New research indicates that pregnant women who have been exposed to a pesticide found in the food chain have an increased risk in bearing children with autism.
The research looked at data gathered from the Finnish Prenatal Study of Autism, a national birth cohort study, to examine the levels of DDE (dichlorodiphenyl dichloroethylene) in pregnant women.
DDE is a breakdown product of the pesticide DDT, which was banned in many countries decades ago. However, DDT can still be found in the food chain, which results in continuous exposure among some populations. And since chemicals can transfer across the placenta, children may also be at risk of prenatal exposure.
DDT was developed as the first of the modern synthetic insecticides in the 1940s. It was initially used to combat malaria, typhus, and the other insect-borne human diseases among both military and civilian populations. It was also effective for insect control in crop and livestock production. In the late 1950s and 1960s, it was banned in various countries because of mounting evidence of the pesticide's declining benefits and environmental and toxicological effects.
"We think of these chemicals in the past tense, relegated to a long-gone era of dangerous 20th Century toxins," said lead study author Alan S. Brown. "Unfortunately, they are still present in the environment and are in our blood and tissues. In pregnant women, they are passed along to the developing fetus. Along with genetic and other environmental factors, our findings suggest that prenatal exposure to the DDT toxin may be a trigger for autism."
Carried out by researchers at Columbia University along with the University of Turku and the National Institute for Health and Welfare, Finland, the study looked at data from the Finnish Prenatal Study of Autism, which contained a million cases of Finnish women who gave birth between 1987 and 2005.
The new research, published in the American Journal of Psychiatry, looked at 778 children with autism and 778 children without autism who acted as control subjects. They measured the levels of DDE and DDT in blood serum samples taken from the mothers during early pregnancy.
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After taking into account the mother's age and other possible factors, the results showed that the chance of a child having autism was significantly increased if the mother had an elevated level of DDE, defined as the 75th percentile or greater.
"In addition, the odds of children having autism with intellectual disability were increased more than twofold with maternal DDE levels above this threshold," noted a statement from the American Psychiatric Association.
"We showed that overall in autism, there was a modest increase in risk, but the vast majority of offspring who are exposed to the high levels still won't get autism," said Dr. Brown.
The researchers also examined the levels of PCBs (polychlorinated biphenyls), which are chemicals used in industrial application, but found no association between the chemicals and autism in children.
The authors concluded that their findings "provide the first biomarker-based evidence that maternal exposure to insecticides is associated with autism among offspring."
They noted that the study contributes to the understanding of autism and has implications for preventing the disorder. However, they added, the results do not prove causation, and further research is necessary.
Dr. Brown, who is also a professor of psychiatry and epidemiology at NYC's Columbia University Medical Center, encourages pregnant women or those who are planning to bear children to eat organic produce.
With files from Charmaine Noronha.
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