A growing body of scientific research has now found that Vitamin D deficiency may potentially play a role in the etiology and development of ASD(Autism Spectrum Disorder).
Autism spectrum disorder (ASD) is a developmental disorder characterized by pervasive deficits in social interaction, impairment in verbal and non-verbal communication, and stereotyped patterns of interests and activities.
In this article, I’m going to highlight some of the latest cutting-edge research on the link between Vitamin D status and the development of Autism Spectrum Disorder.
An increasing amount of evidence points to the possibility that gestational and early childhood vitamin D deficiency cause some cases of autism. 
Two open-label trials found high dose vitamin D improves the core symptoms of autism in about 75% of autistic children. A few of the improvements were remarkable.
These two open-label trials were recently confirmed with a randomized controlled trial (RCT) using 300 IU/kg/day with a maximum of 5000 IU/day and resulted in effects similar to the two open-label studies. 
In terms of prevention, a recent small study showed vitamin D supplementation during pregnancy (5000 IU/day) and during infancy and early childhood (1000 IU/day) significantly reduced the expected incidence of autism in mothers who already had one autistic child from 20% to 5%. 
The 2017 study published in the reviews in endocrine and metabolic disorders concluded:
Vitamin D is safe; for example, over the last 15 years, Poison Control reports there have been approximately 15,000 cases of vitamin D overdose. However, only three of these 15,000 people developed clinical toxicity and no one died.
Given those facts, practitioners might consider treating autism with 300 IU/kg/day, and seek to prevent autism by supplementing pregnant and lactating women (5000 IU/day) and infants and young children (150 IU/kg/day) checking 25(OH)D levels every 3 months.
These doses will increase 25(OH)D blood levels to those recommended by the Endocrine Society. As the American Academy of Pediatrics recommends vitamin D supplementation during infancy and childhood, pediatricians and family practitioners should evaluate the current evidence on autism and vitamin D and act accordingly.
 Vitamin D and autism, what’s new?
 Vitamin D status in autism spectrum disorders and the efficacy of vitamin D supplementation in autistic children.
 Clinical improvement following vitamin D3 supplementation in Autism Spectrum Disorder.
 Is high prevalence of Vitamin D deficiency evidence for autism disorder?: In a highly endogamous population
The information in this article has not been evaluated by the FDA and should not be used to diagnose, cure or treat any disease, implied or otherwise.