Vitamin D and Autism Spectrum Disorder

Abstract

1,25(OH)2D is the hormonally active form of vitamin D known for its pleiotropic immunomodulatory effects. Via altering gene transcription, 1,25(OH)D exerts immunosuppressive effects and stimulates immune regulation. Recently, the interest in vitamin D in association with autism spectrum disorder (ASD) has been triggered. The prevalence of ASD has increased excessively over the last few decades, emphasizing the need for a better understanding of the etiology of the disorder as well as to find better treatments. Vitamin D levels in ASD patients are observed to be lower compared to healthy individuals and maternal vitamin D deficiency has been associated with an increased risk of ASD. Moreover, vitamin D supplementation improves ASD symptoms. These recent clinical findings strongly suggest that vitamin D is a factor in ASD onset and progression. Yet, possible mechanisms behind this association remain unknown. This review summarizes immunomodulatory properties of vitamin D and peripheral immune dysregulation in ASD, after which possible mechanisms via which vitamin D could rebalance the immune system in ASD are discussed. Although promising clinical results have been found, further research is necessary to draw conclusions about the effect and mechanisms behind the effect of vitamin D on ASD development.