Prevalence of Autism in Three States Linked to Precipitation

Autism prevalence in three Western states has been linked to precipitation there, so that the heavier the precipitation, the higher the prevalence of the disorder among genetically vulnerable children, a report in the Archives of Pediatric and Adolescent Medicine shows.

This finding supports the hypothesis that an environmental trigger may play a significant role in autism, affecting children who are already genetically predisposed to the disorder.

“Our results clearly are not definitive … but [they] are consistent with the hypothesis, and, therefore, further research focused on establishing whether such a trigger exists and on identifying it is warranted,” said Michael Waldman, Ph.D., of the Johnson Graduate School of Management, Cornell University, Ithaca, N.Y., and his associates.

The investigators noted that several state surveys overseen by the U.S. Department of Education and a recent Centers for Disease Control and Prevention study all indicated that autism prevalence is higher in certain northern regions of the country, and lower in dry areas of the south and southwest.

They assessed a possible correlation with precipitation in Washington, Oregon, and California, where regions west of the mountains receive almost four times as much precipitation as do regions to the east. Using regression analysis, the investigators found that autism prevalence was higher in counties that received abundant precipitation. It also was higher for birth cohorts that received above-average precipitation relative to the usual amount in that county, Dr. Waldman and his associates said.

“The magnitude of the measured relationships is substantial,” they noted (Arch. Pediatr. Adolesc. Med. 2008;162:1026-34).

They are not proposing that autism is related to rain and snow per se, but that it may be related to indoor activities or exposures that are increased during bad weather.

For example, early, excessive television and video viewing has been associated with psychopathological traits such as poor language and cognitive development. It may be that this exposure produces only mild health consequences in most children but produces more serious problems such as autism in genetically vulnerable children.

“Another possibility is that vitamin D deficiency is an environmental trigger for autism,” the researchers wrote. Higher precipitation means less exposure to sunshine, the major source of vitamin D, and vitamin D deficiency “can lead to reduced levels in the developing brain of calcitriol, a critical neurosteroid involved in brain development,” they added.

Any environmental trigger that is associated with indoor activities could be at fault, including household chemicals. And it also is possible that precipitation is more directly involved, by transporting chemicals in the upper atmosphere to the ground, for example. Or high precipitation may promote the overgrowth of weeds or expansion of the insect population, which in turn increase the use of pesticides, they wrote.

In an accompanying editorial, Dr. Noel S. Weiss of the University of Washington, Seattle, noted that the study findings are “tentative” and were intended to prompt further research into environmental triggers, not to implicate rainfall itself.

“The primary audience of Waldman et al is not the practicing pediatrician, and certainly, it is not a member of the public at large. These individuals cannot take away any practical message from it. Rather, the primary target is an investigator interested in the causes of autism, someone who might be able to test one or more of the etiologic hypotheses that derive from [the study],” he said (Arch. Pediatr. Adolesc. Med. 2008:162;1095-6).

The researchers “have made it clear that the message the public should take from their data regarding precipitation and autism is … 'No call for alarm, stay tuned,'” Dr. Weiss wrote.

Autism prevalence in three Western states has been linked to precipitation there, so that the heavier the precipitation, the higher the prevalence of the disorder among genetically vulnerable children, a report in the Archives of Pediatric and Adolescent Medicine shows.

This finding supports the hypothesis that an environmental trigger may play a significant role in autism, affecting children who are already genetically predisposed to the disorder.

“Our results clearly are not definitive … but [they] are consistent with the hypothesis, and, therefore, further research focused on establishing whether such a trigger exists and on identifying it is warranted,” said Michael Waldman, Ph.D., of the Johnson Graduate School of Management, Cornell University, Ithaca, N.Y., and his associates.

The investigators noted that several state surveys overseen by the U.S. Department of Education and a recent Centers for Disease Control and Prevention study all indicated that autism prevalence is higher in certain northern regions of the country, and lower in dry areas of the south and southwest.

They assessed a possible correlation with precipitation in Washington, Oregon, and California, where regions west of the mountains receive almost four times as much precipitation as do regions to the east. Using regression analysis, the investigators found that autism prevalence was higher in counties that received abundant precipitation. It also was higher for birth cohorts that received above-average precipitation relative to the usual amount in that county, Dr. Waldman and his associates said.

“The magnitude of the measured relationships is substantial,” they noted (Arch. Pediatr. Adolesc. Med. 2008;162:1026-34).

They are not proposing that autism is related to rain and snow per se, but that it may be related to indoor activities or exposures that are increased during bad weather.

