t4 to t3

Conversion of t4 to t3 thyroid hormone

Do you have a thyroid disorder? Or rather, do you suspect you have a thyroid disorder, yet your blood work came back “normal”?

Testing only TSH to assess thyroid function is not enough. 

During a comprehensive thyroid workup, we assess how well your body is converting the main thyroid hormone (T4) to the active thyroid hormone (T3). Your T4 hormone must be converted into T3 in order for your body to use it.This article will review the conversion of T4 to T3 and what you can do to optimize it!

Why Does Conversion of T4 to T3 Matter?

Traditional health practitioners screen thyroid function by looking at one main lab value called thyroid stimulating hormone (TSH).

The pituitary gland in your brain releases TSH which then tells your thyroid gland to make thyroid hormone (abbreviated T4).

However, your body must convert T4 into T3 (the active form) in order to use it. If the conversion of T4 to T3 is poor, then you may experience some of the common hypothyroid symptoms like fatigue, depression, sensitivity to cold temperatures, difficulty concentrating, and more.

Keep in mind, that this poor conversion can occur even if your TSH levels appear to be normal. So, it’s important to assess the conversion of T4 to the active form of T3 to find the root cause of your symptoms and optimize thyroid function.
thyroid hormone conversion

What hurts the conversion of T4 to T3?

Many factors hinder your body’s conversion of T4 to the active T3 form. Let’s review a few of the main ones!


No surprise here, right? 

In times of chronic stress, your body releases higher amounts of a stress hormone called cortisol. At this time, your body is focused on the cortisol release, so it does not put much effort into converting T4 into T3. Instead, it redirects T4 to another hormone called reverse T3 (1).

Your body requires a delicate balance of reverse T3. Too much of this hormone as a result of chronic stress can slow metabolism and cause other detrimental effects in the body. 

Impaired Liver Function

Your thyroid gland makes T4 and a tiny bit of T3. 

However, most conversion of T4 to T3 occurs outside of the thyroid gland, particularly in the liver (2). Impaired liver function, therefore, may negatively affect this conversion even if liver enzymes appear to be within normal limits.

Poor Gut Health 

Your gut is another location where the conversion of T4 to T3 occurs. Disruptions in gut health as seen in dysbiosis (an imbalance of gut bacteria), inflammatory bowel disease, or leaky gut may reduce your body’s ability to convert T4 into the active T3 hormone. 

Low-Calorie Diets

Low-calorie diets can be damaging to thyroid function and may reduce T3 concentrations by up to 50 percent (3). 

When you severely restrict calories, your body will redirect your thyroid hormone (T4) into the reverse T3 version, which causes a drop in your metabolism (4). This is a protective mechanism to prolong your survival in times of famine and food restriction. 

What helps the conversion of T4 to T3?

Fortunately, there are many diet and lifestyle interventions that can optimize your conversion of T4 to T3. 

Follow an Anti-Inflammatory Diet

Poor conversion of T4 to T3 often boils down to chronic inflammation. 

To help lower inflammation, follow an anti-inflammatory diet that is rich in fruits, veggies, wild-caught fish, nuts, seeds, and legumes. Limit foods that may worsen inflammation like refined grains, processed foods, alcohol, and added sugar. 

Remember to eat enough calories, too!

Eat Enough Zinc and Selenium 

Zinc and selenium are two essential minerals required for the conversion of T4 to T3. In fact, one of the main enzymes that makes this conversion relies on selenium in order to function!

Eat plenty of foods rich in these two essential minerals:
  • Foods rich in zinc: oysters, beef, crab, pumpkin seeds, cashews, and chickpeas
  • Foods rich in selenium: brazil nuts, tuna, halibut, sardines, turkey, and beef liver

Root Thyroid Support 

Root Thyroid Support supplement includes important nutrients, liver support, and stress support to optimize T4 to T3 conversion.

Lower Stress Levels

Managing stress is key to lowering cortisol levels and optimizing the T4 to T3 conversion. Are there any stressors in your life that you can reduce or eliminate?

Make time for a daily stress reducing activity like yoga, meditation, journaling, walking, or deep breathing exercises.
Ashwagandha is a common supplement used for stress support that has also been shown in studies to improve levels of T4 and T3 thyroid hormones. (5) 
thyroid support supplement

Thyroid Support

The perfect synergy of nutrients for thyroid health.


Feel calm & relaxed with this powerful adaptogenic herb

Optimize Gut Health

The gut plays an integral role in lowering inflammation and helping your body convert T4 to T3.
Optimizing gut health begins with a solid foundation of an anti-inflammatory diet rich in fiber and low in processed foods.  However, some people require a more comprehensive plan to treat gut imbalances.
We take a personalized approach to gut health and can test for potential gut irritants such as food sensitivities, infections, or bacterial overgrowth. From there, we guide you in replacing missing elements (like digestive enzymes), repopulating the gut with friendly gut bacteria, and repairing the gut lining. 

Finding the Root Cause of Thyroid Issues

Trying to navigate health issues on your own can be overwhelming and frustrating. When it comes to optimizing the conversion of T4 to T3 and treating thyroid conditions, finding the root cause is essential.
Whether it’s poor gut health, nutrient deficiencies, or inflammation, we are here to support and guide you in your healing journey.

Learn more about Root Membership.  

Get to the Root at Home 

Curious about where you should start your functional medicine journey? 

Take our Get to the Root Quiz so you can start working towards reversing disease and optimizing your health at the Root cause.
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