Health Benefits Of Tryptophan

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Among the amino acids that should never be left out in your “to-have” diet list is tryptophan – and for very logical reasons. Tryptophan is an essential amino acid responsible for a wide range of metabolic functions, primarily as the precursor of serotonin (a neurotransmitter), melatonin (a neurohormone), and niacin (vitamin B3). However, the human body cannot naturally produce or synthesize it, making it an indispensable component in the human diet. Plus it carries with it a record of having the overall lowest concentration in the body ^[1], although this somehow poses not much of a concern since we only require small amounts of tryptophan on a daily basis for nutrition (3.5 to 6.0 mg/kg of body weight per day) and plentiful amounts of this amino acid can be readily obtained through a variety of food sources such as turkey, pork loin, egg white, chicken, winged beans, soybeans, seaweeds, cheese (especially mozzarella and cheddar), and pumpkin seeds. [2]

Tryptophan and Its Functions

Over the past decades since its discovery by Hopkins and Cole in 1901, tryptophan has progressively received much scientific, medical, and research attention because of one major thing: it is the sole metabolic precursor of serotonin, the neurotransmitter that maintains mood balance and whose deficiency results in depression. Additionally, an increase in the levels of other neurotransmitters and compounds found in the central nervous system such as dopamine and norepinephrine has been observed following oral tryptophan intake. Tryptophan’s involvement in serotonin synthesis in the brain translates to its association with mood, behavior, and cognition. Moreover, several clinical trials have evidenced the efficacy of tryptophan for the treatment and management of psychiatric disorders, especially when administered in combination with other therapeutic agents. Insufficient scientific data however exist regarding the possible role of tryptophan in the modulation of the endocrine system. [1]

Tryptophan, Mood and Cognition Disorders, and Autism

Around 1% of the tryptophan we consume from diets is converted into serotonin in the brain, but despite such percentage, serotonin synthesis persists to be one the most vital tryptophan pathways. Depletion of tryptophan, as some studies suggest, leads to mood-lowering effects and influences a range of cognitive processes, with impairments in learning and memory skills being observed in individuals following tryptophan depletion. [3] Shaw, Turner, and Del Mar (2001) reviewed randomized trials on 5-hydroxytryptophan (5-HTP) and tryptophan used as treatment for patients with unipolar depression and dysthymia and accumulated evidence that suggests that these substances were better than placebo at alleviating depression. [4]

A double-blind, placebo-controlled, randomized study from Connecticut Mental Health Center, New Haven, USA, explored the behavioral and biochemical responses to short-term tryptophan depletion of adult patients with autistic disorder and reported a “significant global worsening of behavioral symptoms” in majority of the autistic individuals upon depletion of tryptophan. Furthermore, tryptophan depletion led to an increase in the manifestation of behaviors such as whirling, flapping, and pacing and in self-reports of being less calm and more anxious among patients. [5]

Tryptophan and Sleep Disorders

As mentioned earlier, tryptophan functions as a biochemical precursor of serotonin, which itself can be converted into melatonin, the neurohormone responsible for the regulation of the daily night-day cycle. Various studies have investigated the effect of tryptophan on sleep, sleepiness, and sleep disorders. When taken in doses of 1 g or greater, L-tryptophan has been reported to increase sleepiness (subjectively reported) and produce a decrease in the time taken to fall asleep (sleep latency), benefitting subjects suffering from mild insomnia and individuals who take longer than normal to fall asleep. [6] In another study, L-tryptophan in doses between 1 to 15 grams was found effective in decreasing the time taken to fall asleep on the first night of administration to younger situational insomniacs. It was required to administer L-tryptophan repeatedly at low doses to produce hypnotic effects among chronic sleep-onset insomnia sufferers or those with more severe insomnia characterized by difficulty both in falling asleep and staying asleep. [7]

Tryptophan and Seasonal Affective Disorder

Seasonal affective disorder is a type of depression with seasonal pattern, occurring each year at the same time; it tends to commence in fall and worsens during the winter. Because serotonergic dysregulation has been related to seasonal affective disorder, tryptophan treatment is currently being studied as a possible management strategy and has been found to be as effective as light therapy. An open-label study from the University of British Columbia, Vancouver, demonstrated the L-tryptophan’s efficiency for patients with seasonal affective disorder manifesting poor response to bright light therapy. In this study, the addition of L-tryptophan to light therapy resulted in a reduction of mean depression scores and good clinical responses. [8]

Tryptophan, Niacin, and Coenzymes

Tryptophan can serve as a substrate for the synthesis of niacin or vitamin B3 via the kynurenine and quinolinic acid pathway and of nicotinamide adenine dinucleotide (NAD) and NAD phosphate (NADP), which are involved in electron transfer reactions in cells. [3]