For example, early, excessive television and video viewing has been associated with psychopathological traits such as poor language and cognitive development. It may be that this exposure produces only mild health consequences in most children but produces more serious problems such as autism in genetically vulnerable children.

“Another possibility is that vitamin D deficiency is an environmental trigger for autism,” the researchers wrote. Higher precipitation means less exposure to sunshine, the major source of vitamin D, and vitamin D deficiency “can lead to reduced levels in the developing brain of calcitriol, a critical neurosteroid involved in brain development,” they added.

Any environmental trigger that is associated with indoor activities could be at fault, including household chemicals. And it also is possible that precipitation is more directly involved, by transporting chemicals in the upper atmosphere to the ground, for example. Or high precipitation may promote the overgrowth of weeds or expansion of the insect population, which in turn increase the use of pesticides, they wrote.

In an accompanying editorial, Dr. Noel S. Weiss of the University of Washington, Seattle, noted that the study findings are “tentative” and were intended to prompt further research into environmental triggers, not to implicate rainfall itself.

“The primary audience of Waldman et al is not the practicing pediatrician, and certainly, it is not a member of the public at large. These individuals cannot take away any practical message from it. Rather, the primary target is an investigator interested in the causes of autism, someone who might be able to test one or more of the etiologic hypotheses that derive from [the study],” he said (Arch. Pediatr. Adolesc. Med. 2008:162;1095-6).

The researchers “have made it clear that the message the public should take from their data regarding precipitation and autism is … 'No call for alarm, stay tuned,'” Dr. Weiss wrote.

Autism prevalence in three Western states has been linked to precipitation there, so that the heavier the precipitation, the higher the prevalence of the disorder among genetically vulnerable children, a report in the Archives of Pediatric and Adolescent Medicine shows.

This finding supports the hypothesis that an environmental trigger may play a significant role in autism, affecting children who are already genetically predisposed to the disorder.

“Our results clearly are not definitive … but [they] are consistent with the hypothesis, and, therefore, further research focused on establishing whether such a trigger exists and on identifying it is warranted,” said Michael Waldman, Ph.D., of the Johnson Graduate School of Management, Cornell University, Ithaca, N.Y., and his associates.

The investigators noted that several state surveys overseen by the U.S. Department of Education and a recent Centers for Disease Control and Prevention study all indicated that autism prevalence is higher in certain northern regions of the country, and lower in dry areas of the south and southwest.

They assessed a possible correlation with precipitation in Washington, Oregon, and California, where regions west of the mountains receive almost four times as much precipitation as do regions to the east. Using regression analysis, the investigators found that autism prevalence was higher in counties that received abundant precipitation. It also was higher for birth cohorts that received above-average precipitation relative to the usual amount in that county, Dr. Waldman and his associates said.

“The magnitude of the measured relationships is substantial,” they noted (Arch. Pediatr. Adolesc. Med. 2008;162:1026-34).

They are not proposing that autism is related to rain and snow per se, but that it may be related to indoor activities or exposures that are increased during bad weather.

For example, early, excessive television and video viewing has been associated with psychopathological traits such as poor language and cognitive development. It may be that this exposure produces only mild health consequences in most children but produces more serious problems such as autism in genetically vulnerable children.

“Another possibility is that vitamin D deficiency is an environmental trigger for autism,” the researchers wrote. Higher precipitation means less exposure to sunshine, the major source of vitamin D, and vitamin D deficiency “can lead to reduced levels in the developing brain of calcitriol, a critical neurosteroid involved in brain development,” they added.

Any environmental trigger that is associated with indoor activities could be at fault, including household chemicals. And it also is possible that precipitation is more directly involved, by transporting chemicals in the upper atmosphere to the ground, for example. Or high precipitation may promote the overgrowth of weeds or expansion of the insect population, which in turn increase the use of pesticides, they wrote.

In an accompanying editorial, Dr. Noel S. Weiss of the University of Washington, Seattle, noted that the study findings are “tentative” and were intended to prompt further research into environmental triggers, not to implicate rainfall itself.

“The primary audience of Waldman et al is not the practicing pediatrician, and certainly, it is not a member of the public at large. These individuals cannot take away any practical message from it. Rather, the primary target is an investigator interested in the causes of autism, someone who might be able to test one or more of the etiologic hypotheses that derive from [the study],” he said (Arch. Pediatr. Adolesc. Med. 2008:162;1095-6).

The researchers “have made it clear that the message the public should take from their data regarding precipitation and autism is … 'No call for alarm, stay tuned,'” Dr. Weiss wrote.