Researchers have reported elevated and unusually broad vitamin B6 (RBC and plasma) concentrations in autistic children. Autistic children from the US had vitamin B6 concentrations [measured as RBC pyridoxal 5-phosphate (P5P) and total vitamin B6 in plasma] >2 times SDs of their non-sibling neurotypical controls, and neither group was taking vitamin/mineral supplements. These findings indicate that children with autism may have a low activity of pyridoxal kinase that converts pyridoxal and pyridoxine into the active form P5P. This would ultimately result in high amounts of pyridoxal and, therefore, total vitamin B6, as well as low amounts of P5P, which is the active cofactor for several enzymatic reactions, including the formation of many key neurotransmitters. Broad distribution of RBC P5P also suggests that there is a subset of children who need more vitamin B6 and a subset who have high concentrations of B6. This explains the benefits of high-dose B6 supplementation in individuals with autism with low RBC P5P. Inadequate intake of B6 by autistic children in China was observed, and researchers suggested that supplementation with B6 can have positive benefits for behavior because it is required for brain development and function.
Sabhana Ranjan and Jennifer Nasser. Nutritional Status of Individuals with Autism Spectrum Disorders; Do We Know Enough? Advances in Nutrition. July 2015 vol. 6: 397-407, 2015