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L Phenylalanine
Overview

Phenylalanine is an essential amino acid (a building block for proteins in the body), meaning the body needs it for health but cannot make it. You have to get it from food. Phenylalanine is found in three forms: L-phenylalanine, the natural form found in proteins; D-phenylalanine (a mirror image of L-phenylalanine that is made in a laboratory), and DL-phenylalanine, a combination of the two forms.
The body changes phenylalanine into tyrosine, another amino acid that's needed to make proteins, brain chemicals including L-dopa, epinephrine, and norepinephrine, and thyroid hormones. Because norepinephrine affects mood, different forms of phenylalanine have been proposed to treat depression. Symptoms of phenylalanine deficiency include confusion, lack of energy, depression, decreased alertness, memory problems, and lack of appetite.
On the other hand, a rare metabolic disorder called phenylketonuria (PKU) occurs in people who are missing an enzyme that the body needs to use phenylalanine. This causes high levels of phenylalanine to build up. If it is not treated before 3 weeks of age, PKU can cause severe, irreversible mental retardation. In the United States, newborns are tested for PKU during the first 48 - 72 hours of life. People with PKU must eat a diet that avoids phenylalanine and take tyrosine supplements to have optimum brain development and growth.

What is Phenylalanine?

L_Phenylalanine
2-Amino-3-phenylpropanoic acid
 

Phenylalanine is an amino acid, a “building block” of protein. There are three forms of phenylalanine: D-phenylalanine, L-phenylalanine, and the mix made in the laboratory called DL-phenylalanine. D-phenylalanine is not an essential amino acid, and its role in people is not currently understood. L-phenylalanine is an essential amino acid and is the only form of phenylalanine found in proteins. The body uses phenylalanine to make chemical messengers, but it is not clear how phenylalanine might work.

How is it Made?
Phenylalanine is found naturally in the breast milk of mammals. It is used in the manufacture of food and drink products and sold as a nutritional supplement for its reputed analgesic and antidepressant effects. It is a direct precursor to the neuromodulator phenylethylamine, a commonly used dietary supplement.

Where is it Found?
L-phenylalanine is found in most foods that contain protein such as beef, poultry, pork, fish, milk, yogurt, eggs, cheese, soy products (including soy protein isolate, soybean flour, and tofu), and certain nuts and seeds. The artificial sweetener aspartame is also high in phenylalanine. D-phenylalanine is made in the laboratory but is not found in food.

Product related PDF file
Behavioral Effects of Phenylalanine
Dietary Phenylalanine And Brain Function
D-Phenylalanine for Pain Endurance
 

Benefits / Uses
Chronic pain
D-phenylalanine (but not L-phenylalanine) has been proposed to treat chronic pain, but so far the studies have not shown good evidence that it works. Two studies that appeared to show positive results had flaws that made the findings unreliable. Other clinical studies have found D-phenylalanine to be no more effective than placebo in reducing pain.
Parkinson's disease
One animal study suggests that D-phenylalanine may improve rigidity, walking disabilities, speech difficulties, and depression associated with Parkinson's disease.


Vitiligo
A skin condition called vitiligo. Taking L-phenylalanine by mouth in combination with UVA exposure or applying L-phenylalanine to the skin in combination with UVA exposure seems to be effective for treating vitiligo in adults and in children.
Depression
Some clinical studies suggests that phenylalanine may be helpful as part of a comprehensive therapy for depression. However, most of the studies were done in the 1970s and 1980s and were not rigorously tested. People have reported that their mood improved when they took phenylalanine. Researchers think this is because phenylalanine increases production of brain chemicals, such as dopamine and norepinephrine.

Dosage
Recommended dosages of phenylalanine vary depending on the health condition being treated. Take supplements 15 - 30 minutes before meals. The daily recommended dietary allowances (RDAs) for L-phenylalanine are as follows. Note this is for getting phenylalanine from food, not supplements.

