The effect of vitamin D supplementation on individuals with autism spectrum disorder (ASD) is inconclusive. We aimed to conduct a meta-analysis of the available randomized controlled trials (RCTs) to explore whether vitamin D supplementation can improve core symptoms and coexisting conditions in children with ASD. Data were obtained by searching the PubMed, Embase, Web of Science, CINAHL and Cochrane Library databases up to February 2022 following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Using a random-effects model, mean differences with 95% confidence intervals (CIs) were calculated through a meta-analysis. There were eight RCTs with 266 children with ASD in the present review, among which six RCTs were included in the meta-analysis. Children who received vitamin D supplementation showed a significant improvement in stereotypical behavior scores (pooled mean difference (MD): -1.39; 95% CI: -2.7, -0.07; P = 0.04) with low heterogeneity (I2 = 34%), and there was a trend toward decreased total scores on the Social Responsiveness Scale (SRS) and Childhood Autism Rating Scale (CARS, P = 0.05); however, there were no other significant differences in the core symptoms of ASD and coexisting conditions between groups as measured by the Aberrant Behavior Checklist (ABC). Vitamin D supplementation appears to improve stereotypical behaviors but does not improve other core symptoms and coexisting conditions. Further randomized controlled trials with large sample sizes and individualized doses are needed.
Keywords: Autism spectrum disorder; Children; Core symptoms; Meta-analysis; Vitamin D intervention.