The body uses phenylalanine to manufacture tyrosine — both of which are amino acids, or the building blocks of protein. According to experts, tyrosine and the thyroid are closely connected. Tyrosine assists thyroid hormone regulation as well as the function of the adrenal and pituitary glands. Along with iodine, the body uses tyrosine to produce thyroid hormones that keep the body’s metabolism running in tip-top shape. Low levels of tyrosine have been associated with hypothyroidism, the clinical term for an underactive thyroid.
Some experts say that a deficiency of tyrosine can increase the chances of hypothyroidism; however, deficiencies of tyrosine are rare. Hypothyroidism is a condition in which a lack of thyroid hormones causes the body to slow down. Symptoms of this condition include weight gain, depression, constipation and cold intolerance as well as dry hair and skin. Severe hypothyroidism may also lead to anemia, mental confusion and a serious, life-threatening condition known as myxedema, which can result in a coma. Untreated hypothyroidism in infants can even cause developmental retardation.
Deficiencies of tyrosine are apparently rare, since this amino acid is present in a variety of foods. While there is a link between low levels of tyrosine and the thyroid, this amino acid is readily available in the average diet. Dietary sources of tyrosine include milk, cheese, yogurt, eggs, chicken and turkey as well as some legumes and seeds, like lima beans, pumpkin and sesame seeds. This amino acid can also be found in soy products, wheat and oats.
Those who suspect a link between low levels of tyrosine and the thyroid should first consult a physician for a blood test to confirm underactive thyroid function. This is especially important since the efficacy of over-the-counter tyrosine has not been conclusively proven as of 2011. There is a negative connection between tyrosine and the thyroid in people with hyperthyroidism or Graves disease — a condition in which the thyroid produces too much thyroid hormone. For these people, tyrosine can increase thyroid function and worsen their disease.
Tyrosine is often recommended for people with a serious condition called Phenylketonuria (PKU). Persons with this condition must avoid ingesting phenylalanine, the amino acid that produces tyrosine. The consumption of phenylalanine can cause brain damage in those suffering from PKU, so a specially formulated combination of proteins and tyrosine is prescribed for these patients.
The supervision of a doctor is always recommended when taking tyrosine supplements. Drug interactions can occur, as tyrosine has been known to interfere with certain anti-depressants. According to some sources, this medication has also has been associated with migraine headaches.