Autism spectrum disorder (ASD) is a pervasive developmental disorder with heterogeneous etiology.
Vitamin D can function as a fat-soluble vitamin as well as a hormone, and can exert its effect through both genomic
and non-genomic mechanisms. In the last decades, several studies have examined the relationship between
vitamin D levels and ASD. These studies demonstrated that low vitamin D status in early development has been
hypothesized as an environmental risk factor for ASD. Both in vivo and in vitro studies have demonstrated that
vitamin D deficiency in early life can alter brain development, dysregulates neurotransmitter balance in the brain,
decreases body and brain antioxidant ability, and alters the immune system in ways that resemble pathological
features commonly seen in ASD. In this review, we focused on the association between vitamin D and ASD. In
addition, the above-mentioned mechanisms of action that link vitamin D deficiency with ASD were also discussed.
Finally, clinical trials of vitamin D supplementation treatment of ASD have also been discussed.