Vitamin D and Autism Spectrum Disorder
Vitamin D has been examined as a factor in autism spectrum disorder (ASD) both prenatally (maternal levels and offspring risk) and postnatally (as a possible adjunct in ASD children who happen to be deficient). The evidence is preliminary and marketing has run ahead of the science.
Prenatal maternal 25(OH)D
A 2019 Australian cohort (Vinkhuyzen) reported children born to mothers with 25(OH)D < 25 nmol/L at 20 weeks gestation had higher rates of autism-related traits at age 6. The 2020 Danish register study (Sourander) found similar signals. Mendelian randomisation studies have been mixed and do not definitively support causation. Adequate prenatal vitamin D is a reasonable general recommendation independent of the ASD question.
Deficiency in ASD children
Cross-sectional studies find children with ASD have lower 25(OH)D than typically developing peers — likely from a combination of restrictive eating patterns, reduced outdoor play, and (in some cases) shared genetic risk factors. Approximately 50–70% of ASD children have insufficient or deficient 25(OH)D in several cohorts.
Supplementation trials
- Saad 2018 (Egypt) — 109 ASD children; 300 IU/kg/day (max 5,000 IU) for 4 months significantly improved Childhood Autism Rating Scale (CARS) scores vs placebo in deficient children.
- Feng 2017 — 215 ASD children; 150,000 IU IM monthly + 400 IU/day oral × 3 months improved core symptoms.
- 2019 meta-analysis — trials to date show modest signal but heterogeneous designs and small samples; not enough to establish standard clinical practice.
Where to be careful
Some ASD supplement protocols promoted online use pharmacologic doses (up to 15,000 IU/day) or add several other agents (omega-3, methyl-B12, folinic acid) in complex regimens marketed for large sums. These protocols are not standard of care; RCT evidence for such stacks is limited or absent, and hypercalcaemia can occur with the higher vitamin D doses.
Practical guide
- Test 25(OH)D in ASD children, especially those with restrictive eating patterns.
- Correct deficiency with standard paediatric dosing (600–2,000 IU/day cholecalciferol depending on age and baseline).
- Continue guideline-based ASD interventions — early intensive behavioural intervention (ABA, ESDM), speech and language therapy, occupational therapy.
- Do not use vitamin D as a rationale for delaying or replacing evidence-based ASD care.