Blunted serum 25(OH)D response to vitamin D supplementation in children with autism.

Data suggest a potential role for vitamin D in autism spectrum disorder (ASD) prevention and treatment. It is likely that the serum response to vitamin D supplementation contributes to its effectiveness. Multiple factors affect serum vitamin D 25(OH)D response to supplementation. We conducted post-hoc analysis of two double-blind, randomized, placebo-controlled trials (RCT) of vitamin D supplementation, one RCT involving children with ASD and another involving children with asthma. Both trials were conducted in the same geographic location (Dublin, Ireland, 53°N), conducted over Winter season and utilized the same vitamin D dose (2000 IU/day). We included 18 children with ASD and 17 children with asthma. There was no significant difference in 25(OH)D or age at baseline, however, BMI was significantly lower in ASD ( = 0.03). Compliance with vitamin D supplementation was high in both trials. Despite a significantly longer intervention period (20w vs. 15w;  < 0.0001), ASD children had a significantly lower absolute increase (+26 vs. +45 nmol/l) in 25(OH)D ( = 0.04). Despite similar demographics, children with ASD had a lower increase in 25(OH)D levels with supplementation. Potential mechanisms include altered absorption/metabolism as well as well genetic factors. Clinical and research work relating to vitamin D is ASD should measure 25(OHO)D response to supplementation to assess therapeutic doses.