Iodine

What It Is

Iodine is a trace mineral and essential micronutrient that the body requires in very small amounts but cannot produce on its own. It is naturally present in some foods, added to others (such as iodized salt), and available as a dietary supplement. Chemically, iodine is a halogen element (atomic number 53) found in the periodic table. In the human body, it primarily exists in the form of iodide (I⁻), a soluble ion that is easily absorbed and transported in the bloodstream.

How It Works

Iodine’s most critical biological role is in the synthesis of thyroid hormones — thyroxine (T₄) and triiodothyronine (T₃). These hormones are produced by the thyroid gland and regulate metabolism, growth, energy production, and development.

Absorption and Transport:

• Dietary iodine is absorbed mainly in the small intestine as iodide. It circulates in the bloodstream and is actively taken up by the thyroid gland through a specialized transporter called the sodium-iodide symporter (NIS).

Thyroid Hormone Production:

Inside the thyroid gland, iodide is oxidized and attached to the amino acid tyrosine, forming monoiodotyrosine (MIT) and diiodotyrosine (DIT). These molecules are then combined to form T₃ and T₄.

• T₃ (Triiodothyronine): Contains three iodine atoms.
• T₄ (Thyroxine): Contains four iodine atoms and is the main circulating form.

Hormone Regulation:

• The release of T₃ and T₄ is controlled by thyroid-stimulating hormone (TSH) from the pituitary gland. When iodine levels are low, the thyroid works harder, often enlarging (goiter formation), to capture more iodine.

Metabolic Effects:

• Once released, T₃ and T₄ enter body cells and influence how energy is generated, how proteins are synthesized, and how sensitive the body is to other hormones.

Why It’s Important

Iodine is vital for proper thyroid function, and by extension, it affects nearly every system in the body:

1. Metabolic Regulation: Adequate iodine ensures that the thyroid produces enough hormones to regulate metabolism, body temperature, and energy balance.
2. Growth and Development: Iodine is crucial during pregnancy, infancy, and childhood. Thyroid hormones support brain and nervous system development, and deficiency during these stages can lead to intellectual disabilities and developmental delays (a condition known as cretinism in severe cases).
3. Cognitive Function:Even mild iodine deficiency can reduce cognitive performance, concentration, and energy levels in adults and children.
4. Hormonal Balance: Iodine helps maintain hormonal stability by preventing thyroid disorders such as hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid).
5. Immune and Reproductive Health: Adequate iodine supports immune function, healthy skin, and reproductive health, and may have antioxidant properties that help neutralize free radicals.

Considerations

While iodine is essential, both deficiency and excess can cause health problems. Here are the key considerations:

Deficiency:

• Common in regions where soil iodine levels are low (e.g., mountainous or inland areas).
• Symptoms include goiter, fatigue, weight gain, cold intolerance, dry skin, hair loss, and mental sluggishness.
• In pregnant women, deficiency can lead to miscarriage, stillbirth, or low IQ in offspring.

Excess Intake:

• Overconsumption (from supplements or seaweed) can also disrupt thyroid function, leading to either hyperthyroidism or hypothyroidism, depending on individual sensitivity.
• Very high levels may trigger thyroid inflammation or autoimmune thyroiditis.

Recommended Intake:

• The Recommended Dietary Allowance (RDA) for adults is approximately 150 micrograms (µg) per day.
• Needs increase to 220 µg during pregnancy and 290 µg during lactation.

Dietary Sources:

• Natural sources include seaweed (kelp, nori), seafood, dairy products, and eggs.
• Iodized salt remains the most common public health intervention to prevent deficiency.

Special Populations:

• Pregnant and breastfeeding women, vegetarians, and people avoiding iodized salt may need supplementation under medical guidance.
• Individuals with thyroid disorders or on medications (like amiodarone) should monitor iodine intake closely.