Effects of l-Tyrosine on working memory and inhibitory control are determined by DRD2 genotypes: A randomized controlled trial, Colzato LS, Steenbergen L, Sellaro R, Stock AK, Arning L, Beste C, Cortex. 2016 Sep;82:217-224. doi: 10.1016/j.cortex.2016.06.010. Epub 2016 Jun 23

The amino acid L-tyrosine is a precursor for dopamine production in the brain. Dopamine has an important role in improving cognitive ability, especially under stress. Prolonged stress reduces brain dopamine stores, lowering dopamine and noradrenaline and thereby impairing memory, concentration and cognition.

Tyrosine is converted to dopamine in the brain. When dopamine reaches the required level, its production is reduced by inhibiting tyrosine hydroxylase. Studies found that, even when brain dopamine is not deficient, tyrosine supplementation improved stress-induced working memory and multitasking.

Researchers found that dopamine affects people differently because of variation in C957T gene expression, which changes the activity of D2 dopamine receptors.

Researchers from Norway, Germany and the Czech Republic examined L-tyrosine supplementation’s effect on mental function in healthy students.

A randomized, double-blind, placebo-controlled study published in Cortex in 2016 examined mental function in 166 healthy students divided into two groups: 85 received 2 grams of tyrosine daily, and 81 received daily placebo.

Participants completed computerized N-back tasks assessing task performance, with three tests of memory and concentration.

Blood tests examined genetic expressions affecting brain dopamine metabolism:

  • T/T homozygotes: genetic potential for low brain dopamine (19 in the treatment group, 22 controls).
  • C/C homozygotes: genetic potential for high brain dopamine (22 treatment, 26 controls).
  • C/T heterozygotes: genetic potential for balanced dopamine (44 treatment, 35 controls).

The aim was to determine whether tyrosine could overcome C957T expression causing impaired dopamine metabolism.

First, participants performed a 20-minute N-back task. They then took tyrosine or placebo and, one hour later, completed two further N-back tests.

Study results:

In T/T homozygotes with genetic potential for low dopamine and C/C homozygotes with potential for high dopamine, tyrosine improved N-back results and completion time compared with controls.

In C/T heterozygotes with potential for balanced dopamine, supplementation produced no statistically significant changes in test results.

Researchers’ conclusion:

L-tyrosine supplementation benefits and improves mental and cognitive performance, concentration, memory and multitasking.

In participants with impaired brain dopamine metabolism, supplementation did not cause above-normal brain dopamine levels.

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