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Tyrosine

Tyrosine is an amino acid found in meat proteins. Your body uses it to help the brain and nervous system function. Based on this fact, tyrosine has been proposed as a treatment for various conditions in which mental function is impaired or slowed down, such as fatigue and depression. It has also been tried for attention deficit disorder (ADD).

Sources

Your body makes tyrosine from another common amino acid, phenylalanine, so deficiencies are rare; however, they can occur in certain forms of severe kidney disease as well as in phenylketonuria (PKU), a metabolic disorder that requires complete avoidance of phenylalanine.

Good sources of tyrosine include dairy products, meats, fish, and beans.

Therapeutic Dosages

The typical therapeutic dosage of tyrosine used in studies ranges from 7 to 30 g daily.

Therapeutic Uses

According to very preliminary evidence, tyrosine supplements may help fight fatigue and improve memory and mental function in people who are deprived of sleep or exposed to other forms of stress.1,10 Based on these findings, it can be inferred that tyrosine might enhance alertness in people suffering from jet lag, but this has not been studied directly.

Tyrosine may also provide some temporary benefit for attention deficit disorder, but the benefits appear to wear off in a couple of weeks.2,3,4 Tyrosine is said to work better for this purpose when it is combined in an "amino acid cocktail" along with gamma-aminobutyric acid (GABA), phenylalanine, and glutamine; however, there is no scientific evidence to support this use.

Although one extremely tiny study found tyrosine helpful for depression,5 a larger study found no evidence of benefit.6

Tyrosine has also been suggested for enhancing sports performance. However, in a double-blind study of twenty men, one-time use of tyrosine at a dose 150 mg per kilogram body weight failed to improve any measurement of muscular performance.

What Is the Scientific Evidence for Tyrosine?

Sleep Deprivation

A double-blind, placebo-controlled study that enrolled 20 U.S. Marines suggests that tyrosine can improve mental alertness during periods of sleep deprivation.7 In this study, the participants were deprived of sleep for a night and then tested frequently for their alertness throughout the day as they worked. Compared to placebo, 10 to 15 g of tyrosine given twice daily seemed to provide a "pick-up" for about 2 hours.

Similar benefits were seen with 2g of tyrosine daily in a double-blind, placebo-controlled trial of 21 military cadets exposed to physical and psychological stress.10

Depression

A pilot study that enrolled nine individuals is widely quoted as proving that tyrosine can help depression.8 However, this study was too small to provide reliable results. A subsequent double-blind placebo-controlled study of 65 people with depression failed to find any benefit.9

Safety Issues

Tyrosine seems to be generally safe, though at high dosages some people have reported nausea, diarrhea, vomiting, or nervousness. As with any other supplement taken in multigram doses, it is important to use a high-quality product; even a very small percentage of contaminant in the product might add up to a dangerous amount.

Maximum safe dosages for young children, women who are pregnant or nursing, or those with severe liver or kidney disease have not been established.

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