Tyrosine for Mitigating Stress and Enhancing Performance in Healthy Adult Humans, a Rapid Evidence Assessment of the Literature

Background: Tyrosine, a precursor of catecholamine neurotransmitters, may help alleviate physical/cognitive performance decrements in humans under conditions of high physical/psychological stress. Objective: Determine whether supplemental tyrosine mitigates stress-induced decrements in cognitive and/or physical performance in healthy individuals using Samueli Institute's Rapid Evidence Assessment of the Literature methodology. Methods: Key databases (PubMed/MEDLINE, CINAHL, Embase, PsycInfo, and Agricola) were searched for randomized controlled trials from inception to October 2012. Scottish Intercollegiate Guidelines 50 criteria and Grading of Recommendation Assessment, Development, and Evaluation framework were used to assess the quality of individual studies and the overall literature pool, respectively. Controlled clinical trials were included later in the overall methodology. Results: 10 randomized controlled trials and 4 controlled clinical trials met our inclusion criteria. On the basis of the available evidence, no recommendation could be made for the effect of tyrosine on physical performance under stressful physical conditions. However, a weak recommendation in favor of tyrosine was made for cognitive stress as all studies showed a positive effect. Conclusions: This review indicates that the available evidence is insufficient to make confident recommendations on the effectiveness of tyrosine for mitigating stress effects on physical/cognitive performance. However, tyrosine may benefit cognitive performance and is worthy of further study.