Denmark: Researchers from the University of Copenhagen reported in their original research article that their study revealed a reduced risk of autism, a lower load of autistic symptoms, and a decreased risk of ADHD diagnosis for mothers with higher levels of 25(OH)D before starting the intervention. However, high-dose vitamin D3 supplementation during pregnancy had no impact on the risk of autism or ADHD.

This investigation is published in the American Journal of Clinical Nutrition.
During pregnancy, a deficiency of vitamin D may lead to a higher likelihood of developing autism or attention deficit hyperactivity disorder (ADHD).
This study aimed to determine the impact of vitamin D3 supplementation during pregnancy on the risk of developing autism and ADHD.
This randomized clinical trial was conducted as part of the COPSYCH project, which is nested within the COPSAC2010 cohort, a population-based sample of 700 healthy mother-child pairs (enrolled at week 24 of pregnancy). The maternal 25-hydroxy-vitamin D (25(OH)D) levels were measured, and 623 mothers were randomly assigned to receive either high-dose (2800 IU/d) or standard-dose (400 IU/d) vitamin D3 until one week after giving birth (315 received high-dose, 308 received standard-dose). When the children reached the age of 10, the diagnoses and symptom load of autism and ADHD were assessed using the Kiddie Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime Version (K-SADS-PL).
Key summary points are:
At ten years of age, a total of 591 children completed the psychopathological evaluation.
2.7 % (16 children) were diagnosed with autism.
11 % (65 children) were diagnosed with ADHD.
Of the 496 children in the vitamin D3 trial, 246 received high doses, and 250 received standard doses. Twelve children with autism and 58 with ADHD were diagnosed among them.
Higher maternal pre-intervention 25(OH)D levels were linked to lower risk of autism (OR per 10 nmol/L 0.76), reduced autistic symptom load (β per 10 nmol/L -0.03), and reduced ADHD diagnosis risk (OR per 10 nmol/L 0.88).
There was no association between High-dose vitamin D3 supplementation and autism or ADHD risk.
They said that higher maternal pre-intervention 25(OH)D reduces autism risk, ADHD diagnosis and autistic symptom load, but high-dose vitamin D3 does not affect these outcomes in pregnancy.
Lundbeck Foundation, the Ministry of Health, and the Danish Council for Strategic Research funded the study.
Reference:
Aagaard, K et al. High-dose vitamin D3 supplementation in pregnancy and risk of neurodevelopmental disorders in the children at age 10 - A randomized clinical trial. The American Journal of Clinical Nutrition.