Rainy Areas in U.S. Show Higher Autism Rates
Monday, November 3, 2008; 12:00 AM
MONDAY, Nov. 3 (HealthDay News) -- Children who live in areas of the United States that get a lot of precipitation appear to have a higher risk of developing autism, a new study suggests.
Because these children may spend more time indoors or because rain brings chemicals in the atmosphere to the ground, they might be exposed to environmental triggers that can trigger a genetic predisposition to autism, the researchers say.
"There seems to be a strong association between precipitation and autism diagnosis rates," said lead researcher Michael Waldman, a professor of economics at the Johnson Graduate School of Management at Cornell University.
Waldman, whose son was diagnosed with autism spectrum disorder, isn't saying that rain causes the condition. "Our finding strongly suggests that there is some factor which is positively correlated with precipitation, which is serving as a trigger for autism," he said.
One possible explanation for this correlation is vitamin D deficiency, Waldman said. "There is a fair amount of research that vitamin D deficiency in young children causes problems. As children aren't outside as much, they aren't getting enough vitamin D, and that's serving as a trigger for autism," he said.
Another possibility is children are spending too much time watching TV or videos, Waldman said. "There are various papers showing associations between early childhood television viewing and various problems concerning cognitive outcomes, sleep problems, behavior problems, etc.," he noted.
A third possibility is exposure to chemicals in the home which trigger autism, Waldman said. In addition, there may be a chemical or chemicals in the upper atmosphere that are transported to the surface by precipitation.
There is debate about whether autism is caused by genetics alone or genetics and the environment, Waldman said. "Our results are inconsistent with it being just genetic."
The report was published in the November issue of theArchives of Pediatrics & Adolescent Medicine.
For the study, Waldman's team looked at the prevalence of autism among children in California, Oregon and Washington. They also used data from the National Climatic Data Center to calculate the average annual rainfall by county in these states.
The researchers found among school-aged children in these states that the prevalence of autism rose as the amount of precipitation increased. In fact, the prevalence in autism increased up to 30 percent in the rainiest counties.
Over the past three decades, the number of children diagnosed with any form of autism has increased from one in 2,500 children to one in 150 children. Some of the increase is most likely due to better diagnosis and the changing definition of autism, which now encompasses a variety of conditions called autism spectrum disorder.