The lack of social behavior that characterizes ASD is controlled by three brain hormones, serotonin, oxytocin and vassopressin, that are all activated by vitamin D. There have been many unknown facts regarding 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, can also boost the brain levels of serotonin in girls; 3) the presence of autoimmune antibodies to the fetal brain in the mothers of autistic children.
The findings of this study revealed that vitamin D activates the gene that produces the enzyme tryptophan hydroxylase 2 (TPH2), that converts the essential amino acid tryptophan, to serotonin in the brain. Sufficient levels of vitamin D may be required to produce serotonin in the brain where it directly affects the structure and wiring of the brain, acts as a neurotransmitter, and impacts on social behavior.
Vitamin D acts as an inhibitor of the gene that produces the enzyme tryptophan hydroxylase 1 (TPH1); subsequently halting the production of serotonin in the gut and other tissues. When found in excess it promotes inflammation. Vitamin D regulates the production of regulatory T-cells via repression of TPH1 (tryptophan hydroxylase 1).
The current daily recommended guidelines for adequate vitamin D levels are concentrations above 30 ng/ml. The most recent National Health and Examination survey reveals that more than 70% of U.S. population does not meet this requirement and that adequate vitamin D levels have plummeted over the last couple of decades. This drop in adequate levels of vitamin D in the US is concurrent with the pervasive rise in autism rates.
The study recommends that measuring vitamin D levels should be included as routine prenatal care. Dietary intervention with vitamin D, tryptophan and omega 3 fatty acids would boost brain serotonin concentrations and help prevent and possibly mitigate some of the symptoms associated with ASD without side effects.
R. P. Patrick, B. N. Ames. Vitamin D hormone regulates serotonin synthesis. Part 1: relevance for autism. The FASEB Journal, 2014; DOI: 10.1096/fj.13-246546