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Resurfacing tryptophan

Essential amino acid tryptophan had been one of the most popular topics of nutritional neuroscience studies of the 1980s. The scientific (and commercial) interest was directly linked to the ability of tryptophan to cross the blood-brain barrier, which separates the brain from the rest of the body, and to stimulate synthesis of an inhibitory brain neurotransmitter serotonin that is involved in etiology of sleep, stress and mood regulation. Indeed, even a short-term deficiency of dietary tryptophan substantially worsened mental health and sleep quality in both healthy and depressed people because it affected serotonin availability (www.ncbi.nlm.nih.gov/pubmed/19721848, www.ncbi.nlm.nih.gov/pubmed/15935252). On the other hand, tryptophan supplementation (at certain doses) increased subjective drowsiness, leading to better onset of sleep and decreased pain sensitivity, sometime more efficiently than analgesic drugs did. www.ncbi.nlm.nih.gov/pubmed/6473667 Importantly, unlike many hypnotics, tryptophan did not impair sensorimotor performance.

Clinical research was suddenly terminated in 1990; shortly after it was reported that a single batch of a dietary supplement containing tryptophan caused a deadly disease. Soon afterwards, it was documented that the direct cause of the disease was an impurity present in the problematic supplement. Products that contained tryptophan with sufficiently tight specifications (typically US Pharmacopeia and recently also Food Chemical Codex (FCC)) had not been linked to any problems. Consequently, tryptophan was re-approved in major markets in middle 2000s; and the scientific interest in its application has been rising again.

Scientific experiments conducted since 2005 only re-confirmed that tryptophan can improve sleep quality and mood. Elderly and middle-age groups have been especially targeted in clinical studies (www.ncbi.nlm.nih.gov/pubmed/22622709, www.ncbi.nlm.nih.gov/pubmed/25693900). When the tryptophan-containing supplements were taken 60-90 min before bedtime in middle-aged women (www.ncbi.nlm.nih.gov/pubmed/25572038), a feeling of happiness before going to bed was consistently found. Authors of the last study reported that daily consumption of a low-dose tryptophan supplement was beneficial even on cognitive functions. Taken together, clinical research of the last decade has showed again that tryptophan loading is effective for improving mood in vulnerable subjects, and improving sleep in middle-aged and elderly adults with some minor sleep disturbances.

Are there side effects from high-quality modern tryptophan supplementation? Though the literature is thin, occasional side effects, seen mainly at higher doses (70-200 mg/kg body weight), include tremor, nausea, and dizziness, and may occur when tryptophan is taken with a drug that enhances serotonin function (e.g., antidepressants). A recent toxicological study conducted in healthy females documented that tryptophan alone is safe up to 5 grams per day (www.ncbi.nlm.nih.gov/pubmed/23616514 ). The last report and absence of side-effect in controlled studies document that controlling quality is much more important than controlling maximum daily dose – an observation constantly reported for all essential and semi-essential amino acids.