Ah Thyroid conversion! The elephant in the room. While many focus on pathology results, medication and supplements, what if there is a secret cellular block sabotaging your best efforts?

While our thyroid produces mostly T4 hormones they are largely inactive and of little use to the body. First, T4 needs to be converted into T3 so that it can actually fill receptors sites in our cells to do their job to help us feel less zombified and more like ourselves. Receptor sites are found in every cell in our body and they are distinctly T3 shaped, not T4. 

Who among us is old enough to remember cheques? T4 is like the $20 cheque you got in your birthday card. You can’t spend it and it’s pretty useless until it has been deposited into your bank account. Once it is in your bank account you can then withdraw it as cash, kind of like thyroid hormone conversion. Cash has value and can be spent, like T3. Until and IF the conversion process has occurred, your thyroid hormones are not able to properly do their thang in your brain, reproductive, gut, liver, cardiovascular and muscular cells so you could still be symptomatic.

Cellular Hypothyroidism

Cellular hypothyroidism is when you have adequate thyroid hormones but conversion is poor or something is blocking the active T3 thyroid hormones from entering the cells (more about that below).

The interesting and infuriating thing about poor thyroid hormone conversion is that you can’t always tell on paper. Your TSH and T4  levels can look ok in pathology results but behind the scenes you can be in a state of what we call cellular hypothyroidism where the cells themselves aren’t getting the T3 goods. So, are there people out there struggling with hypothyroid symptoms that can’t get answers or a diagnosis because their pathology isn’t telling the whole story? I certainly believe so and suspect worsening thyroid conversion to be one of the big drivers in the obesity epidemic we’ve been seeing in the past few decades.

How Thyroid Hormone Conversion Works

Conversion occurs via deiodinasation of T4 (named for its 4 iodine molecules) which removes one iodine molecule from T3 (named for its three iodine molecules). Deiodinase enzymes are mostly active in the gut & liver with a smaller percentage occurring in other tissues like the kidneys and the thyroid itself. If this process is impaired, you might still experience hypothyroid symptoms even if your blood tests show adequate T4 levels.

Factors Affecting Thyroid Hormone Conversion

1. Gut Health

Your gut plays a critical role in converting T4 to T3, with around 20% of this conversion happening in your intestinal tract. A healthy gut microbiome—the community of bacteria living in your digestive system—is essential for this process.

What impacts gut health?

• Gut dysbiosis: An imbalance in gut bacteria allowing some species to overgrow and dominate the beneficial bacteria, leading to a reduction in bacterial variety. One thing we know for sure is that you want a lot of variety in the bacterial species that reside in your gut.
• Intestinal permeability (AKA ‘leaky gut’): A damaged gut lining allows harmful substances into your bloodstream, triggering inflammation.
• Diet and stress: Processed foods, additives, poor blood sugar control and chronic stress will worsen gut health.

How to support your gut:

• Eat prebiotic foods (asparagus, onions, garlic) and probiotic-rich options (sauerkraut, kimchi, yogurt).
• Reduce/remove inflammatory foods for those with Hashimoto’s; gluten, processed foods, high sugar foods and often soy and dairy.
• Heal your gut lining with blood sugar control and microbiome restoration. Check out my Food Freedom for Hashimoto’s meal plan if you need guidance on how to do this, it’s not as difficult, expensive or unpalatable as you might think.
• Address underlying issues like infections (e.g., H. pylori or SIBO) if you have chronic IBS-like symptoms; bloating, excessive gas, reflux, disordered bowel motions, abdominal pain etc.

2. Liver Function

Your liver is responsible for converting about 60% of T4 into T3. A sluggish liver can impair this process, leaving you with less active thyroid hormone. The kicker? Your liver needs adequate T3 to function optimally! Vicious cycle…loading.

What impacts liver function?

• Poor diet and obesity, particularly high sugar and refined carbohydrate intake.
• Excessive intake/exposure to alcohol, some medications, smoking, pesticides, plastics, heavy metals and some conditions such as Gilbert’s syndrome, hepatitis, high viral load etc.

How to support your liver:

• Limit alcohol and environmental toxin exposure. 
• Stay hydrated to support detoxification pathways.
• Dandelion root & leaves, turmeric, ginger, garlic, leafy greens, green tea, cruciferous vegetables, citrus fruit, fatty fish, extra virgin olive and adequate protein all support both phase 1 and phase 2 detoxification pathways.

3. Nutrient Deficiencies

Your body needs certain nutrients for effective thyroid hormone conversion and unfortunately these are commonly low in Hashimoto’s and Hypothyroidism:

• Selenium: Crucial for converting T4 into T3 and reducing thyroid inflammation. Brazil nuts, eggs, and seafood are great sources. 
• Iron: Iron is essential for enzyme function in the conversion process. Red meat, particularly kangaroo, venison and shellfish are the most bioavailable sources of heme iron.
• Zinc: Another crucial nutrient for thyroid hormone conversion. Oysters, meat, poultry, fish, eggs, nuts and seeds will provide you with zinc.
• Vitamin D: Plays a supportive role in thyroid health and immune regulation. Don’t neglect some sunshine over summer to get your levels nice and high for winter. 

