Is there a link between vitamin D deficiency and autism?

Recent studies show a possible relation betwen too little vitamin D and the risk of developing autism. It is also alarming that many children are born with too little vitamin D or develop a deficiency later in life, as vitamin D controls numerous processes in the human brain.

There may be a link between the increasing occurrence of vitamin D deficiency and the growing rate of autism. This is supported by several studies that are carried out by the two PH.D. researchers, Rhonda Patrick and Bruce Ames, at Children's Hospital Oakland Research Institute (CHORI). Vitamin D plays an essential role in many brain functions and should actually be termed a steroid hormone. This class of hormones also includes sex hormones and stress hormones.
In its role as a steroid hormone, vitamin D is believed to control more than a thousand physiological processes in the body, and it also controls 5-10 per cent of our genes.

Vitamin D regulates serotonin

Autism, which is characterized by serious disturbances in behavior, communication and social interaction, used to be linked to low serotonin levels in the brain. It was not until recently that the mechanisms were addressed more specifically.
Researchers have found that vitamin D controls a gene that codes an enzyme called tryptophan hydroxylase, or TPH.
TPH is responsible for converting the amino acid tryptophan into serotonin. Serotonin is primarily known as a neurotransmitter that influences our mood. In fact, anti-depressive medicine works by regulating serotonin levels in the brain.
But serotonin has many other functions in the brain and the rest of the body.
In addition, the body harbors two different genes for tryptophan hydroxylase. The gene in the brain is named TPH2. In the intestines it is named TPH1.

Separate serotonin systems in the brain and intestines

TPH1 converts tryptophan into serotonin in the intestines. Contrary to popular belief, however, this type of serotonin is unable to cross the blood-brain barrier. Although 90 per cent of the body's serotonin production takes place in the intestines, it has no influence on our brain as such. The two serotonin systems work independently of each other, but it is still important for serotonin levels in both systems to be optimal.

Too much serotonin in the intestines causes inflammation

According to Patrick and Ames (see above), serotonin in the intestines works by making blood platelets stick together (aggregate), which causes the blood to coagulate. This is necessary in order to prevent bleeding in the case of lesions. On the other hand, serotonin works like a two-edged sword, in that too much serotonin in the intestines may cause local inflammation through an activation of white blood cells (T cells) and pro-inflammatory cytokines. Studies have demonstrated how one can stop intestinal inflammation in mice by inhibiting their serotonin production.
It also turns out that the majority of children with autism not only have dysfunctions in the brain but even inflammation in the intestinal system as a consequence of the derailed serotonin levels.

Vitamin D regulates serotonin in the intestines and the brain

Autism is often associated with elevated serotonin levels in the intestines and too low serotonin levels in the brain.
The above mentioned studies revealed that vitamin D is able to inhibit TPH1, thereby controlling inflammation in the intestinal system caused by elevated serotonin levels.
Similarly, vitamin D increases TPH2, thereby increasing the serotonin production in the brain.
An independent group of researchers from the University of Arizona has confirmed that vitamin D activates the TPH2 gene in different nerve cells.

Serotonin's role in the development of the brain

During pregnancy, serotonin plays an important role in fetal brain development. Roughly speaking, serotonin determines the function and placement of different neuron types. With too little serotonin, the brain's structure and functions are affected.
According to Patrick, studies of mice show that lack of serotonin leads to autistic traits. She has also seen how the human fetus is entirely dependent on the vitamin D status of the mother. During pregnancy, vitamin D is transferred from the mother via the placenta. Afterwards, vitamin D crosses the blood-brain barrier of the fetus and activates the TPH2 gene, whereby tryptophan is converted into serotonin.
It may therefore affect the fetal brain development if the mother lacks vitamin D. In a more recent article from 2015, Patrick and Ames look closer at how both vitamin D and the omega-3 fatty acids, EPA and DHA, control the body's serotonin production, and how deficiencies may affect the risk of developing ADHD, bipolar disorder, and schizophrenia.

Pregnant women and neonates lack vitamin D

A newer study shows that more than half the babies born in Denmark have too little vitamin D. The study was carried out on 2,500 mothers and their offspring. Because the mothers were vitamin D deficient during their pregnancy, they have not been able to ensure an adequate supply of the nutrient to their babies. It is commonly known that vitamin D is necessary for normal bone formation and development in children. However, the brain, immune system, and intestinal system also depend on this vitamin - throughout life.

If you are pregnant, make sure to get enough vitamin D

Women who plan to become pregnant, and those who are already pregnant, are advised to have their vitamin D status established with a blood test. Also, they should take a vitamin D supplement throughout the winter period, if they want to be sure to have optimal vitamin D levels. As the diet only contributes with minimal amounts of the nutrient, it is even important to expose yourself to sufficient amounts of sunshine (but without getting burned).

Vitamin D, supplements, and absorption

Vitamin D is fat-soluble, which means we benefit the most from taking supplements of vitamin D dissolved in oil. It is safe to take high-dosed supplements with 38 micrograms of vitamin D in small gelatin capsules.

References:

R.P. Patrick, B.N. Ames. Vitamin D hormones regulates serotonin synthesis. The FASEB Journal 2014

Science News. Causal link found between vitamin D, serotonin synthesis and autism in new study. Science Daily. 2014

Rhonda P. Patrick and Bruce Ames. Vitamin D and the omega-3 fatty acids control serotonin synthesis and action, part 2: relevance for ADHD, bipolar disorder, schizophrenia, and impulsive behavior. The FASEB Journal 2015.