Occurrence and Correlates of Vitamin D and Iron Deficiency in Children with Autism Spectrum Disorder

Background/Objectives: This study aimed to determine the occurrence of vitamin D and iron deficiency in children with autism spectrum disorder (ASD) in Singapore and identify correlates of the presence of these deficiencies, if any. Methods: This is an observational, cross-sectional, retrospective review of children with a diagnosis of autism, aged 1 to 10 years old, seen at a tertiary developmental paediatric centre from January 2018 to December 2022, with blood investigations completed. Autism diagnosis was determined either clinically by a developmental paediatrician using DSM-5 criteria or using the Autism Diagnostic Observation Schedule (ADOS-2). Children with genetic disorders and chronic medical conditions were excluded. Logistic regression was used to evaluate associations with the deficiencies, and the Bonferroni method was applied on post hoc comparisons. Results: The overall sample comprised 241 children (79% males, mean age 4.2 years [SD 2.25]. There were 222 and 236 children who had blood investigations for vitamin D and iron levels performed, respectively. Out of the 222 children whose vitamin D tests were performed, 36.5% had vitamin D insufficiency/deficiency. Iron deficiency occurred in 37.7% for children who had their iron levels tested. There were 122 observations for both iron levels and complete blood count. Out of these, 19 (15.6%) had iron deficiency anaemia. There were no significant correlates for iron deficiency, with picky eating included. Conclusions: Vitamin D and iron deficiencies were common in this sample. Clinicians should consider testing for vitamin D and iron for children with ASD, especially for vitamin D in children of Indian ethnicity and older age.