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

: 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. : 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. : 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. : 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.