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A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance: Part 38
  1. N Cermak1,
  2. T Yamamoto2,
  3. R Meeusen3,
  4. L M Burke4,
  5. S J Stear5,
  6. L M Castell6
  1. 1Department of Human Movement Sciences, Maastricht University Medical Centre, Maastricht, The Netherlands
  2. 2Laboratory of Neurophysiology, Department of Psychology, Tezukayama University, Nara, Japan
  3. 3Department of Human Physiology & Sportsmedicine, Vrije Universiteit Brussel, Brussels, Belgium
  4. 4Australian Institute of Sport, Canberra, Australia
  5. 5Performance Influencers Limited, London, UK
  6. 6Green Templeton College, University of Oxford, Oxford, UK
  1. Correspondence to L M Castell, Green Templeton College, University of Oxford, Oxford OX2 6HG, UK; lindy.castell{at}

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Introductory remarks

Three amino acids are discussed in Part 38, which begins with an essential amino acid, threonine. In animal studies it is important for maintaining gut function, and also has a role in immune function. The amino acid tryptophan is a precursor of serotonin. It was first shown to be instrumental in promoting fatigue in rats, and this has since been confirmed in humans. It has mainly come to prominence in sports studies because of attempts to counteract its fatiguing effects by the use of branched chain amino acids (BCAA). Recently there has been some interest in the soporific effects of tryptophan, which were first observed in the 1960s. The third amino acid discussed is tyrosine: its increase across the blood–brain barrier can promote an increase in dopamine and norepinephrine.


N Cermak

Threonine is one of the nine essential amino acids required by humans. As such, threonine cannot be synthesised endogenously, and thus threonine must be obtained through diet or nutritional supplementation. Foods high in threonine include cottage cheese, poultry, fish, meat, lentils and sesame seeds. In animals, threonine is a primary component of intestinal mucin protein and plasma γ-globulin required for maintaining gut function.1 Threonine supplementation in chickens, pigs and mice has been shown to elevate serum antibodies against various viruses, providing support for a role of dietary threonine in modulating immune function.1 ,2 In rats, threonine deficiency has been found to depress the synthetic rate of phospholipid and nucleoprotein …

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  • Competing interests None.

  • Provenance and peer review Commissioned; not externally peer reviewed.

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