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Study Finds Higher Child Autism Rates In Rainy Climates

November 4, 2008

A Cornell University study has found a potential link between increased rainfall and the development of autism in children.  

The researchers used child health and weather records from three northwestern states, and found that rates of autism were higher among children living in the counties with the greatest amount of rainfall.

However, the reasons behind the potential link are not yet clear.

No one knows precisely what causes autism, a condition with symptoms ranging from severe social avoidance to repetitive behaviors and extreme mental retardation. Michael Waldman of Cornell University and his colleagues were initially investigating a possible environmental link with the autism.

The scientists obtained autism rates from state and county agencies for children born in Washington, California and Oregon between 1987 and 1999 and then plotted them against daily rainfall reports.

“Autism prevalence rates for school-aged children in California, Oregon and Washington in 2005 were positively related to the amount of precipitation these counties received from 1987 through 2001,” wrote the scientists in a report about the study.

However, the study has been given an chilly reception by Dr. Michael Fitzpatrick, a British physician and author of “Defeating Autism: A Damaging Delusion”,  who expressed doubt about the study, noting that autism rates are increasing in all climates.

The U.S. Centers for Disease Control and Prevention (CDC) estimates that roughly one in every 150 children has autism or a related disorder such as Asperger’s Syndrome.  Rates of autism are on the rise in many countries, although that could be partially attributable to an increase in reporting and diagnosis of the condition.  

Experts generally agree there is both a genetic and environmental component to autism, a theory the Cornell researchers say their study reinforces.

For example, infants and toddlers may be kept indoors in front of the TV more in rainy climates, and that may somehow cause changes in the brain changes, or perhaps more harmful chemicals are inhaled indoors, the researchers said. Additionally, vitamin D deficiency due to insufficient time in the sun might also be a factor, they said.

“Finally, there is also the possibility that precipitation itself is more directly involved,” they wrote in their report, adding that chemicals in the upper atmosphere are carried to the surface through rain or snow.

But the scientists emphasize these are all only theories, and say further researcher on the causes of autism is needed.

Mark Lever, chief executive of The National Autistic Society, said the rainfall theory joins a host of other ideas about the condition and its origins.

“In recent years autism has been linked to factors as varied as older aged fathers, early television viewing, vaccines, food allergies, heavy metal poisoning, and wireless technology, to name just a few,” he told BBC News.

“Some of these theories are little more than conjecture or have been discredited, others seem more promising and are in need of further study. As yet, however, very few have been substantiated by scientific research.”

“We don’t yet understand what causes autism, although scientists do believe that genetic factors might play a part.

“People with autism and their families are naturally concerned to get the right information and there is a lot of confusion and concern over the conflicting theories put forward.”

“In recent years autism has been blamed on everything from discarded iPod batteries to mercury from Chinese power stations, from antenatal ultrasound scans to post-natal cord clamping, from diet to vaccines,” said Fitzpatrick in a statement.

The CDC has started a long-term study to determine the causes of autism and other childhood conditions.

The Cornell study was published in the Archives of Pediatrics & Adolescent Medicine.

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