Vitamin D may impact social behavior associated with Autism Spectrum Disorder (ASD), according to researchers from the Children’s Hospital Oakland Research Institute (CHORI), Rhonda Patrick, PhD, and Bruce Ames, PhD.

Research showed 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, Dr. Patrick and Dr. Ames demonstrated that vitamin D hormone activates the gene that makes the enzyme tryptophan hydroxylase 2 (TPH2), which converts the essential amino acid tryptophan into 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. Researchers also found evidence 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 promotes inflammation.

This mechanism may explain many of the known, but previously not understood, facts about autism including:
• The “serotonin anomaly”: low levels of serotonin in the brain and high levels in the blood of autistic children;
• The preponderance of male over female autistic children: estrogen, a similar steroid hormone, can also boost the brain levels of serotonin in girls;
• 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 current guidelines for adequate vitamin D levels are concentrations above 30 ng/ml. Most Americans’ vitamin D is made in the skin from exposure to UVB radiation; however, melanin pigment and sunscreen inhibit this action. This is an important cause of the well-known widespread vitamin D deficiency among dark-pigmented Americans, particularly those living in Northern latitudes. The most recent National Health and Examination Survey reported that more than 70% of the U.S. population does not meet this requirement and that adequate vitamin D levels have plummeted over the last couple of decades. This precipitous drop in adequate levels of vitamin D in the U.S. is concurrent with the rise in autism rates.

The study suggested 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. According to the report, there is little vitamin D present in food and fortification is still inadequate, as is the amount in most multivitamin and prenatal supplements. Researchers suggested that vitamin D supplements are inexpensive and offer a simple solution to raise vitamin D levels to an adequate status. In addition, vitamin D levels should be routinely measured in everyone and should become a standard procedure in prenatal care.