Solving Autism: Vitamin D and Serotonin Synthesis


Professor Bruce Ames is arguably one of the greatest thinkers and innovators in nutritional medicine of our age, so his most recent contribution concerning Vitamin D, Serotonin Synthesis and Autism will undoubtedly make big waves in the world of autism research, clinical nutrition, and beyond.

A recent groundbreaking scientific publication helps solve a number of mysteries that have faced autism researchers over the years. By exploring new nutrient-gene interactions, Professor Ames and coauthor Rhonda Patrick reveal novel biological mechanisms underlying autism that will undoubtedly help pave the way for new preventive approaches and better treatment.

Bruce Ames is a professor of Biochemistry and Molecular Biology at the University of California, Berkeley.  Throughout his long and distinguished career (he is an active professor at age 85) he has received numerous prestigious awards and was described by the founder of functional medicine; Jeff Bland PhD, as “the Linus Pauling of our time.” Notably, he has been instrumental in pioneering, and substantiating through meticulous experimental work, some of the greatest paradigm shifts in nutritional wisdom in recent times. So when Professor Ames publishes new scientific work it pays to take heed, and his most recent publication is one of his most important.

In the words of Ames and Patrick, the new publication “presents a unifying mechanistic hypothesis that links vitamin D and serotonin concentrations to these disparate observations and to the increased autism incidence.” Using the University of California–Santa Cruz’s genome database, they identified genes that are abnormally expressed in autism and then went on to show, for the first time, that these genes are responsive to regulation by vitamin D. This then helped them solve some important problems in autism.

More specifically, what they discovered was that vitamin D activates the gene for tryptophan hydroxylase (TPH), the rate-limiting enzyme in serotonin synthesis, in the brain and inhibits the gene for TPH in tissues outside the blood-brain barrier. Low vitamin D, a frequently reported problem in autism, has been proposed to play an important role in the development of autism but it has been unclear why, and there have been confusing findings related to disordered serotonin levels in people with autism, suggesting this neurotransmitter plays an important role as well. Remarkably, what this new discovery does is help to fit pieces of the puzzle together and solve some major problems in our understanding of autism. Here are 5 of the major breakthroughs:

1.      Upside-down serotonin.

One of the confusing observations in autism is that brain levels of serotonin are typically low, yet blood levels outside the brain are high. This new research suggests that adequate vitamin D increases serotonin synthesis in the brain, and decreases it in the periphery via differential regulation of TPH. So low vitamin D status helps to explain why children with autism tend to have high levels of serotonin in their blood but unusually low brain serotonin. Disordered serotonin levels are thought to play a role in abnormal brain development and behavioral symptoms.

2.      Boyish bias  

There is a preponderance of autism in boys, who are much more likely to develop the disorder than girls. Importantly, the female sex hormone estrogen is known to increase the expression of TPH in the brain so it may be that the female brain is protected against the adverse effects of vitamin D deficiency on serotonin synthesis and the risk of developing autism. In other words, boys brains are more sensitive to low vitamin D and thus at greater risk.

3.      Maternal attack

“Maternal autoimmunity has been strongly associated with the development of autism during pregnancy, although no satisfactory explanation of this phenomenon has been put forward” point out Ames and Patrick. Their discovery also helps explain this association.  A protein called kynurenine plays an important role in preventing autoimmune responses to the fetus during pregnancy by generating regulatory T cells in the placenta.  Well, it turns out that the amino acid required for serotonin synthesis, tryptophan, is also a precursor to kynurenine. So low vitamin D and resultant increased expression of TPH may shunt tryptophan away from the kynurenine pathway and decrease placental production of kynurenine. Low kynurenine means low regulatory T cells and a higher risk of developing autoimmunity.

4.        Inflamed gut

Chronic gastrointestinal (GI) inflammation and digestive disorders are characteristic of autism. In the gut excess serotonin can result in immunological changes and increased gastrointestinal inflammation. Ames and Patrick propose that the “gastrointestinal inflammation observed in individuals with autism may be a direct result of elevated serotonin in the GI tract due to increased TPH expression as a consequence low vitamin D hormone levels.” And they go on to propose, “that raising vitamin D concentrations should help lower GI inflammation by decreasing serotonin concentrations in the GI cells through transcriptional repression of TPH.” The increase production of serotonin production in the gut may also be at the expense of production in the brain.

5.       Social connection

Low vitamin D may directly explain social deficits associated with the autism. Ames and Patrick examined the genes responsible for the production of the neuropeptide hormone oxytocin. Oxytocin is known to play an important role in social behavior, low levels have been associated with autism, and administration of oxytocin to adults with autism has been has been shown to improve measures of socialization. They discovered that the vitamin D receptor is an activator of the oxytocin gene, suggesting that low vitamin D would result in low oxytocin production.

New understanding, new hope.

As you can see, this remarkable work takes us several strides forward in our understanding of the mechanisms underlying the biology of autism, but what about the practical implications? What makes this publication exceptional is that beyond the exploration of molecular pathways and nutrient-gene interactions, it concludes with a detailed discussion of therapeutic implications.

Firstly Ames and Patrick discus the implications for autism prevention, and the most obvious is of course treatment of vitamin D deficiency; “The vitamin D-dependent regulatory mechanisms of serotonin synthesis and their relationship to the underlying causes of autistic spectrum disorders (ASD) suggest that risk of ASD may be decreased by a practical and affordable solution: adequate vitamin D supplementation during pregnancy and early childhood.”

But perhaps most interesting is their discussion around implications for treatment. “Understanding the mechanism by which vitamin D levels regulate serotonin synthesis in different tissues gives some insight into therapeutic treatment, with the goal of improving a wide-range of social behaviors,” they state. Some of their key implications for therapeutic intervention are:

  • – L-Tryptophan supplementation – which may help increase brain serotonin and reduce social anxiety without negative side effects.
  • – Avoid using 5-hydroxytryptophan (5-HTP) – as it may be rapidly convert to serotonin in the gut and increase gastrointestinal inflammation while limiting delivery of tryptophan to the brain.
  • – Administer L-Tryptophan with Vitamin D – as vitamin D will enhance serotonin synthesis in the brain and limit its production in the gut. Vitamin D may also improve oxytocin production.
  • – Avoid serotonin reuptake inhibitors (SSRIs) – they have been use in autism but with mixed results, likely because their effect on serotonin is unclear. L-Tryptophan and Vitamin D would have a more direct effect on serotonin.
  • – Consider vitamin B6, folate, iron and omega-3 fatty acids – they are co-factors in serotonin synthesis and may help improve symptoms.

Intriguingly, this seminal publication is Part 1 of a series. I am very excited to see where the work of Professor Ames and Rhonda Patrick take us next.


Benjamin Brown, ND. Ben is a naturopath, speaker, and science writer. Visit



Patrick RP, Ames BN. Vitamin D hormone regulates serotonin synthesis. Part 1:  relevance for autism. FASEB J. 2014 Feb 20. [Epub ahead of print]


3 Comments On “Solving Autism: Vitamin D and Serotonin Synthesis”

  1. What doses of L-tryptophan and Vitamin D does Dr Ames suggest?

  2. Would we then want to look at Kynurenate & Quinolinate prior to administration of Tryptophan to rule out inflammation, excitotoxic, and immune responses?

  3. Excellent article, good questions. This is of personal interest to me in terms of correctly addressing the source(s) of our family’s auto-immune, metabolic and psychiatric disorders, rather than accepting the ineffective treatment of chronic symptoms (which seem only to evolve into additional, yet connected, medical problems).

    I look forward to reading further, with kind thanks,

    Karenannie (anon)

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