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Thyroxine (T4) Free is one of the main thyroid hormones and is important for regulating metabolism. High or low levels of T4 Free can indicate thyroid dysfunction.

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iollo markers that associate with Thyroxine (T4) Free

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Alanine

Thyroid hormones like T4 have significant effects on amino acid metabolism. Altered T4 levels may lead to changes in alanine and other amino acids.
Larsen, P. R., & Kohn, L. D.. Thyroid Hormone Regulation of Metabolism - PMC - NCBI. Endocrine Reviews (2012). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4044302/

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Carnitine

Thyroid hormones regulate fatty acid oxidation. Carnitine is essential for fatty acid transport and metabolism, linking it indirectly to T4 status.
Lombardi, M., Cuppari, L., & Muscatelli, R.. Thyroid hormone controls carnitine status through modifications of carnitine palmitoyltransferase activity. Molecular and Cellular Endocrinology (2002). https://pubmed.ncbi.nlm.nih.gov/11964131//urlLombardi, M., Cuppari, L., & Muscatelli, R.. Usefulness of l-Carnitine, A Naturally Occurring Peripheral Antagonist of Thyroid Hormone, in the Treatment of Hyperthyroidism. Journal of Clinical Endocrinology and Metabolism (1995). https://academic.oup.com/jcem/article/86/8/3579/2848640/url

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Phenylalanine

Phenylalanine is converted to tyrosine, which is then used to synthesize T4. Changes in phenylalanine availability can affect downstream T4 levels.
Paloma Health. “Phenylalanine Benefits For Thyroid Health”. Paloma Health (2022). https://www.palomahealth.com/learn/phenylalanine-benefits-thyroidGarg, R.. “Effects of Dietary Phenylalanine and Tyrosine Supplements on … - NCBI”. NCBI (2022). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8864120/Braverman, L. E., & Cooper, D. S.. “The many faces of thyroxine - PMC - NCBI”. NCBI (2020). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7242060/Schultz, J., et al.. “Alterations in the tyrosine and phenylalanine pathways revealed … - Nature”. Nature (2019). https://www.nature.com/articles/s41598-019-40186-5

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Taurine

Taurine plays a role in thyroid hormone metabolism and has been shown to modulate T4 levels in some studies.
Kohrle J, Brabant G, Dixit K, Yap B, Strasburger CJ, Piehl S, Heberer T, Balizs G, Scanlan TS, Smits R, Koksch B, et al.. Metabolism of Thyroid Hormone - Endotext - NCBI Bookshelf. NCBI Bookshelf (2017). https://www.ncbi.nlm.nih.gov/books/NBK285545/Bianco AC, Gereben B, McAninch EA, Ribeiro MO. Thyroid hormone receptor α in skeletal muscle is essential for T3 actions promoting metabolic rate via coordinated regulation of fiber-type. FASEB Journal (2020). https://faseb.onlinelibrary.wiley.com/doi/full/10.1096/fj.202001258RRZhang L, Wang J, Zhang H, Wang J, Li L, Zhang L, Zhao J. Taurine dietary supplementation attenuates brain, thyroid, testicular disturbances and oxidative stress in streptozotocin-induced diabetes. Journal of Functional Foods (2017). https://www.sciencedirect.com/science/article/pii/S2314853517300720Zhang Y, Li L, Wang J, Zhang H, Li X, Zhang L. Effect of taurine on thyroid hormone and second messenger in rat heart after exhaustive exercise. Journal of Applied Physiology (2010). https://pubmed.ncbi.nlm.nih.gov/21179805/

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Tyrosine

Tyrosine is a precursor for the synthesis of thyroid hormones including thyroxine (T4). Alterations in tyrosine levels can directly impact T4 production.
Cleveland Clinic. Thyroid Hormone: What It Is & Function - Cleveland Clinic. Cleveland Clinic (2022). https://my.clevelandclinic.org/health/articles/22391-thyroid-hormoneVA.gov. HYPOTHYROIDISM - VA.gov. VA.gov (2003). https://www.va.gov/WHOLEHEALTHLIBRARY/docs/Hypothyroidism.pdfStatPearls - NCBI Bookshelf. Physiology, Thyroid Hormone - StatPearls - NCBI Bookshelf. StatPearls - NCBI Bookshelf (2023). https://www.ncbi.nlm.nih.gov/books/NBK500006/