Autism Study Finds Link With Pregnancy Diet

Mothers’ diets during pregnancy may affect their child’s likelihood of developing autism, new research suggests.

Autism spectrum disorders are a diverse group of conditions characterized by some degree of difficulty with social interaction and communication, affecting roughly 1 in 36 children in the U.S., according to the U.S. Centers for Disease Control and Prevention.

“Based on current understanding, autism is thought to be caused by a combination of genes and environmental factors,” Catherine Friel, a dietitian and post-doctoral researcher at Scotland’s University of Glasgow, told Newsweek.

“However, the exact mechanisms are not fully understood, and in addition to prenatal diet, many environmental factors have been related to autism, such as nutritional supplements, maternal BMI, environmental toxins, medications and illness/infection,” she said.

Potential mechanisms, Friel said, may involve “maternal immune activation, maternal microbiome and genetics. In reality, though, current evidence of these pathways is fragmented and incomplete. Thus, we have ideas and theories as to the cause of autism, but more evidence is required to fully piece this together with certainty.”

Studies have shown that prenatal multivitamins and folic acid supplement use, as well as adequate vitamin D and high fish intake, are all associated with a reduced likelihood of childhood autism diagnoses. However, considering these factors in isolation neglects the synergistic and antagonistic effects that nutrients can have when consumed as part of a realistic prenatal diet.

To date, studies into these holistic associations have been based on small sample sizes, with inconsistent results. Now, for the first time, Friel and her colleagues at the University of Glasgow have conducted a large study of over 95,000 mothers and their children to determine whether there is a statistically significant association between maternal diet quality and their baby’s likelihood of developing autism.

Data was gathered from two large prospective cohort studies: the Norwegian Mother, Father and Child Cohort Study and the Avon Longitudinal Study of Parents and Children, in England. Data was collected from 2002 to 2008 and 1990 to 1992, respectively, and children were followed up until the age of 8 or older.

Diet quality was assessed based on global dietary guidelines, including a high intake of fruits, vegetables, fish, nuts and whole grains and a low intake of red and processed meats, soft drinks and foods high in saturated fats and refined carbohydrates. Participants were then categorized as having high adherence to healthy dietary patterns, medium adherence and low adherence.

After adjusting for potentially confounding factors, such as maternal BMI (body mass index), education levels and supplement use, a high adherence to healthy dietary patterns during pregnancy was associated with a 22 percent reduction in the likelihood of the child being diagnosed with autism. High adherence was also associated with a 24 percent lower likelihood that the child would go on to develop social communication difficulties.

The associations were particularly strong among mothers with baby girls.

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Exactly why we see these associations is not completely clear, although the researchers have suggested that prenatal diets may affect DNA expression and regulate immune processes.

Diet is complex and contains a huge array of bioactive components, which some researchers have estimated to be as high as 26,000. There may be specific effects with nutrients—for example, their specific role in neural formation or their antioxidant and anti-inflammatory effects or influence on immunoregulation. But there could also be global effects, such as the effect of a healthy diet contributing to good maternal health.

However, the researchers stressed that these results are purely observational. “At present, we remain uncertain as to whether the associations observed are causal,” they write.

There may also still be confounding factors that were not accounted for in the analysis, such as genetics, parental caregiving and childhood diets. “We cannot be certain that all confounding bias is accounted for,” the researchers said.

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Even if a causal relationship is found, maternal diets are not the only factor influencing a child’s likelihood of developing autism. It is estimated that around 80 percent of autism cases can be linked to inherited genetic mutations.

In other words, a mother could follow a perfectly balanced, healthy diet and still see her child receiving an autism diagnosis.

“Further research should substantiate our findings, especially given the inconsistency in the previous literature,” the researchers write.

The full study can be read in the journal JAMA Network Open.

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Update 7/22/24, 11: 14 a.m. ET: This article was updated to include a comment from Catherine Friel.

Updated 7/24/23, 05: 45 a.m. ET: This article was updated to include Catherine Friel’s full title.