Evidence supporting the use of: L-tyrosine
For the body system: Thyroid Gland

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Synopsis

Source of validity: Scientific
Rating (out of 5): 2

L-tyrosine is an amino acid that plays a direct role in the synthesis of thyroid hormones. The thyroid gland produces two primary hormones, thyroxine (T4) and triiodothyronine (T3), both of which are synthesized from tyrosine and iodine. This biochemical relationship is well-established in physiology textbooks and scientific literature. In cases of severe dietary deficiency of tyrosine, thyroid hormone production could theoretically be impaired, as tyrosine is a structural precursor. However, tyrosine deficiency is rare in populations with adequate protein intake, and the vast majority of people synthesize enough tyrosine from phenylalanine or obtain sufficient amounts from dietary sources. Clinical studies specifically investigating L-tyrosine supplementation for thyroid support in healthy or hypothyroid individuals are limited. Most research has focused on populations with inherited metabolic disorders or under acute stress. There is no strong evidence that L-tyrosine supplementation improves thyroid function in people with normal diets or established hypothyroidism unrelated to protein malnutrition. Therefore, while the scientific basis for the role of tyrosine in thyroid hormone synthesis is clear, the evidence supporting supplemental L-tyrosine as a thyroid support intervention is weak, meriting a low evidence rating.

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