorders."
Overall, about 1% of children were diagnosed with autism at the age of 5, the researchers found. They compared the rates of autism among children of women who were exposed to the least amount of air pollution during pregnancy compared to those among children of women who were most affected.
All three measurements of air pollution (particulate matter, nitrogen dioxide and nitrous oxide) showed a similar relationship with autism.
The chances of developing autism among children prenatally subjected to elevated levels of PM2.5 (particle size less than 2.5 micrometers in diameter) were 1.04%, the probability of autism in children exposed to higher levels of nitrogen dioxide was 1.06%, The chances of autism in children exposed to higher levels of nitric oxide were 1.07%. This final increased risk turned out to be “statistically significant”, which means that he crossed the line from random odds and shows true relationships.
Pagalan said that the causes of autism are not fully known. “They are complex and have many factors, but researchers recognize that genetics and environmental factors play a role,” he said.
Experts say that any link between air pollution and autism is small at best.
Autism takes place in families, and its causes remain unknown
However, in her opinion, the authors “beautifully addressed” some flaws in previous studies of the same subject. For example, criteria for children with autism included only those who received the “gold standard” diagnosis based on data from the autism assessment network in British Columbia.
However, other important factors were not included in the analysis, she said, for example, socio-economic status, which, as has been shown, is associated with autism.
“In addition, the focus was on the language environment of mothers, and it is possible that the workplaces of mothers have different ecological composition that may be important to consider,” she wrote in an e-mail. “Perhaps these pollutants and / or other influences affect fathers and their sperm quality.”
“Autism is highly genetic, we know this because it works in families,” said Cusack, who did not participate in the study. He added that the researchers found only a “slight increase” in the likelihood of having an autistic child for women exposed to more air pollution, in particular nitric oxide. “Other differences that have not been measured, such as genetic differences, may explain this increase. This study does not provide evidence that air pollution causes autism. ”
“In a broad sense, the results of the study were the same for all three pollutants,” said McConway, who did not participate in the new studies. However, only nitric oxide went to the "traditional margin of statistical significance," he said, "and only slightly higher."
“In such studies, it’s really impossible to truly understand the reasons for what,” he said. “Perhaps air pollution does affect [autism] risk, or perhaps not. " Although the study "adds more evidence," he concluded, "we are very far from knowledge."
Pagalan said that because of the lack of treatment for autism, “identifying risk factors for the environment helps identify opportunities for prevention.”