Autism spectrum disorder and low vitamin D at birth: a sibling control study

Observational, sibling-control study. 58 Sweden-born children formed ASD and non-ASD sibling pairs across two cohorts: Gothenburg (47 pairs) and Stockholm Somali (11 pairs). ASD diagnosed in early childhood (including autism, atypical autism, and Asperger syndrome); non-ASD siblings aged 4 years or older. Neonatal dried blood spots were used to measure total 25(OH)D via LC-MS/MS; laboratory analysts were blinded to diagnosis.

ASD siblings had lower neonatal 25(OH)D than non-ASD siblings (mean 24.0 nM, SD 19.6 vs 31.9 nM, SD 27.7; n=58 vs 57; P=0.013; bootstrap P=0.026; 95% CI for mean difference 2.24–14.21). The difference was not fully explained by season of birth; significance observed in Swedish and Miscellaneous ethnic groups but not in African/Middle East group due to a floor effect. All Somali-origin children had vitamin D deficiency. The pattern suggests low prenatal vitamin D may be a risk factor for ASD, warranting replication; future work should assess whether prenatal vitamin D supplementation reduces ASD risk.

Small sample size; gender imbalance with a male-predominant ASD group; two cohorts with differing ethnic backgrounds limit generalizability; African/Middle East group had universal deficiency limiting comparisons; non-ASD siblings were not clinically reassessed; potential late ASD diagnoses among siblings; possible residual confounding by maternal lifestyle or infections; vitamin D status measured only at birth.