Vitamin D supplementation in the first 2 years and autism spectrum traits at 6-8 years - a randomized clinical trial.

This was a randomised controlled trial — people were assigned to treatments by chance, which is the most reliable way to tell whether a treatment itself caused a change.

It involved 366 people, a reasonably sized group for this kind of research.

The researchers concluded: "We found no indication that higher-than-normal vitamin D3 supplementation between ages 0 and 2 years decreases ASD-related trait scores at ages 6-8 years. Sex-stratified analysis suggested an inverse association, among boys, between early life 25(OH)D concentrations and ASD-related traits, warranting further studies on potential causal direction and sex specificity of associations."

This record does not state:

• how long the study ran

This is a plain-language summary of one paper's abstract, not medical advice. Talk to your child's clinician before changing anything.

Journal: Journal of child psychology and psychiatry, and allied disciplines

Year: 2026

Design: Randomized Controlled Trial

Participants: 366

Age range: 6-8 years

Intervention: vitamin D

Authors: Samuel Sandboge, Vilja Seppälä, Sakari Lintula, Elisa Holmlund-Suila, Helena Hauta-Alus, Eero Kajantie, Outi Mäkitie, Sture Andersson, Katri Räikkönen, Kati Heinonen

BACKGROUND: Early life vitamin D levels may be associated with autism spectrum disorder (ASD) and related traits, but causality is unknown. We examine whether higher-than-standard vitamin D3 supplementation during the first 2 years, as well as higher pregnancy and childhood 25-hydroxyvitamin D (25(OH)D) levels and their trajectories, are associated with lower ASD trait scores at ages 6-8 years in a non-clinical cohort. METHODS: This secondary analysis of the double-blind randomized clinical trial vitamin D intervention in infants (VIDI) comprised 366 Finnish children aged 6-8 years, 177 of whom were randomized to receive 400-IU and 189 to receive 1,200-IU daily oral vitamin D3 supplementation between ages 2 weeks and 2 years. ASD-related traits were assessed at mean age 7.2 years (SD 0.4) using the parent-reported Autism Spectrum Screening Questionnaire (ASSQ). Predictor variables were supplementation group, 25(OH)D concentrations measured during pregnancy and at ages 1 and 2 years, as well as 25(OH)D trajectories (high vs. low) derived from these time points. RESULTS: None of the predictor variables of interest were associated with the outcome in the full sample. After sex stratification, among boys, 25(OH)D concentrations at 1 and 2 years were inversely associated with ASSQ scores (mean difference -0.2 of normalized SD score (95% CI -0.3 to -0.1, p = .003) and -0.2 (95% CI -0.3 to -0.05, p = .01) per 10 ng/mL 25(OH)D) after adjustment for age, breastfeeding, parental education, maternal depressive symptoms, and season of 25(OH)D assessment as was belonging to the higher 25(OH)D trajectory, -0.45 SD (95% CI -0.79 to -0.10, p = .01). CONCLUSIONS: We found no indication that higher-than-normal vitamin D3 supplementation between ages 0 and 2 years decreases ASD-related trait scores at ages 6-8 years. Sex-stratified analysis suggested an inverse association, among boys, between early life 25(OH)D concentrations and ASD-related traits, warranting further studies on potential causal direction and sex specificity of associations.

Journal of child psychology and psychiatry, and allied disciplines, 2026

PMID 41486975

DOI 10.1111/jcpp.70110

This record was extracted from the paper's PubMed abstract and metadata. Full-text methods and risk-of-bias details were not reviewed.