A Comprehensive Review of Autism Spectrum Disorder: Mechanisms, Modifiable Factors, and Clinical Implications — A Focus on Vitamin D

Autism Spectrum Disorder (ASD) is a multifactorial neurodevelopmental condition influenced by complex genetic, epigenetic, and environmental factors. Among the modifiable biological factors under investigation, Vitamin D has gained increasing attention for its potential role in neurodevelopment and immune regulation. Evidence indicates that Vitamin D deficiency is highly prevalent in individuals with ASD and may contribute to altered neuroimmune respons-es, impaired neurotransmission, oxidative stress, and atypical brain development. This review synthesises current findings on the association between Vitamin D status and ASD, highlighting observational studies, mechanistic evidence, and interventional trials. Several clinical studies report that correcting Vitamin D deficiency, particularly during pregnancy or early childhood, may lead to improvements in behavioural, cognitive, and emotional symptoms, although re-sults vary depending on dosage, baseline levels, and duration of supplementation. Given its safety profile and biological plausibility, optimising Vitamin D levels represents a low-risk, potentially beneficial strategy within comprehensive ASD care. Nonetheless, further high-quality randomised controlled trials are required to clarify causality, determine effective supplementation protocols, and better understand the underlying mechanisms linking Vitamin D to ASD neurobiology.