Phenylalanine and Tyrosine Dosing and Precautions

PhenylalaniNE

• A precursor for neurotransmitter biosynthesis
• One of 20 essential amino acids that the body cannot synthesize

L-phenylalanine is an essential amino acid (cannot be produced by the body) and thus must be obtained through the diet. Phenylalanine is used in different biochemical processes to produce neurotransmitters, dopamine, norepinephrine, and epinephrine. It is claimed but not proven that phenylalanine can promote sexual arousal, and there is evidence that phenylalanine can increase mental alertness (Grevet et al. 2002) and release hormones affecting appetite. D-phenylalanine has been shown to inhibit the metabolism of opiate-like substances called enkephalins in the brain. It is claimed that DL-phenylalanine is effective in the treatment of chronic pain (Walsh et al. 1986; Russell et al. 2000). There is some evidence that phenylalanine can help to overcome alcoholism and other drug addictions.

There have been reports that L-phenylalanine can promote high blood pressure in those predisposed to hypertension. Therefore, it is important to start off using moderate doses of phenylalanine, about 500 mg a day, and slowly work up to 1500 mg a day. Monitoring in the first few months on phenylalanine can detect blood pressure increases in the minority of people who will have this symptom. In fact, a Chinese study demonstrated the possible implication of phen-ylalanine in hypertension. The study looked at rat offspring whose parents and grandparents had essential hypertension (without known cause or preexisting renal disease) and stroke and compared them to those without a genetic predisposition to essential hypertension. By comparing the radioactive counts of phenylalanine and concentration in blood and tissue after administration of a phenylalanine substance, the researchers found that "A unique aberrant of metabolic kinetics of phenylalanine might be implicated in the inherited pathogenesis of essential hypertension and stroke . . . ." (Zhao et al. 2001).

Phenylalanine can promote the cell division of existing malignant melanoma cells. If you have melanoma, or any other form of cancer for that matter, avoid phenylalanine. According to a study in the Journal of Human Nutrition and Dietetics, three patients with metastatic melanoma and three with metastatic breast cancer took part in a study that involved a diet of phenylalanine and tyrosine administered at a very low dose (10 mg/kg/day for 1 month). The results were not good. Researchers reported that all the patients experienced anxiety and depression and other side effects. They also lost weight. The authors of this pilot study concluded: "Low phenylalanine and tyrosine diets do not appear to be a viable treatment option for patients with advanced cancer" (Harvie et al. 2002).

Persons who have PKU (phenylketonuria) cannot use phenylalanine. This includes those born with a genetic deficiency that prevents them from metabolizing phenylalanine (Walter et al. 2002).

TyrosiNE

• A precursor for biosynthesis of neurotransmitters
• A precursor for adrenaline and thyroid hormones
• Used to treat depression, anxiety, and allergies
• Combined with tryptophan to treat drug abuse
• Suppresses appetite
• Tyrosine deficiency will result in depression and mood disorders
• As a dietary precursor, one of the major nutritional ingredients that affects neurotransmitter synthesis and brain functions

Tyrosine is a nonessential amino acid synthesized in the body from phenylalanine. It is an important nutritional ingredient and factor for biosynthesis of the brain neurotransmitters epinephrine, norepinephrine, and dopamine. Tyrosine is also used to produce one of the major hormones, thyroxin, which plays an important role in controlling metabolic rate, skin health, mental health, and growth rate.

Tyrosine is specifically used to treat depression because it is a precursor for those neurotransmitters that are responsible for transmitting nerve impulses and essential for preventing depression. In fact, in a study of healthy women who underwent phenylalanine/tyrosine depletion, the results showed a lowering of mood (Leyton et al. 1999). Another study, this time with healthy male volunteers in a randomized, double blind study, reinforced the earlier research (Grevet et al. 2002). Results were similar in that the men, after being fed deficient phenylalanine/tyrosine mixtures, experienced depressed mood and alertness.

Tyrosine has been tested on humans for increasing their endurance to anxiety and stress under fatigue. It was proven in research studies that tyrosine supplementation results in increased performance over a control group (Avraham et al. 2001). Tyrosine was also used with the amino acid tryptophan for treatment of cocaine abuse (Tutton et al. 1993).

Tyrosine is a mild antioxidant, reacting with free radicals that can cause damage to cells. It is also thought that tyrosine promotes sexual drive. Tyrosine may also be used as a mild appetite suppressant.

SUMMARY

1. Phenylalanine may be effective in alleviating chronic pain, hunger, and depressed feelings.
2. L-tyrosine shares some of the characteristics of phenyalanine and may be effective in ameliorating Parkinson's disease and certain thyroid disorders.
3. The family of neurotrophin proteins, including nerve growth factor (NGF), brain-derived nerve factor (BDNF), and neurotrophins (NT-3, NT-4/5, and 6), require tyrosine and tryptophan as precursors to synthesis.
4. Dietary precursors such as phenylalanine, tyrosine, tryptophan, and choline, especially in purified form, have been shown to promote the formation of neurotransmitters in the brain. When taken orally or parenterally, they induce an increase of transmitter formation, further influencing a variety of brain functions.
5. Plasma levels of tyrosine can be elevated incrementally depending on dose.

• Suggested dosage: Start off early in the day with 500 mg of phenylalanine or tyrosine and gradually increase to 1500 mg a day.

Tyrosine or phenylalanine may promote cancer cell division, especially malignant melanoma. Have your blood pressure checked, especially during the first 3 months of dosing, to make sure phenylalanine or tyrosine is not inducing hypertension. Persons with PKU (phenylketonuria) cannot use phenylalanine. This includes those born with a genetic deficiency that prevents them from metabolizing phenylalanine.

Product availabiliTY

L-phenylalanine, tyrosine, lecithin, and choline can be ordered by calling (800) 544-4440 or by ordering online.