Could the weather forecast predict rates of autism? According to a paper from Michael Waldman of Cornell University, children living in areas with higher levels of precipitation have higher rates of autism than those living in low rainfall areas.
“There seems to be a strong association between precipitation and autism diagnosis rates,” says Waldman (Washington Post). “Our finding strongly suggests that there is some factor which is positively correlated with precipitation, which is serving as a trigger for autism.”
Waldman and colleagues looked at precipitation rates in counties in California, Oregon and Washington between 1987 and 2001. They compared this with the autism prevalence rates for school children in those states and found a positive correlation, they report in Archives of Pediatrics & Adolescent Medicine.
The researchers posit a number of possible explanations:
1. Rain leads to children staying indoors more and watching television: “So one possibility is that early childhood television and video viewing by typical children is associated with various mild negative health consequences, whereas in a genetically vulnerable population it is associated with more serious health problems such as autism.”
2. Vitamin D deficiency leads to autism, and rain leads to people staying indoors more.
3. “Any environmental trigger associated with indoor activities”, a chemical in household cleaners for example, could be the cause.
4. “Finally, there is also the possibility that precipitation itself is more directly involved.” This could be by transporting chemicals down from the atmosphere.
Not everyone is convinced, with some backing a fifty explanation: the correlation is an artefact.
In an editorial accompanying the paper Noel Weiss, of the University of Washington, Seattle, writes:
They have made it clear that the message the public should take from their data regarding precipitation and autism is the same one suggested by an editorialist commenting on a recently observed modest association between prenatal exposure to cell phone use and behavior problems in childhood: “No call for alarm, stay tuned.”
Uta Frith, of the UCL Institute of Cognitive Neuroscience in London, is even more sceptical. In comments distributed by the Science Media Centre Frith says, “This study shows the danger of simply collecting prevalence data without a specific hypothesis. Sadly, the correlations found cannot be interpreted. It is likely that this result will vanish just like correlations found previously with season of birth, position in sibling order, parental age and vaccines.”