Iodine deficiency
A shortage of dietary iodine, the raw material the thyroid needs to make its hormones. It is the world's leading preventable cause of goitre and an underactive thyroid, and in pregnancy it can harm the baby's brain development. Salt iodisation has reduced it, but mild deficiency persists.
What it is
Iodine deficiency occurs when the diet does not supply enough iodine for the thyroid to make adequate amounts of its hormones (T4 and T3), which regulate metabolism, growth and brain development. Iodine comes from iodised salt, dairy, seafood, eggs and some vegetables, and how much is in food depends heavily on soil and farming practices. When intake is low, the thyroid tries to compensate by enlarging — producing a goitre — and driving up TSH; if deficiency is severe or prolonged, hormone production falls and hypothyroidism develops. The consequences depend on life stage. It is by far most important in pregnancy and early life: even mild-to-moderate maternal iodine deficiency can impair the baby's brain development, and severe deficiency causes serious, permanent problems — historically the leading preventable cause of intellectual disability worldwide. In children and adults it causes goitre, hypothyroidism and its symptoms. Universal salt iodisation has dramatically reduced severe deficiency across much of the world, but mild deficiency remains common, including among pregnant women and people who avoid dairy, seafood and iodised salt. Iodine status is judged at population level from urinary iodine, and in individuals through thyroid function and the clinical picture; deficiency is corrected by improving dietary iodine or supplementing, particularly in pregnancy.
Key lab markers
- Urinary iodine — low; the standard population measure of iodine intake (variable in individuals).
- TSH — may be raised as the thyroid is driven to compensate.
- Free T4 — can fall if deficiency is significant, indicating hypothyroidism.
- Thyroglobulin — tends to rise with iodine deficiency and thyroid enlargement.
- Thyroid ultrasound / goitre assessment — for the enlarged gland.
Symptoms
- A goitre (visible or palpable swelling at the front of the neck)
- Symptoms of an underactive thyroid — tiredness, cold intolerance, weight gain, dry skin, constipation
- In pregnancy — risks to the baby's brain development (often without symptoms in the mother)
- In children — impaired growth and development if severe
- Often no symptoms at all in mild deficiency
Related lab panels
When to discuss with a doctor
Iodine deficiency matters most around pregnancy: adequate iodine is important for the developing baby's brain, and many guidelines advise women who are pregnant, breastfeeding or planning pregnancy to ensure sufficient iodine, often with a supplement — so it is worth discussing with your doctor at that stage. Outside pregnancy, iodine deficiency is considered when there is a goitre or an underactive thyroid, as part of assessing the cause. Because both too little and too much iodine can disturb the thyroid, changes to iodine intake are best guided rather than self-directed. Mediora.AI can show a urinary iodine result alongside thyroid function (TSH, free T4) and thyroglobulin so the pattern is read together; interpreting it and deciding on any supplement, especially in pregnancy, belongs with your doctor.