Thyroid Gland: Synthesis of T4 and T3, the Role of Iodine and Selenium

The thyroid gland weighs grams but manages the energy of the whole body. Its hormones — T4 and T3 — regulate metabolism, temperature and heartbeat. And their synthesis needs two "ingredients": iodine and selenium. Let's look at how this works.

🔬 What the gland does

The thyroid gland is the "conductor" of metabolism. Its hormones affect metabolic rate, energy, weight, mood and even heartbeat.

• Regulates metabolism.
• Affects energy.
• Affects weight.
• Affects mood.

🧪 T4 and T3

The gland produces T4 (thyroxine) and T3 (triiodothyronine). T4 is the "reserve," and active T3 gives energy. Most T3 is made from T4 in tissues.

• T4 — "reserve."
• T3 — active.
• T3 from T4 in tissues.
• Give energy.

🦠 Iodine

Iodine is the "building material" of the hormones. Without it, the gland can't synthesize T4 and T3. Its lack is a main cause of disorders.

• Building material.
• For T4 and T3.
• Lack — risk.
• Key mineral.

🟡 Selenium

Selenium helps convert T4 into active T3 and protects the gland from oxidative stress. It's the "helper" of iodine.

• Converts T4 to T3.
• Protects the gland.
• Iodine helper.
• Antioxidant.

⚠️ Signs of disorders

• Fatigue and weakness.
• Weight changes.
• Sensitivity to cold.
• Mood problems.
• Dry skin and hair.

🥗 Food sources

💡 Practice

• Eat fish and seafood.
• Brazil nut — 1–2 a day.
• Iodized salt.
• Check TSH, T4, T3.
• Don't take iodine in high doses.
• Consult a doctor.