Effect of L-tryptophan Supplementation on Mood, Cognitive Function and Sleep in Relation to Dietary Protein Intake. A randomized double blinded placebo control study.

Abstract

Background: The essential amino acid L-tryptophan is the sole precursor molecule for the monoamine neurotransmitter serotonin. Due to the role serotonin plays in regulating mood, cognition and sleep dietary supplementation of L-tryptophan has been explored in scientific literature. Evidence suggests that it may have a beneficial role in conditions were serotonin dysfunction Is present, such as major depressive disorder however evidence is for its use in healthy individuals has shown mixed results. This may be due to the fact that L-tryptophan transport across the blood brain barrier is dependent on a shared carrier with other large neutral amino acids. Objectives: The aim of the study was to assess how L-tryptophan supplementation in healthy individuals at a practical dose would affect mood, sleep quality and cognitive function. The secondary objective was to reveal if there was any correlation with dietary intake and any significant changes to the primary outcome measures. Method: This study preformed a randomised double blind placebo controlled study in healthy student volunteers (n=10). Cycles of 800mg tryptophan and 2g placebo were administered for 6 days in total, with a washout of 2 days in between each cycle. At the beginning of the study and following each intervention week, participants were subjected to a series of tests to assess cognition, mood and sleep quality. Stoop and reverse digit span tests were used to asses cognition, a Profile of State Questionnaire was use to assess mood, and the Pittsburgh Sleep Quality Index was used to determine quality of sleep. A 4 day diet diary was used to analyse the diet of the participants. Analysis of variance tests with pos-hoc analysis was used to find any changes in these measurements at baseline, following placebo and following tryptophan. A Pearson's correlation was used to test for any correlations between significant findings and protein intake. Results: Results found that there was a significant change (p≤0.05) in POMS scores for anger when baseline measurements were compared to tryptophan and placebo results. A Significant result was also found in reverse digit span test (p≤0.05) where placebo was found to decrease response time when compared to baseline. A Pearson's correlation was only found between protein intake and anger scores at baseline. Conclusion: The results obtained did not suggest tryptophan produces any significant improvement in mood, sleep or cognition when compared to a placebo. This could be due to limitations in the design of the study such as, low sample size and insufficient follow up in dietary analysis. It could also be as a result of inaccuracies in the personally subjective nature of the tests used. Future studies should therefore look to improve study design, and measure both subjective measurements for mood and cognition, along with biomarkers which show the underlying effects supplementation mayor may not have within the brain Key Words: L-tryptophan, Supplementation, Cognition, Mood, Sleep, Diet,