An epidemiological study published recently in the Archives of Pediatric and Adolescent Medicine found that counties in the United States with high levels of precipitation have higher rates of autism than counties with low levels.
“If there were no rain, the autism rate would be a third lower according to our analysis,” says study author Sean Nicholson ( WebMD , 3 November 2008). Nicholson speculates that “It could be the rain itself...” (WebMD), whereas Michael Waldman, another author on the paper, says: “...my guess is it is one of the factors related to indoor activity.” (WebMD.)
Rainfall joins a long list of factors that have been associated with autism, including “older aged fathers, early television viewing, vaccines, food allergies, heavy metal poisoning, and wireless technology,” says Mark Lever, chief executive of the National Autistic Society ( Telegraph , 3 November 2008). But it is difficult to establish a causal role for such factors, and in many cases, notably that of vaccines, the link has subsequently been discredited.
So, is the association between autism and rainfall real? “It could be, but I don't think so ... it's probably worth looking into,” says Noel S. Weiss, a professor of epidemiology at the University of Washington in Seattle ( Washington Post , 3 November 2008).
But not everyone is convinced of the validity of the study. To Lee Grossman of the Autism Society of America, “It just does not seem plausible.” According to Grossman, “It does not match up with any of the demographics that we follow.” ( USA Today , 4 November 2008.) Michael Fitzpatrick, a London GP, puts it somewhat stronger: “The notion that autism is caused by higher rainfall is manifestly absurd.” ( BBC News , 4 November 2008.)
For now, there are probably better reasons to move to a sunny climate than to prevent autism.
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Welberg, L. Rain man?. Nat Rev Neurosci 9, 888 (2008). https://doi.org/10.1038/nrn2553