Researchers discover how low vitamin D levels are linked to Autism Spectrum Disorder

OAKLAND, Calif. — A study released Wednesday by Rhonda Patrick and Bruce Ames of Children's Hospital Oakland Research Institute demonstrated the impact that vitamin D may have on social behavior associated with Autism Spectrum Disorder. 

Patrick and Ames show that serotonin, oxytocin and vasopressin, three brain hormones that affect social behavior, are all activated by vitamin D hormone. Autism, which is characterized by abnormal social behavior, has previously been linked to low levels of serotonin in the brain and to low vitamin D levels, but no mechanism has linked the two until now. 

In this study, Patrick and Ames show that vitamin D hormone activates the gene that makes the enzyme tryptophan hydroxylase 2 (TPH2), which converts the essential amino acid tryptophan, to serotonin in the brain. This suggests that adequate levels of vitamin D may be required to produce serotonin in the brain where it shapes the structure and wiring of the brain, acts as a neurotransmitter and affects social behavior. They also found evidence that the gene that makes the enzyme tryptophan hydroxylase 1 (TPH1) is inhibited by vitamin D hormone, which subsequently halts the production of serotonin in the gut and other tissues, where when found in excess, it promotes inflammation.

This mechanism explains many of the known, but previously not understood facts about autism including: 1) the "serotonin anomaly" low levels of serotonin in the brain and high levels in the blood of autistic children; 2) the preponderance of male over female autistic children: estrogen, a similar steroid hormone, also can boost the brain levels of serotonin in girls; 3) the presence of autoimmune antibodies to the fetal brain in the mothers of autistic children: vitamin D regulates the production of regulatory T-cells via repression of TPH1. The Patrick/Ames mechanism is relevant to the prevention of autism, and likely its treatment, the researchers concluded.

The study suggests dietary intervention with vitamin D, tryptophan and omega-3 fatty acids would boost brain serotonin concentrations and help prevent and possibly ameliorate some of the symptoms associated with ASD without side effects. There is little vitamin D present in food, and fortification is still inadequate as is the amount in most multivitamin and prenatal supplements. In addition, vitamin D levels should be routinely measured in everyone and should become a standard procedure in prenatal care.