The effect of vitamin D supplementation in treatment of children with autism spectrum disorder: a systematic review and meta-analysis of randomized controlled trials

Objective: The effect of vitamin D supplementation on the risk of Autism Spectrum Disorder (ASD) is conflicting. The aim of this study was to estimate the efficacy of vitamin D supplementation on ASD in children.Methods: We conducted a meta-analysis of randomized controlled trials (RCTs) in which vitamin D supplementation was used as a therapy in children with ASD. The PubMed, PsychINFO, Cochrane CENTRAL library, Web of Science, and Cinahl databases were searched from inception to March 20, 2019, for all publications on vitamin D and ASD with no restrictions. Studies involving individuals aged <18 years diagnosed with ASD and with all functional outcomes assessed by measurement scales for ASD were included. Mean differences were pooled, and a meta-analysis was performed using a random-effects model due to differences between the individual RCTs.Results: There were five RCTs with 349 children with ASD in the review, of which three RCTs were included in the meta-analysis. Vitamin D supplementation indicated a small but significant improvement in hyperactivity scores (pooled MD: -3.20; 95% CI: [-6.06, -0.34]) with low heterogeneity (I2  = 10%, p = 0.33), but there were no other statistically significant differences in ASD symptoms between groups as measured by validated scales.Conclusion: Vitamin D supplementation appears to be beneficial for hyperactivity but not for core symptoms or other co-existing behaviors and conditions of ASD. Future RCTs with large sample sizes examining the effect of vitamin D supplementation on ASD among individuals with low serum vitamin D levels at baseline are needed.