Washington, Nov 4 : Children who live in areas with higher annual rainfall levels could be more likely to develop autism - a brain development disorder that is characterized by impaired social interaction and restricted behavior - claims a new study.
The results raise the possibility that an environmental trigger for autism may be associated with precipitation and may affect genetically vulnerable children.
According to the study, in the past thirty years autism rates have increased from one in 2500 children to one in 150, and the higher rate of precipitation affecting genetically vulnerable children can be held responsible for the growing rate.
The authors behind the study say that precipitation may be allied with disorder, as more indoor activities, such as television and video viewing, affect behavioral and cognitive development.
The greater amount of time spent indoors may also expose children to more harmful chemicals, such as those in cleaning products, or decrease their exposure to sunshine, which helps the body produce vitamin D, which is vital for proper growth.
"Finally, there is also the possibility that precipitation itself is more directly involved. For example, there may be a chemical or chemicals in the upper atmosphere that are transported to the surface by precipitation," the author said.
Michael Waldman, Ph.D., of Cornell University, Ithaca, N.Y., and colleagues obtained autism prevalence rates from state and county agencies for children born in California, Oregon and Washington between 1987 and 1999. The daily precipitation reports from the National Climatic Data Center, they calculated average annual rainfall by county from 1987 through 2001-which spans the dates when the children were school-aged.
The calculation indicated that 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.
"Similarly, focusing on Oregon and California counties with a regional center, autism prevalence was higher for birth cohorts that experienced relatively heavy precipitation when they were younger than 3 years. This corresponds to the time at which autism symptoms usually appear and when any post-natal environmental factors would be present," the author said.
Thus the study indicated that precipitation or its consequences like increased television watching, reduced vitamin D levels and enhanced exposure to indoor chemicals might increase the rate of autism.
The study has been published in the November issue of Archives of Pediatrics and Adolescent Medicine, one of the JAMA/Archives journals.