Tyrosine is an amino acid that is necessary for your body to make various proteins such as neurotransmitters, chemicals that your nerve cells use to transmit messages. Your body uses another amino acid called L-phenylalanine from food to make tyrosine, which does not occur naturally in food. L-phenylalanine is found in protein-containing foods.
Sources
L-phenylalanine is an essential amino acid found in foods such as meat, poultry, eggs, fish, soy products, beans, some nuts, seeds and dairy foods, according to the University of Maryland Medical Center. Since L-phenylalanine is widely available in foods, deficiencies in Americans are not common. Because phenylalanine is required for proper brain function, low levels can lead to symptoms such as loss of appetite, fatigue, depression, memory problems and confusion.
Deficiency
The RDA or recommended dietary allowance of L-phenylalanine is 14 milligrams per kilogram or 2.2 pounds of body weight, although some experts believe it should be as much as 39 milligrams per kilogram. Children, since they are actively growing, require higher amounts than adults, the younger they are. Infants may need up to 125 milligrams per kilogram. If born in the United States, they are routinely tested for phenylketonuria or the inability to use phenylalanine, which can result in mental retardation.
Supplementation
D-phenylalanine is a synthetic form available in supplements, but not in food. DL-phenylalanine is a mixture of the natural and synthetic forms, also available in supplement form, according to the Langone Medical Center. You can buy both as a tablet, capsule or powder. The RDA for phenylalanine refers to what you get in food. RDAs have not been set for supplements, although typical dosages range for adults are between 750 and 3,000 milligrams a day.
Additional Information
Consult with your doctor about using supplements, as interactions with drugs like antipsychotics can occur. Higher doses of supplements may be prescribed to treat conditions like depression, pain and vitiligo, a skin condition. Whether the long-term use of supplements is safe is not known. In addition, maximum safe limits for supplementation have not been established for children, pregnant or lactating women, or those who have serious liver or kidney conditions.
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