To investigate the differences of intestinal flora in Vitamin D adequacy and deficiency groups of children with autism spectrum disorder(ASD) and the correlation between serum total 25-hydroxyvitamin D [T-25(OH)D] levels and intestinal flora.

ASD children who attended the outpatient clinic of the department of Rheumatology and Clinical Immunology of Peking Union Medical College Hospital during October 2009 and February 2022 were retrospectively included in the study. According to the serum T-25(OH)D levels, they were divided into Vitamin D adequacy group[T-25(OH)D > 30 μg/L], Vitamin D insufficiency group[20 μg/L≤T-25(OH)D≤30 μg/L] and Vitamin D deficiency group[T-25(OH)D < 20 μg/L].Serum T-25(OH)D levels were measured using liquid chromatography-tandem mass spectrometry. Human gut metagenome data from these children with ASD were analyzed using bioinformatics methods.

46 children with ASD who met the inclusion and exclusion criteria were included in the study. The numbers of patients in Vitamin D adequacy group, Vitamin D insufficiency group and Vitamin D deficiency group were respectively 15, 16 and 15. Linear discriminant analysis revealed that the bacteria abundance of Bilophila wadsworthia, Adlercreutzia equolifaciens, Asaccharobacter celatus and Escherichia coli were significantly enriched, while the bacteria abundance of Bacteroides fragilis and Hungatella hathewayi were significantly lower in the Vitamin D deficiency group. The relative abundance of Bilophila wadsworthia and Adlercreutzia equolifaciens were negatively correlated with serum T-25(OH)D levels(r=-0.45, fdr=0.055, P=0.002;r=-0.44, fdr=0.055, P=0.003), and the relative abundance of Bacteroides fragilis was positively correlated with serum T-25(OH)D levels (r=0.42, fdr=0.073, P=0.004).

Vitamin D deficiency in ASD may exacerbate ASD flora disorders, and decreased serum T-25(OH)D levels may facilitate potentially harmful bacteria but inhibit probiotic colonization. This study provides partial evidence that children with ASD should be actively supplemented with vitamin D.