New US research has found that children exposed to common agricultural pesticides before birth and in their first year of infancy may have a small to moderately increased risk of autism spectrum disorder (ASD) compared to unexposed children.
Carried out by researchers at the University of California, the new study looked at 2,961 patients with a diagnosis of ASD -- including 445 with ASD with accompanying intellectual disability -- and 35,370 healthy patients matched for birth year and sex, who were all born between 1998 and 2010 in Central Valley, California, a heavily agricultural region.
The researchers assessed the participants' prenatal exposure and exposure as infants to 11 pesticides, selected because they are commonly used and thought to have a toxic effect on brain development.
Exposure to the pesticides was measured as pounds of pesticides applied per acre per month within 2 km of their mother's residence during pregnancy and during developmental periods.
The findings, published in The BMJ, showed that after adjusting for potentially influential factors, the children exposed to several pesticides (including glyphosate, chlorpyrifos, diazinon, malathion, permethrin, bifenthrin and methyl-bromide) before birth and during the first year of life had a modest increase in their risk of ASD, compared with the controls.
In addition, the associations was found to be strongest in those with ASD and intellectual disability, which represents the more severe end of the autism spectrum.
Although previous studies have found evidence to suggest the common pesticides can negatively affect brain development, and that exposure in early life may increase a child's risk of ASD, the researchers point out that studies which look at the link between pesticide exposure in the real world and risk of ASD are rare.
They add that although the new study cannot establish cause and effect, it, the largest so far to investigate pesticides and ASD, backs up previous studies in this area.
They note that further research is now needed but add that the findings support efforts to prevent exposure to pesticides during pregnancy to help protect a child's developing brain.