Optimizing Thyroid Hormone Conversion

This post is adapted from a chapter in my best-selling Essential Thyroid Cookbook. Enter your name and email to the left (scroll down a bit) for a sample cookbook.

[Minor updates: March 2, 2022 and November 9, 2022]

Often, when we think about optimizing thyroid function, we tend to focus on getting thyroid hormones balanced, whether that’s with thyroid hormone replacement or nutritional/lifestyle modifications (or both).

Go here for a functional thyroid panel, with reference ranges >

While optimizing thyroid hormones is a worthy effort, one missing piece of the conversation is often thyroid hormone conversion.

T4 is mostly inactive (“the lame duck”) and is the forerunner to T3, the predominant and more active hormone (“the big daddy”). If the body is to utilize thyroid hormones properly, the wheels that grease the T4 to T3 conversion need to be well oiled. 

Conversion can become compromised due to:

- Gut dysbiosis—an Elimination Provocation experiment will largely address this, although I highly suggest a fecal analysis (which we offer as part of our private coaching program) to determine if any gut infections are present

Mineral deficiencies, especially zinc, selenium, and iodine—my cookbook goes into detail about how these micronutrients benefit the thyroid (and immune system)

- Exposure to toxic halogens like fluoride, bromine, and chlorine

- Inadequate beneficial gut bacteria—a whopping 20 percent of T4/T3 conversion occurs in the presence of friendly gut bacteria (I highly recommend probiotic supplementation, with the consideration that for those with allergy/histamine/mast cell issues, you want to be careful and specific about your probiotic strains, as some are histamine inducers, especially Lactobacillus bulgaricis, Lactobacillus casei, Lactobacillus delbrueckii, and S. thermophilus. I can’t claim that this is an exhaustive list.)

- Impaired liver function—another whopping 20 percent of conversion takes place in the liver (A diet high in fiber, drinking warm lemon water (if tolerable—can incite a histamine response), and the herbs dandelion root and milk thistle can go a long way here.)

- The presence of yeast/candida

- Heavy metal exposure, especially mercury

- Radiation exposure

Estrogen dominance

- The use of birth control pills

Systemic inflammation

- Low tyrosine, often due to inadequate protein intake—my cookbook goes into detail about the importance of tyrosine

- Certain pharmaceuticals

- High cortisol/adrenal dysfunction/HPA (hypothalamic-pituitary-adrenal) axis dysfunction—go here for my Restore Your Adrenals guide

Imbalances in any of these areas could be why you’re not benefitting from your T4 medication. I hear it all the time…I’m on Synthroid, but I don’t feel any differently. Synthroid is just synthetic T4, which is what makes conversion especially important for people on T4 thyroid hormone replacement. (Synthroid is a brand name of Levothyroxine and other brand names include: Tirosint, Levoxyl, Unithroid, and Levo-T.)

Our bodies are meant to naturally convert T4 to T3, but many are compromised in making that conversion for the above reasons.

Addressing the considerations above is just “good medicine” anyway. All are a recipe for optimizing your health and living your best life. The added benefit is that you’ll get way more mileage from any efforts—pharmaceutical or nonpharmaceutical—in optimizing your thyroid health. 

If you’d like to talk through any of this, I invite you to schedule a Jumpstart session with me. Rest assured, it IS a coaching session and at the end of the conversation, I’ll share with you what it would look like to move forward with a private coaching program. 


When you mention radiation, I automatically think wifi, EMF, and computer screens. Are they a source of concern?

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