Total T4

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What is Total T4?

T4, or thyroxine, is the main thyroid hormone produced by the thyroid gland. Once released into the bloodstream, TSH (thyroid-stimulating hormone) stimulates the thyroid gland to produce T4 and T3 (triiodothyronine). T4 exists in two forms: bound T4 (attached to proteins) and free T4 (unbound and able to enter tissues). A Total T4 test measures both bound and free T4 together. About 90% of thyroid hormone circulating in the blood is T4, and most of it is converted to the active T3 form in the liver and other tissues. While bound T4 remains in the bloodstream as a reserve supply, only free T4 can enter cells and exert its metabolic effects.

Why is Total T4 important?

Tracking your Total T4 levels helps assess the health of your thyroid gland, which is critical to your endocrine system. Thyroid hormones regulate metabolism, heart function, digestive processes, muscle control, brain development, and bone maintenance. Because of its significance, Total T4 is included in SiPhox Health‘s Thyroid+ panel.
High Total T4 may indicate hyperthyroidism (overactive thyroid gland), which can be caused by Graves disease, thyroiditis, or toxic thyroid nodules. Low Total T4 may point to hypothyroidism (underactive thyroid gland). Symptoms of hyperthyroidism include weight loss, rapid or irregular heartbeat, increased hunger, and anxiousness among other issues. Symptoms of hypothyroidism include fatigue, weight gain, cold sensitivity, thinning hair, constipation, and other physical and mental issues. If you are concerned with your levels, it is important to consult with your physician.

How can I better understand my Total T4 levels?

Total T4 test results are analyzed in conjunction with other thyroid tests such as TSH and free T4 to determine whether the thyroid gland is functioning properly. It is important to note that Total T4 levels can be affected by medications and conditions that change thyroid hormone binding proteins. Pregnancy, birth control pills, and estrogen can increase Total T4, while testosterone and certain other medications can decrease it. In these cases, free T4 testing may be more accurate.

How can I maintain optimal Total T4 levels?

If you need to maintain or adjust your Total T4 levels, consider the following strategies:
Dietary Changes: Ensure adequate iodine intake from sources like seafood, eggs, dairy products, and iodized salt, as iodine is essential for thyroid hormone production. Include foods rich in selenium (Brazil nuts, fish, mushrooms) and zinc (meat, seafood, nuts) which support thyroid function and T4 to T3 conversion. If taking thyroid medication, avoid consuming large amounts of soy products around the time of medication as it may interfere with absorption.
Lifestyle Changes: Manage stress through techniques like yoga or meditation, as chronic stress can disrupt thyroid function. Engage in regular physical activity including cardiovascular exercise and strength training to support metabolic health. Prioritize quality sleep and maintain a balanced diet rich in fruits, vegetables, lean proteins, and whole grains to support overall thyroid health.

Where can I learn more?

• MedlinePlus – Thyroxine (T4) Test
• American Thyroid Association – Thyroid Function Tests
• Cleveland Clinic – T4 (Thyroxine) Test
• PMC – The Role of Nutrition on Thyroid Function
• Cleveland Clinic – Diet for Hypothyroidism

DISCLAIMER: This information is for educational purposes only and is not a substitute for professional medical advice. Always consult your healthcare provider for interpretation of your results and for personalized health recommendations.