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L-Tyrosine is an important precursor to the brain neurotransmitters dopamine, epinephrine, and norepinephrine. If intake from dietary sources is insufficient, phenylalanine can be used for tyrosine biosynthesis with the help of the necessary cofactors iron, vitamin C, and niacin. The thyroid hormones triiodothyronine (T3) and thyroxine (T4) are also derived from tyrosine.
As a component of protein, tyrosine content varies greatly in foods. In general, meats contain higher concentrations than vegetables or grains, with wheat germ being one exception. As an individual amino acid, tyrosine possesses poor water solubility. This is the primary reason why some parenteral nutrition products use N-acetyl-L-tyrosine (NAT) instead of L-tyrosine itself.
Despite the presence of active transport mechanisms for amino acids in intestinal enterocytes, the poor solubility of L-tyrosine may hinder its bioavailability. Experientially, users familiar with taking L-tyrosine often report heightened effects when taking a similar quantity of NAT. It has also been reported that, as an addition to drinks or shakes, NAT offers a more palatable taste than tyrosine.
As with the intestines, there are active transporters that allow tyrosine to cross the blood-brain barrier. However, these transport mechanisms are not specific to tyrosine and ferry other similar amino acids into the brain as well. Once in the brain, tyrosine can be used as a feedstock for the neurotransmitters dopamine, epinephrine, and norepinephrine.
With age, however, brain dopamine production often declines. In the basal ganglia, dopamine deficiency can lead to motor function decline related to coordination, reflexes, and gait. It is not entirely clear why this occurs, but one hypothesis posits that decreased levels of antioxidant enzymes, allow byproduct hydrogen peroxide accumulation around dopamine-producing cells, leading to damage.
Aside from assisting in coordination and tissue repair (by aiding growth hormone release), dopamine promotes the pleasure response to activities like eating and sex. One theory suggests that some cases of overeating may be due to poor dopamine production and/or regulation in the brain. NAT may provide nutritional support in the brains response to falling dopamine levels.
Mood: Food Matters
Sadness and discouragement are natural responses to disappointment or loss. Nevertheless, in our modern society, mood is sometimes off-kilter due to diet and lifestyle imbalances. In fact, it is not uncommon for people who report frequent cases of the blues to have diets deficient in vitamins, minerals, and protein ,but high in refined carbohydrates.
Inadequate protein intake, excessive stimulant intake or chronic stress can not only lead to reduced levels of dietary tyrosine but also to depressed levels of tyrosine-dependent hormones and neurotransmitters. In some cases a vicious cycle between poor diet and poor mood occurs. Biochemically, those with low spirits may have elevated levels of the norepinephrine metabolite, 3-methyl4-hydroxy-phenylglycol (MHPG). In some cases elevated levels of this biomarker indicate depressed tyrosine metabolism.
As a precursor for excitatory neurotransmitters, tyrosine is an important reserve in the bodys response to stressful conditions. In studies performed at MIT, animals given extra tyrosine were better able to control stress and avoid depression; human trials with soldiers undergoing intense physical training bolstered these results. Several studies have found tyrosine useful during conditions of stress, cold, fatigue, prolonged work, and sleep deprivation by helping to support balanced stress hormone levels, proper metabolism, and robust cognitive performance under adverse conditions. Supplemental NAT may help promote tyrosine balance.
Tyrosine plays an important role in cell signaling by regulating many cellular processes via tyrosine kinase receptors (including sensitivity to insulin). Tyrosine is also the precursor to the pigment melanin, which is used by the body in UV radiation protection. There is also some recent evidence suggesting that melanin acts as a powerful chelating agent in the body, as it helps to sequester toxic heavy metals. Tyrosine deficiency may cause edema, weakness, impaired liver function and loss of muscle or other tissues. Low protein diets may produce marginal deficiency states.
N-Acetyl Tyrosine is an acetylated derivative of the amino acid L-tyrosine. Ordinary L-tyrosine is less stable and also less soluble in water, which may result in reduced bioavailability. Acetylation enhances the solubility and stability of certain amino acids. Jarrow Formulas N-Acetyl Tyrosine also contains vitamin B6 to promote the conversion of tyrosine to neurotransmitters and hormones in the body.
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