Maternal Dietary Factors and the Risk of Autism Spectrum Disorders: A Systematic Review of Existing Evidence.
Caichen Zhong, Jillian Tessing, Brian K Lee and 1 others
PMID 33015977WHAT IT FOUND
Prenatal folic acid and vitamin D show the most consistent links to reduced autism risk, but results vary by study type.
Folate supplements often show protection, while blood tests do not. Evidence for fish, iron, and other nutrients is too limited or conflicting to guide practice.
Key findings
01Higher or moderate intake of most nutrients examined was associated with reduced odds of ASD, though these were not uniformly statistically significant.
02For folic acid, studies relying on self-reported supplementation support an inverse association with ASD, while all studies relying on folate biomarkers reported null associations.
03The weight of evidence supports a protective association between higher vitamin D levels and ASD or ASD-related traits, though discrepancies exist in the strength of the association.
STILL TO COME
How it was doneWhat they found
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What it does not show
Substantial heterogeneity in how dietary factors were measured (self-report vs. biomarkers) and how ASD was defined. Many studies relied on retrospective self-reporting, which is prone to recall bias. Approximately 50% of studies lacked biomarker data, and those that had it often measured nutrients outside the suspected critical windows. Confounding factors such as overall health and other dietary habits were not consistently adjusted for across studies. The review excluded ecological studies and case reports, limiting the scope to observational designs with comparison groups.
Declared interests
The authors declare no conflict of interest.
The easy way to misread this
Do not interpret the protective associations with folic acid supplements as proof of causation. The discrepancy between supplement use data and blood biomarker data suggests that women who take supplements may differ in other health behaviors, or that the timing of measurement misses the critical window.