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Thyroid disorders are the most commonly diagnosed hormone imbalance. Many people take thyroid supplements. But, what most people don’t know is how their other hormones can affect their thyroid levels.

Let’s cover some important background information on thyroid hormones to help us understand.

Levothyroxine (T4) and Liothyronine (T3) are two thyronines (thyroid hormones) which help control the bodies metabolism, regulate protein, and assist with bone growth. T4 has 4 iodine molecules, and that is why it is called T4. It has a long half-life, and acts as a reservoir, or storage depot, for T3, the active thyroid hormone. T3 has 3 iodine molecules. T4 is converted to T3 in the body by Iodothyronine Deiodinase, an enzyme which breaks off one of the four Iodine molecules.

The action of Iodothyronine Deiodinase requires adequate protein, selenium, zinc, and iodine. If you are low in any one of these, T4 will not convert to T3 and you will have symptoms of low thyroid even though your lab tests (TSH and T4) will indicate that you are fine. This is called functional hypothyroidism. High cortisol (stress hormone) can also block the conversion of T4 to T3. For this reason, I do recommend a Free T3 test when doing labs.

Thyroid T4 To T3

Thyroid T4 To T3

How do other hormones interfere with thyroid function?

If your estrogen is high, or you do not have adequate progesterone, it can block the action of T3, causing a functional hypothyroid state. High cortisol (the stress hormone) can oppose the action of T3. Because cortisol is required for the action of T3 in the cell, not having enough cortisol can also cause a functional hypothyroidism.

T3 Binding At Cell

T3 Binding At Cell


What are the symptoms of hypothyroidism (Low thyroid function)?

  • Brittle hair and nails. Nails typically have vertical ridges. Hair falls out.
  • Cold hands, feet, or nose
  • Tired and fatigued. Decreased stamina and foggy thinking.
  • Thin skin
  • Puffy eyes
  • High triglycerides and cholesterol
  • Decreased sweating
  • Hoarseness
  • Fibromyalgia and Uterine Fibroids
  • Constipation

If you believe you are experiencing functional hypothyroidism, please allow me to help you. I will work with you and your practitioner to optimize your diet and thyroid supplements to alleviate symptoms. Contact me and allow me to help you heal.