The impact of maternal vitamin D levels during pregnancy and risk of autism spectrum disorder and attention deficit hyperactivity disorder diagnosis and symptoms in offspring: a systematic review and dose-response meta-analysis

Introduction: Autism Spectrum Disorder (ASD) and Attention Deficit Hyperactivity Disorder (ADHD) have a complex etiology involving both genetic and environmental factors, with mechanisms still unclear. In this review, we investigated the association between maternal 25-hydroxyvitamin D status during pregnancy and the risk of diagnosis and symptoms of ASD and ADHD in offspring in developmental age. Methods: We searched online databases up to February 13, 2026. We conducted a quantitative meta-analysis by comparing the exposure categories and using a dose-response approach across the entire exposure range. Results: We included 15 eligible studies: 8 related to ASD and ASD symptoms, 5 related to ADHD and ADHD symptoms, and 2 to both. Comparing high versus low maternal vitamin D status, we found an inverse association with both lower ASD risk (RR = 0.91; 95% CI 0.87-0.96) and ADHD risk (RR = 0.90; 95% CI 0.82-0.99). In the dose-response pooled analysis, ASD risk linearly decreased by 9% for every 10 nmol/L increase in maternal serum vitamin D levels. Higher vitamin D levels were also inversely associated with ADHD symptoms, though estimates were statistically imprecise due to the limited number of studies. Conclusions: Higher vitamin D status during pregnancy appears to be linearly associated with a reduced risk of ASD and ADHD diagnoses and symptoms in offspring, with no evidence of thresholds across the investigated exposure range. These findings suggest the opportunity to assess vitamin D levels during pregnancy, and to consider its supplementation in deficiency cases, to support fetal brain development and promote neuroprotection.