Have you ever wondered why you still feel off even when your thyroid test results are “normal”?

It might be because the thyroid doesn’t work alone—it’s closely connected to your gut and liver.

In this post, we’ll explore how these three systems interact and why taking care of all three is crucial for optimal thyroid health. Whether you’re dealing with unexplained symptoms or just looking to optimize your health, this information is essential.

Liver – Gut – Thyroid Connection

If we want better thyroid function, then we also need to optimize the liver and the gut. Here’s why:

Thyroid & Gut: Thyroid hormones play a role in gut motility, which means they help your digestive system move food along. When your thyroid is underactive, it can cause constipation. On the flip side, gut issues like dysbiosis or inflammation can increase oxidative stress, which may harm your thyroid.

 Thyroid & Liver: Your thyroid hormones also influence how your liver handles fat. If your thyroid is underactive, it could lead to issues like insulin resistance and fatty liver. Additionally, the conversion of T4 (the inactive thyroid hormone) to T3 (the active form) happens primarily in the liver. If your liver isn’t functioning well, your thyroid function could suffer too.

It’s clear that poor thyroid function can negatively impact your gut and liver—and the reverse is also true.

5 Ways to Support Conversion of T4 to T3

For anyone looking to optimize their thyroid function, this is ESSENTIAL.

Your thyroid gland makes hormones in the form of T4, which is then converted into the more active T3 in other areas—especially the liver. If this conversion is sluggish, you may feel the effects of low thyroid function even if T4 levels are within the normal range.

Here are some ways to support the conversion:

Liver Support
Since conversion of T4 to T3 happens primarily in the liver, supporting healthy liver function also supports healthy thyroid function.

Gut Support
The enzyme needed to convert T4 to T3 is also present in the gut wall, so gut health may influence T3 levels.

Nutrient Optimization
T4 to T3 conversion depends on selenium and zinc, found mainly in meats, nuts, and seeds.

Stress Management
Anything the body perceives as stress triggers the release of cortisol. Higher levels of cortisol are associated with more conversion of T4 to reverse T3 (inactive form) rather than the active T3.

Blood Sugar Balance
Similar to the effect of stress, insulin resistance is associated with more conversion of T4 to reverse T3 (inactive form) rather than the active T3.

Other Hormones that affect our Thyroid 

The thyroid is part of the larger endocrine system—which includes hormones produced in the brain, adrenals, ovaries, and pancreas too.

Here are 3 hormones that influence (and are influenced by) the thyroid:

Insulin
Both overactive and underactive thyroid can disrupt glucose metabolism and contribute to insulin resistance. The reverse is also true, with insulin resistance being associated with conversion of T4 to reverse T3 (inactive thyroid hormone) rather than active T3.

Cortisol
Underactive thyroid contributes to higher cortisol levels (a stress hormone) because of reduced cortisol clearance. Also, high levels of cortisol are associated with reduced T4 production and higher levels of reverse T3 (inactive thyroid hormone).

Estrogen
The hormone cascades connecting the brain to the thyroid and the brain to the ovaries work together. Both overactive and underactive thyroid can disrupt the menstrual cycle and lead to irregular periods or fertility challenges.

It’s because of these connections that it’s so important to take a holistic approach when optimizing thyroid function.

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References:

1. Fenneman AC, Bruinstroop E, Nieuwdorp M, van der Spek AH, Boelen A. A Comprehensive Review of Thyroid Hormone Metabolism in the Gut and Its Clinical Implications. Thyroid : Official Journal of the American Thyroid Association. 2023;33(1):32-44. doi:10.1089/thy.2022.0491.

2. Piantanida E, Ippolito S, Gallo D, et al. The Interplay Between Thyroid and Liver: Implications for Clinical Practice. Journal of Endocrinological Investigation. 2020;43(7):885-899. doi:10.1007/s40618-020-01208-6. 

3. Shulhai AM, Rotondo R, Petraroli M, et al. The Role of Nutrition on Thyroid Function. Nutrients. 2024;16(15):2496. doi:10.3390/nu16152496. 

4. Knezevic J, Starchl C, Tmava Berisha A, Amrein K. Thyroid-Gut-Axis: How Does the Microbiota Influence Thyroid Function?. Nutrients. 2020;12(6):E1769. doi:10.3390/nu12061769. 

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Disclaimer:

This information is for educational purposes only and is not intended as medical advice. Consult a qualified healthcare professional before making any health-related decisions. Individual results may vary.