Rain causes autism?
Bottomline: Probably not.
You may have read in the Seattle Post-Intelligencer today or heard on local television about a study that suggests children living in rainy counties in Washington have a higher risk of developing autism.
The stories spring from a paper published in the journal Archives of Pediatric & Adolescent Medicine this week.
In that paper, researchers compared autism rates in counties in Washington State, Oregon and California that have different amounts of precipitation.
They found that autism was more common in children living in counties that had high amounts of rainfall.
The lead author of the paper was Michael Waldman, an economist at Cornell University in Ithaca, New York.
The researchers speculate that there are many possible explanations why living where it rains a lot might increase a child’s risk of autism including:
- that rain may have keep children indoors, where, perhaps, they spend too much time watching television or playing computer games or where they are exposed to household chemicals that might trigger autism
- that rain, by forcing them indoors out of the sun, may have cause the children to have lower levels of vitamin D, which, in turn, affects their brain development.
- or that rain brings down harmful airborne chemicals that some how triggers the disease.
The problem with the study is that there are so many differences between the counties besides their rainfall rates.
In Washington, for example, the counties west of the Cascades have four-times the rainfall seen in the counties east of the mountains, but the rainy counties also are much more urban, have higher incomes, and children living there have access to different school programs and health services—all of which may lead to an increase in the diagnosis of autism but not a true increase in the actual number of cases.
Children in the western counties may be being over diagnosed, for example, while children in the eastern counties may be being under diagnosed, in which case, rainfall has nothing to do with it.
To their credit the authors of the study admit the many shortcomings of their study: “Because we do not provide direct clinical evidence of an environmental trigger for autism among genetically vulnerable children that is positively associated with precipitation, our results are clearly not definitive evidence in favor of the hypothesis,” they write.
But they argue the results are “consistent with” their hypothesis that there is a link between rainfall and autism rates warranting further research to establish “whether such a trigger exists….”
In an editorial accompanying paper, Noel Weiss, professor of epidemiology at the University of Washington, explains why he thinks the study “may well not lead to any insights into the etiologies of autism” but that the journal was still right to publish the paper even though nonprofessionals may “misinterpret and misuse it.”
Weiss notes, among other problems with the research, that “the criteria used to diagnose autism, and the completeness with which such diagnoses are identified by state agencies and regional centers, likely vary to a considerable extent across counties.”
Might not such differences exist between the rainy, relatively urbanized western counties of Washington and Oregon west of the Cascades and the arid, rural counties east of the mountains? he asks.
Nevertheless, despite concerns that the studies findings might cause undue worry among the general public, Weiss argues the paper’s publication was justified because the findings may help guideresearchers, who might, for example, now want to investigate the association between autism risk and vitamin D levels or exposure to indoor chemicals.
“The primary audience for the article of Waldman et al is not the practicing pediatrician, and certainly, it is not a member of the public at large,” Weiss writes. “These individuals cannot take away any practical message from it.”
To learn more:
- Read the original article in the journal Archives of Pediatric & Adolescent Medicine and Weiss’s editorial (fee or subscription may be required).
- Read the Seattle Post-Intelligencer article.
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