Pediatric
Infants 0 - 4 months: 125 mg per kilogram of body weight
Children 5 months - 2 years: 69 mg per kilogram of body weight
Children 3 - 12 years: 22 mg per kilogram of body weight
The combination of oral and topical phenylalanine (together with ultraviolet light) is used to treat children with vitiligo. The dose is determined by a doctor.


Adults
Teenagers and adults: 14 mg per kilogram of body weight.
Some experts suggest that adults may need as much as 39 mg per kilogram of body weight per day for general health. Doses as high as 50 - 100 mg per kilogram have been used in studies of those with vitiligo. The most common amounts used range from 750 - 3,000 mg per day for adults.

Possible Side-Effects / Precautions / Possible Interactions
L-phenylalanine is possibly safe for most people, even in amounts needed as medicine.

Special Precautions & Warnings:
Pregnancy and breast-feeding: Having too much phenylalanine in the mother’s system during pregnancy can increase the chances of birth defects. The risk for facial defects is highest at weeks 10-14, nervous system and growth defects between 3-16 weeks, and heart defects at 3-8 weeks. For women who process phenylalanine normally and have normal levels, it’s probably fine to get the amount of phenylalanine found in food, but not in higher doses. Don’t take supplements. For women who have high levels of phenylalanine, even normal food amounts are unsafe. Additionally, experts recommend a low phenylalanine diet for at least 20 weeks before getting pregnant. This should reduce the risk of birth defects.
It is likely safe for breast-feeding mothers whose bodies process phenylalanine normally to consume the amount of phenylalanine found in food. But don’t take more. Not enough is known about the safety of taking phenylalanine in medicinal amounts during breast-feeding.
Phenylketonuria (PKU) and other conditions that cause high levels of phenylalanine: Phenylalanine should be avoided in people with certain inherited disorders that cause their bodies to build up too much phenylalanine. Phenylketonuria (PKU) is one of these diseases. People with this disorder can develop mental retardation, high blood pressure, stroke, and many other serious health issues if they consume phenylalanine. PKU is so serious that babies are screened at birth to determine whether they have the disorder and will need a special diet to avoid these problems.
Schizophrenia: Use with caution. Phenylalanine can make a movement disorder (tardive dyskinesia) in people with schizophrenia worse.

Possible Interactions
Monoamine Oxidase Inhibitors - Monoamine oxidase inhibitors (MAOIs) are an older class of antidepressants drugs that are rarely used now. They include phenelzine (Nardil), isocarboxazid (Marplan), and tranylcypromine sulfate (Parnate). Taking phenylalanine while taking MAOIs may cause a severe increase in blood pressure (hypertensive crisis). This severe increase in blood pressure can lead to a heart attack or stroke. People taking MAOIs should avoid foods and supplements containing phenylalanine.

Baclofen - Phenylalanine may reduce absorption of baclofen (Lioresal), a medication used to relieve muscle spasms. Avoid taking Baclofen with a meal, especially one that is high in protein, or with phenylalanine supplements.
Levodopa - A few case reports suggest that phenylalanine may reduce the effectiveness of levodopa (Sinemet), a medication used to treat Parkinson's disease. Some researchers think phenylalanine may interfere with the absorption of levodopa.
Selegiline - L-phenylalanine and the selective MAO inhibitor selegiline (Eldepryl, Deprenyl) may strengthen the antidepressant effects of phenylalanine. They should not be taken together.

Antipsychotic or neuroleptic drugs - L-phenylalanine may worsen tardive dyskinesia, a side effect of these neuroleptic drugs. These drugs include phenytoin (Dilantin), valproic acid (Depakene, Depakote), and carbamazepine (Tegretol), among others.
Reviewed last on: 6/8/2009
Steven D. Ehrlich, NMD, Solutions Acupuncture, a private practice specializing in complementary and alternative medicine, Phoenix, AZ. Review provided by VeriMed Healthcare Network.

Research Studies / References
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Borison RL, Maple PJ, Havdala HS, Diamond BI. Metabolism of an amino acid with antidepressant properties. Res Commun Chem Pathol Pharmacol. 1978;21(2):363-6.
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