Researchers have noticed a link between Vitamin D and ASD for years. A new study explains how a lack of the vitamin could lead to problems in fetal and neonatal brain development, creating the symptoms of autism spectrum disorder.
Rhonda Patrick and Bruce Ames of Children's Hospital Oakland Research Institute showed that vitamin D is essential for the synthesis of serotonin in the brain. They also show that it may be important for the making the precursor to oxytocin, as well as for the formation of the oxytocin receptor and vasopressin receptors. All three of these chemicals, which are both neurotransmitters and hormones that regulate body functions, are crucial for social behavior.
What Patrick's and Ames's study adds is an explanation for just how the lack of Vitamin D "turns off" serotonin production:

Vitamin D activates the gene that makes an enzyme that converts tryptophan into serotonin in the fetal brain.
Serotonin in the fetal and neonatal brain influences the structure and wiring of the brain.
Serotonin also acts as a neurotransmitter.
In the post-natal brain, serotonin affects social behavior.

In other words, Patrick says, "In order to make the hormone, you have to make this protein first." And it's vitamin D that allows the body to make the proteins that in turn create oxytocin, vasopressin and serotonin.
Patrick thinks the lack of enough serotonin in the fetal and neonatal brain could cause it to form in a way that causes the symptoms of ASD. She says, "During early fetal development, serotonin is a brain morphogen -- it's a growth factor for the brain. It guides the structure and some of the way that the neuronal connections are made."
Even before the fetal brain begins making its own serotonin, she adds, serotonin from the mother's body enters the fetus through the placenta and guides some brain development. Therefore, a vitamin D deficiency in the mother could also cause ASD.
In 2009, Swedish researchers studying the rise in autism spectrum disorder among Somali immigrants posited that it was because the dark-skinned immigrants weren't producing enough Vitamin D when exposed to the weak northern sun. (In fact, the Somali Swedes called autism "the Swedish disease.")

Deficits in oxytocin and vasopressin have also been linked to ASD, and Patrick thinks that, if the genes to produce their precursor proteins have similar responses to Vitamin D, it's possible that these two neurochemicals also are part of the puzzle. But this paper focuses on serotonin and its precursor, the essential amino acid tryptophan.
Patrick says that it's easy to create a temporary deficit of tryptophan in humans, and studies in the lab have shown that people whose tryptophan is depleted begin to have trouble decoding people's facial expressions, a prime symptom of autism.
Meanwhile, preventing autism could be as simple as adequate vitamin D supplementation for pregnant and nursing women and making sure young children have adequate levels of vitamin D. The paper concludes, "Supplementation with vitamin D and tryptophan would be a practical and affordable solution to help prevent autism and possibly ameliorate some symptoms of the disorder."
While people over 60 are commonly tested by their doctors to make sure they have adequate levels of vitamin D, Patrick thinks this should also be standard for pregnant women. "I think it needs to be up there with folic acid in terms of prenatal care," she says.
For parents looking for help now, Patrick says, "I wouldn’t rush out and give a child high doses of tryptophan. I certainly would get the vitamin D levels tested; it's a very simple test to do."
CHORI is beginning clinical trials looking at the effects of micronutrients on diseases. Patrick also is working with organizations involved in ASD research and treatment to design clinical trials to see if vitamin D could reduce autism symptoms. Patrick and Ames will set up a website to act as a resource for parents of children with ASD. They also hope to do clinical trials. To find out whether Patrick and Ames will start testing of kids with ASD or clinical trials of the vitamin to ameliorate symptoms, keep an eye on

For details about the study, read the Science Daily article.