Maternal serum 25-hydroxy vitamin D levels and risk of autism spectrum and attention-deficit hyperactivity disorders in offspring: A systematic review and dose-response meta-analysis

•This systematic review and meta-analysis of epidemiological studies found significant inverse associations between maternal serum vitamin D levels with offspring ASD and ADHD when the highest versus the lowest level of maternal serum 25(OH)D was compared.•Dose-response analyses indicated that each 25 nmol/L (or 10 ng/mL) increment in maternal serum vitamin D was associated with 19% and 18% reduced risk of offspring ASD and ADHD, respectively.•Maternal serum vitamin D level of more than 30 nmol/L was associated with lower odds of offspring ASD. However, a nonlinear U-shaped association was observed between maternal serum vitamin D levels and offspring ADHD risk.