L-Tyrosine is the left-handed isomer of the aromatic amino acid tyrosine. It is a naturally occurring tyrosine that is synthesised in the body from L-phenylalanine. It is considered a non-essential amino acid. However, it is considered an essential nutrient for people with phenylketonuria who lack the enzyme phenylalanine hydroxylase and are unable to convert phenylalanine into tyrosine. In the body, tyrosine plays a role in protein synthesis and is a precursor for the synthesis of catecholamines, thyroxine and melanin.

Food Sources

L-Tyrosine can be obtained through the daily diet and is commonly found in the following foods:

• Soy products (soybeans, lima beans)

• Meat (chicken, turkey, fish)

• Fruits (avocados, bananas)

• Dairy products (milk, cheese, yogurt, cottage cheese)

• Nuts (peanuts, almonds)

• Other (pumpkin seeds, sesame seeds)

Actions and Effects

L-Tyrosine has a wide range of uses in the pharmaceutical, cosmetic, and food industries due to its ability to improve memory, antidepressant, sleep aid, and inhibit melanin production. It is used as a precursor for the synthesis of the catecholamines dopamine (DA) and norepinephrine (NE). DA and NE are depleted under stressful conditions, which can impair cognitive function. Supplementation with L-Tyrosine may be helpful in helping to alleviate acute stress-induced cognitive decline by restoring catecholamine levels in the brain.

Dosage and Side Effects

The dosage of L-Tyrosine when used as a supplement varies and needs to be taken under the advice of a doctor or dietitian. The recommended oral dosage for healthy adults is 100-300 mg/kg per day. It is generally well tolerated with no serious adverse effects, although some patients may experience side effects such as nausea, headache, fatigue, and heartburn.