Tyrosine is a non-essential amino acid obtainable either through diet or body synthesis and used in many bodily processes. Tyrosine is synthesized from another amino acid, phenylalanine, found in many high-protein foods such as meats, fish, nuts and dairy products. Tyrosine plays an important role in the production of brain chemicals and hormones, specifically dopamine and serotonin, powerful neurotransmitters, and melanin, an important pigment-producing hormone. The recommended daily allowance of tyrosine is about 1 to 3 g. Overdosing with tyrosine is exceptionally rare; however, excess amounts of tyrosine may have adverse effects on conditions like hyperthyroidism, Graves' disease and some mental conditions.
Hyperthyroidism
Hyperthyroidism is a condition in which your thyroid glands produce excess thyroxine, a thyroid hormone that helps control metabolism. Individuals with hyperthyroidism may experience fatigue, excessive sweating, an enlarged thyroid, unexplained weight loss, high blood pressure and heart palpitations. Your body uses tyrosine to make thyroxine, which may make the symptoms of hyperthyroidism worse. If you suffer from hyperthyroidism, it is not recommended to ingest large amounts of tyrosine.
Graves' Disease
Graves' disease is a form of hyperthyroidism that involves an autoimmune response to the overproduction of thyroxine. In Graves' disease, your immune system will begin attacking your thyroid gland, causing thyroid hormone production to increase drastically. Consuming large amounts of tyrosine will increase the production of thyroxine, increasing the severity of the symptoms associated with general hyperthyroidism but may also lead to a condition known as Graves' ophthalmopathy. This condition causes your eyeballs to bulge out past their sockets due to a swelling of the tissues behind them.
Mental Conditions
While normal levels of tyrosine promote the production of neurotransmitters in your brain, high levels of tyrosine may actually inhibit neurotransmitter production. High plasma concentrations of tyrosine in your brain may reduce dopamine production, an important neurotransmitter that plays a role in your mood. Low dopamine levels may lead to fatigue and depression and can worsen the symptoms of Parkinson's disease. High amounts of tyrosine decrease the absorption of some of the amino acids responsible for L-dopa production, a precursor to dopamine.
Lethal Levels of Tyrosine
The lethal toxicity of tyrosine is exceptionally high, making fatal doses of tyrosine very rare. Current research on rates suggests that a lethal dose of tyrosine involves consuming about 5,000 mg per kg of body weight. This means a lethal dose for an adult 165 lb. or 75 kg is 375 g or 375,000 mg of tyrosine. Therefore, the risk of death due to the toxicity of tyrosine appears to be extremely low.
References
- "Human Anatomy and Physiology"; Elain N. Marieb; 2004
- "Encyclopedia of Nutritional Supplements"; Michael T. Murray; 1996
- PubMed Health; Hyperthyroidism; April 2010
- MayoClinic: Graves' Disease
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