Iodine

Tier 2 — promising · Thyroid function · Deficiency

Essential for thyroid hormone production and fetal brain development. WHO estimates deficiency affects over 2 billion people and is the most common preventable cause of intellectual disability. Excess iodine is equally harmful — it can trigger thyroid dysfunction. Test urinary iodine and thyroid panel before supplementing. Iodised salt and seafood are usually sufficient.

Dose: 150–220 mcg/day if deficient; test urinary iodine and thyroid panel first; do not exceed 1,100 mcg/day