Long-thought cause of autism not linked to symptoms, study finds

Exposure to toxic pesticides in the womb may not actually be linked to autism symptoms, a new study suggests.  

As autism now affects one in 31 American children, a stark increase from one in 150 in the early 2000s, experts are searching for potential causes and screening tools to catch the condition sooner. 

Among those most studied are environmental pollution and the use of pesticides used in farming that infiltrate the food supply, particularly fruits and vegetables. 

Scientists have long suspected that these chemicals trigger inflammation in the brain and alter levels of neurotransmitters like dopamine and serotonin, leading to hallmark characteristics such as communication difficulties and hyperactivity. 

However, in a new study examining pairs of mothers and children exposed to organophosphate pesticides, which are known to be toxic to humans, during pregnancy, researchers at NYU Langone in New York City found no significant relationship between the toxins and autism-related traits in their children. 

It’s unclear what exactly led to the results, but the researchers suggested that the benefits of a diet high in fruits and vegetables, such as reduced inflammation, may offset the potential harms of pesticides.

The team said that while the findings do not conclusively prove that pesticides are safe for children and pregnant women, they do suggest pesticides and autism may not be related.

They noted future studies may help inform policies and restrictions surrounding pesticides, which have also been linked to neurological conditions like Parkinson’s disease and several forms of cancer. 

‘While we know that organophosphate pesticides can harm the developing brain, they were not a major driver of characteristics seen in autism at the relatively low exposure levels we observed,’ Dr Haleigh Cavalier, lead study author and doctoral student at NYU Langone Health’s Departments of Population Health and Pediatrics, said. 

‘These results should not be interpreted to mean that such pesticides are safe, nor do they rule out autism-related risks at higher exposures or among more vulnerable groups.’

The study, published in JAMA Pediatrics, looked at data from 3,339 pairs of mothers and children enrolled at 20 medical centers in the US National Institutes of Health’s Environmental Influences on Child Health Outcomes (ECHO) Program, a nationwide study that examines the impact of environmental, social and biological factors on a child’s health.

The researchers measured levels of metabolites, byproducts of chemical breakdown in the body, in urine samples during pregnancy. The tests revealed 99 percent of mothers had detectable levels of organophosphate pesticides in their urine. 

The team then looked for associations between metabolite levels and how the children scored on the Social Responsiveness Scale, a 65-item questionnaire designed to identify social communication issues and autism-related traits such as eye contact avoidance, difficulty understanding people’s emotions and needing to follow specific routines.

Children were evaluated between five and seven years old on average. 

There were no consistent associations between the levels of metabolites detected in urine and autism-related traits when adjusting for sex and dietary factors, the study found. 

The authors note that one limitation is that metabolites are short-lived in the human body, so exact levels can vary over time. Additionally, individual metabolism can impact levels. 

This means the markers may not provide the full picture in terms of pesticide exposure, but additional studies may strengthen the findings.

‘Our results demonstrate that there is still much more to be learned about autism,’ Dr Akhgar Ghassabian, senior study author and associate professor in the Department of Pediatrics at the NYU Grossman School of Medicine, said.

‘Careful, long-term research can help clarify which environmental exposures matter most so that communities and policymakers can make more informed decisions.’