L-tyrosine is a non-essential amino acid, that is a precursor to the catecholamine neurotransmitters. When consumed l-tyrosine can cross the blood brain barrier, where it can be converted to adrenaline, noradrenaline and dopamine. Supplemental l-tyrosine has been shown to increase levels of these catecholamine neurotransmitters in humans, and this is of particular interest because low levels are associated with stress. L-tyrosine may therefore be a useful supplement to alleviate one of the causes of stress. L-tyrosine is present in all foods that contain protein, but evidence suggests that in its protein form it is not efficiently absorbed across the blood brain barrier, because it competes with certain other amino acids in the protein. Talking supplements of l-tyrosine is the best way to increase blood and brain levels of tyrosine, and thereby increase brain levels of catecholamines. A number of studies have investigated the effects of l-tyrosine supplements on stress in humans.
For example, in one study1, researchers investigated the effects of l-tyrosine supplements to prevent the lower negative body pressure caused when subjects had their lower extremities artificially exposed to a vacuum. Administration of 100 mg/kg of body weight l-tyrosine increased the pulse pressure of the subjects, suggesting that some of the negative effects of the treatment had been ameliorated. The subjects also exhibited auditory changes that are associated with cognitive improvements. Because the treatment the subjects were exposed to reduces pulse pressure, and this change was inhibited by administration of l-tyrosine, these results support the contention that dietary supplements of l-tyrosine are able to improve the production of catecholamines that in turn can increase blood levels of catecholamines, increasing sympathetic response. Animal experiments also support a role for l-tyrosine supplements in reducing stress in animals, research showing that this occurs through a common mechanisms in all mammals.
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