Place · Level 3 · Nootropics
L-tyrosine
Last updated
In one pass Tyrosine reaches the brain through the large-neutral-amino-acid transporter (LAT1) at the blood-brain barrier. Educational content, not medical advice — consult a clinician.
Story path
Chapter 1
One door, several amino acids in line
一扇门, 好几种氨基酸在排队
Tyrosine reaches the brain through the large-neutral-amino-acid transporter (LAT1) at the blood-brain barrier. The same door also takes tryptophan, phenylalanine, and the branched-chain amino acids leucine, isoleucine and valine. They compete for seats. They do not each have a private lane.
Fernstrom 2013 writes the competition hard: raise blood tyrosine and brain tyrosine uptake rises; raise blood BCAA and both tyrosine and tryptophan uptake fall. The steps that turn tyrosine into catecholamines and tryptophan into serotonin track what got through the door.
This island is not how magical a capsule is. It is which amino acid currently occupies the door. The nervous-system island already used BCAA crowding out tryptophan for this same door. Here the tyrosine side of that line is filled in.
Fernstrom 2013 writes the competition hard: raise blood tyrosine and brain tyrosine uptake rises; raise blood BCAA and both tyrosine and tryptophan uptake fall. The steps that turn tyrosine into catecholamines and tryptophan into serotonin track what got through the door.
This island is not how magical a capsule is. It is which amino acid currently occupies the door. The nervous-system island already used BCAA crowding out tryptophan for this same door. Here the tyrosine side of that line is filled in.
Mechanism · why a protein meal barely lifts catecholamines
A protein meal raises tyrosine and its competitors together. Fernstrom's surprise sits here: meals can swing tryptophan uptake and serotonin synthesis a lot, and tyrosine uptake and catecholamine synthesis only a little — because the same protein is rich in BCAA, which occupy the door.The other direction is the one that actually changes the ratio: taking tyrosine apart from those competitors. This step is the door. It is not 'eat more meat and brain dopamine rises'.
Chapter 2
Hydroxylase is the brake
羟化酶才是刹车
Getting in is not enough. The first cut that turns tyrosine into dopamine and norepinephrine is tyrosine hydroxylase. At rest the enzyme is already near saturation: more substrate barely speeds the cut. So sitting quietly, extra tyrosine in blood often does not raise brain catecholamines.
The brake eases when the pool is being spent. Fast firing, released catecholamines, phosphorylation of the enzyme — then it becomes substrate-sensitive again, and extra tyrosine at the door can refill the gap.
The nervous-system island already wrote phenylalanine → tyrosine → DOPA, and iron as a cofactor of the hydroxylase. This scene adds one sentence: what is missing is not the everyday store. It is the minutes being spent.
The brake eases when the pool is being spent. Fast firing, released catecholamines, phosphorylation of the enzyme — then it becomes substrate-sensitive again, and extra tyrosine at the door can refill the gap.
The nervous-system island already wrote phenylalanine → tyrosine → DOPA, and iron as a cofactor of the hydroxylase. This scene adds one sentence: what is missing is not the everyday store. It is the minutes being spent.
Judgement · daily 'energy' reads the brake backwards
Shelf copy for daily energy assumes the hydroxylase is always hungry and you are always short of tyrosine. Fernstrom's competitive door plus hydroxylase saturation point the other way: extra intake at rest mostly fills a pipe that is already full.The window that can actually match is a short burst of high use. Writing the supplement as a daily stimulant sells an emergency lane as breakfast.
Chapter 3
Only when it is being spent
只有被花掉的时候才补得上
Jongkees 2015 folds the human trials into one conditional: tyrosine can hold performance under short-term stress or cognitive load, if the synthesis machinery is intact and dopamine or norepinephrine is only temporarily depleted. Using it as a treatment for clinical disorders looks limited; using it to raise exercise performance looks weak.
Read both premises. If the machinery is broken (the synthesis path itself is sick), adding substrate does not rebuild it. If nothing has been spent and the person just wants to feel sharper, there is little to refill.
This scene is not a dose table. It only draws when the door and the brake are open at the same time.
Read both premises. If the machinery is broken (the synthesis path itself is sick), adding substrate does not rebuild it. If nothing has been spent and the person just wants to feel sharper, there is little to refill.
This scene is not a dose table. It only draws when the door and the brake are open at the same time.
Limits · the lines the review itself draws
Jongkees writes the useful window as short-term stress or cognitive demand, not a long course. Whether a disease can use it depends on whether the path is short of substrate for a while or the machinery is broken. On the exercise side, too many other things sit between catecholamines and the watch, so tyrosine barely moves performance.Do not stretch 'a signal under short-term stress' into 'a daily scoop makes you smarter'.
Chapter 4
Not a daily stimulant
不是日常提神
Fold the three scenes into one drawable judgement: the door is shared, the brake is on at rest, and only the minutes being spent can use extra tyrosine at the door.
PKU is a different line: the register already holds tyrosine in phenylalanine-restricted diets. That is substrate management in a metabolic disease, not this island's stimulant pitch. Do not merge the two problems into one capsule.
The island stops here. It does not answer milligrams and it does not join the fueling-for-training path. That path leaves tyrosine out on purpose: the trunk is not a shelf.
PKU is a different line: the register already holds tyrosine in phenylalanine-restricted diets. That is substrate management in a metabolic disease, not this island's stimulant pitch. Do not merge the two problems into one capsule.
The island stops here. It does not answer milligrams and it does not join the fueling-for-training path. That path leaves tyrosine out on purpose: the trunk is not a shelf.
Judgement · do not merge it with the next amino acid
L-theanine also uses LAT1, but it is there to tap glutamate noise and alpha waves, not to refill catecholamines. This island only covers the stretch in front of the hydroxylase. Two doors that look alike feed different enzymes.References · 2
- Fernstrom, J. D. (2013). Large neutral amino acids: dietary effects on brain neurochemistry and function. Amino Acids, 45(3), 419-430. Competitive LNAA transporter at the blood-brain barrier: raising blood tyrosine raises brain tyrosine uptake; raising BCAA lowers tyrosine (and tryptophan) uptake. Catecholamine synthesis tracks the tyrosine change. Protein meals move tryptophan/serotonin more than tyrosine/catecholamines. 10.1007/s00726-012-1330-y
- Jongkees, B. J., Hommel, B., Kuhn, S., & Colzato, L. S. (2015). Effect of tyrosine supplementation on clinical and healthy populations under stress or cognitive demands — a review. Journal of Psychiatric Research, 70, 50-57. Tyrosine can enhance cognition in short-term stressful or cognitively demanding situations, when dopamine/norepinephrine are temporarily depleted and the synthesis machinery is intact. Limited for treating clinical disorders; little for physical exercise. 10.1016/j.jpsychires.2015.08.014