A note on supplements

While I do recommend a food first approach when it comes to a few nutrients such as iodine, selenium and iron I find that it is difficult or risky to use foods alone to correct nutrient deficiencies. Iron almost always needs a helping hand, especially if you are still menstruating or severely deficient which many Hashimoto’s sufferers are. Even with supplementation iron status can take 6-12 months to reach optimal levels. Iodine and selenium need to be monitored closely as they are two of the easiest nutrients to have too much of. Therefore eating large amounts from food sources may put you at risk of toxicity or may simply be more difficult to quantify, making treating deficiency that way difficult. Professional assessment of your pathology and specific dosing and reviews are necessary before you can maintain levels with diet alone. 

4. Hormonal Imbalances

High estrogen levels can block the conversion of T4 to T3. This is especially common during perimenopause, menopause, or in women with estrogen dominance due to environmental toxins or hormonal birth control.

Oestrogren lowering strategies:

• Detoxify excess estrogen by eating fiber-rich foods and cruciferous vegetables.
• Look to microbiome restoration to regulate high oestrogen levels as a dysbiotic gut will impact your oestrogen levels. 
• Look after your liver that works in concert with your gut to detoxify oestrogen and prevent build up, by eating cruciferous vegetables and following the liver loving advice above.
• Avoid endocrine-disrupting chemicals found in plastics, perfumes, cooking and food storage, cosmetics and personal care products. 

5. Genetics and Age

Some people have genetic variations (like DIO2 polymorphisms) that impair their ability to convert T4 to T3. Additionally, conversion tends to become less efficient with age.

What can you do?

• Speak to your healthcare provider about testing for genetic factors or trying T3 medication (liothyronine) or combination therapies like NDT (natural desiccated thyroid).
• If in doubt check your reverse T3 levels. 

6. High Cortisol

Yes, high cortisol directly blocks thyroid hormone conversion and can also impact thyroid hormone production too. Chronic (long term) stress increases TSH by signalling that less thyroid hormones are required, leading to hypothyroidism. This is why it’s really common to see periods of stress often due to divorce, death of a loved one or other trauma precede a change in thyroid function.

I feel like every blog I write ends like this so sorry if I sound like a broken record but basically, learn how to balance your blood sugar, address nutrient deficiencies, take loving tender care of your liver, make sure your gut health is super schmick and do whatever it takes to ensure you are only using fight or flight when you need it in the short term – like when you hear your car door opening in the middle of the night – which happened to me this week, now that was stressful!

Nailing these strategies will go such a long way to helping you feel amazing once again.

Pathology clues

You can’t always tell if conversion is poor in a regular thyroid panel but you can assess with:

• Elevated reverse T3 (blood test) can indicate your T3 is being shunted into reverse T3, rendering it inert again. It is not covered by medicare, not routinely ordered and is expensive.
• Basal temperature tracking.
• A thorough assessment of symptoms and health history with a patient forward approach.
• High T4 and low T3 can indicate that T4 is backing up due to poor conversion but this picture doesn’t always occur alongside high reverse T3, another crucial reason however, to always insist on testing both T4 and T3. 

Honestly though, before jumping to expensive tests start by supporting your gut, liver, hormones and wellbeing as you’ll give your body the best chance to convert thyroid hormones effectively and you might do your thyroid and immune system some good in the meantime. Basal temperature tracking is another free, non-invasive way you can track how well your metabolism and therefore your thyroid function is tracking.

So is your T4 medication actually being converted into T3 to tackle your hypothyroid symptoms? If you’re still exhausted, cold and gaining weight with low moods, hair loss or any number of hypothyroid symptoms, then it’s likely your conversion is not adequate. You might also want to talk to your prescribing doctor about T3 or a T4/T3 mixed medication. It comes pre-converted for your cellular convenience maam! It’s definitely not a silver bullet and doesn’t work for everyone but it’s worth exploring if what you’re currently doing isn’t helping with symptoms. 

THE best place to start with improving thyroid conversion is still to look to your gut, liver, stress, nutrient status & oestrogen levels and so much of that comes down to what we choose to consume. If you’re feeling a bit overwhelmed about the what, how & when of food I am currently working on my Food Freedom, Hashimoto’s Edition. I have created 45 breakfast, lunch & dinner recipes that are designed to nourish your gut, regulate your blood sugar, reduce inflammation with delicious mediterranean inspired food and cater to the unique needs of those with Hashimoto’s. It will be available shortly. If you want to go on the waitlist just shoot me an email (hello@tessarickardnutritionist.com) and I’ll add you.