🧬 Family & Essentiality

🌿 Plain-Language Summary

Iodine is essential for making thyroid hormones (T4 and T3), which regulate growth, brain development, and metabolism. In Australia, iodised salt and bread (manufactured with iodised salt) are key contributors to population iodine intake. Specialty salts (e.g., Himalayan, sea salt) are often not iodised.

⚗️ Molecular & Chemical IDs

• Element: I (Iodine)
• Atomic number: 53
• Dietary forms: iodide (common), iodate (converted to iodide in the gut)

⚡ Functions

• Thyroid hormone synthesis (T4 thyroxine, T3 triiodothyronine)
• Critical for foetal and infant neurodevelopment
• Maintains basal metabolic rate and growth

🍽️ Absorption & Bioavailability

🥗 Food Sources

• Seafood (fish, seaweed — variable content)
• Dairy and eggs (due to feed and sanitation iodine use)
• Bread (iodised salt mandatory in Australia)
• Iodised table salt

🇦🇺 Australian NRVs (NHMRC)

• RDI (Adults): 150 µg/day
• Pregnancy: 220 µg/day
• Lactation: 270 µg/day
• UL (Adults): 1100 µg/day

🚨 Deficiency & Excess

Deficiency

Causes goitre (thyroid enlargement), hypothyroidism, and in pregnancy can impair foetal neurodevelopment. Historically common in Australia before iodisation programs.

Excess

Very high intakes can trigger thyroid dysfunction (hypo- or hyperthyroidism) in susceptible individuals. Excess often arises from seaweed consumption or inappropriate supplementation.

🧪 Testing & Monitoring

• Population status: Urinary iodine concentration (UIC)
• Individuals: Thyroid function tests (TSH, free T4) + diet history
• Direct iodine tests are less reliable than thyroid hormone measures

🔄 Interactions

• Thyroid medications (e.g., levothyroxine) require consistent iodine intake
• High seaweed or supplement intake can provide excessive iodine
• Goitrogens from some plant foods may impair iodine use if intake is already low

📊 Evidence Snapshot

• 🔬✅ Well-established: Iodine prevents goitre and supports neurodevelopment
• ⚠️ Clinical caution: Excess intake can disrupt thyroid function, especially in older adults or those with thyroid disease