Understanding Thyroid Function & Hormone Production

A middle-aged woman sits peacefully on a garden bench with eyes closed, smiling while gently touching her throat, symbolising relief, comfort, and healing with homeopathy for hypothyroidism.

This is Part 2 of our thyroid series, focusing on how the thyroid works and how the body produces its essential hormones.

(If you missed Part 1, which explored the connection between toxic load and thyroid function, you can read it here.)

A Quick Refresher on Thyroid Physiology

When we think about thyroid health, it’s important to go beyond just the gland itself or hormone replacement. The thyroid produces four main hormones — T1, T2, T3, and T4 — each with unique roles. These hormones are built from key nutrients including iodine, selenium, vitamins B1 and B2, and the amino acid tyrosine. Without adequate amounts of these raw materials, the body cannot make sufficient thyroid hormones.

Because iodine deficiency is widespread due to depleted soils, it’s worth checking your levels with an iodine loading test. Include iodine-rich foods like iodised salt, seaweed, fish, eggs, and prunes. Be aware that in the 1970s and 80s, iodine was removed from many grain products and replaced with bromine — which actually blocks iodine absorption. Flame retardants in furniture and vehicles, along with chlorinated or fluoridated water, can also limit iodine uptake. A good water filter can help reduce these effects.

How Thyroid Hormones Work in the Body

T3, the most active thyroid hormone, binds to receptors in your tissues to keep metabolism running smoothly — influencing energy, mood, digestion, and even body temperature. Low T3 levels can result in classic hypothyroid symptoms.

Here’s a simplified breakdown of how the hormones interact:

T4 – The main storage hormone. It’s inactive but acts as a reserve, ready to be converted into T3.
T3 – The active hormone, 4–10 times more powerful than T4, boosting metabolism, energy, and overall vitality.
T2 – Supports the conversion of T4 to T3 and plays a role in fat burning.
T1 – Helps regulate thyroid function and supports heart health.

This explains why relying solely on T4-based medications like Levothyroxine often fails to resolve symptoms. If your body can’t efficiently convert T4 into T3, you may still feel unwell. One major factor in this conversion process is the health of your liver — where most T4 to T3 transformation happens.

The Role of Deiodinase Enzymes

Three key enzymes — D1, D2, and D3 — control the conversion and balance of thyroid hormones:

D1 – Converts T4 to T3 in peripheral tissues but works slowly and is easily disrupted by stress or illness. This can lead to low T3 in the body despite normal thyroid-stimulating hormone (TSH) levels.
D2 – Highly efficient, converting T4 to T3 mainly in the pituitary gland. It regulates most of the body’s T3 production but can give a misleading picture of overall thyroid health if tissue levels remain low.
D3 – Acts as a brake on thyroid activity, converting T4 into reverse T3 (RT3), which reduces T3 availability in tissues.

Why This Matters

Deiodinase activity — along with factors like sleep, stress, inflammation, environmental toxins, and certain medications — is critical for healthy thyroid function. It’s not only about how much hormone you have, but how effectively your body can convert and use it.

If you have hypothyroidism or Hashimoto’s thyroiditis, supporting these enzyme processes and improving liver health can make a significant difference. Lifestyle adjustments, targeted nutrition, and reducing toxin exposure all play a role in helping your thyroid perform at its best.

Originally authored by Dr. Anthony de Pontes, adapted with permission for Homeopathy247.com.

What are the main hormones produced by the thyroid?

The thyroid produces four hormones — T1, T2, T3, and T4. T4 acts as a storage form, T3 is the most active and regulates metabolism, T2 supports T4-to-T3 conversion, and T1 helps regulate thyroid and heart function.

Why is iodine important for thyroid health?

Iodine is a key nutrient needed to make thyroid hormones. Without enough iodine, the body cannot produce sufficient T1, T2, T3, or T4. Good sources include iodised salt, seaweed, fish, eggs, and prune

Why do some people still feel unwell on Levothyroxine (T4) medication?

Levothyroxine provides only T4, the inactive form. If the body struggles to convert T4 into active T3 — often due to poor liver health, stress, or disrupted enzyme activity — symptoms of hypothyroidism may persist.

What are deiodinase enzymes and why are they important?

Deiodinase enzymes (D1, D2, and D3) control thyroid hormone conversion. D1 and D2 convert T4 into active T3, while D3 reduces thyroid activity by turning T4 into reverse T3 (RT3). Their activity is vital for maintaining healthy thyroid balance.

How can I support healthy thyroid hormone conversion naturally?

You can support thyroid health by reducing stress, improving sleep, supporting liver function, eating nutrient-rich foods (especially iodine and selenium), filtering water to reduce toxins, and working with a practitioner to address underlying imbalances.