Iodine
Iodine is an essential dietary mineral required by the thyroid gland to synthesise thyroxine (T4) and triiodothyronine (T3). It is particularly critical during pregnancy for fetal brain development.
Dietary Sources
- Seaweed and kelp (very high)
- Fish and shellfish
- Iodized table salt
- Dairy products
- Egg yolks
- Fortified foods
Iodine and Hyperthyroidism
- In people with a normally functioning thyroid, adequate iodine intake is essential and may even reduce the risk of developing hyperthyroidism (2019 Danish study).
- In people with autoimmune hyperthyroidism (especially graves-disease), excess iodine worsens symptoms by stimulating further thyroid hormone production. Doctors typically advise lowering (not completely eliminating) iodine intake.
- iodine-induced-hyperthyroidism (IIH): Caused by excessive iodine intake from supplements, high-iodine foods, iodine contrast dyes, or certain medications (cough syrups). Usually temporary; may require dietary changes or medical intervention, especially if thyroid nodules develop.
- Correction of iodine deficiency can paradoxically trigger transient hyperthyroidism in previously deficient individuals.
- For patients on antithyroid drugs, taking extra iodine can counteract the medication’s benefits.
Iodine and Hypothyroidism / Levothyroxine
- Patients taking levothyroxine for hypothyroidism do not need iodine supplements.
- Iodine supplementation is unnecessary and potentially harmful in patients being treated for hyperthyroidism.
Low-Iodine Diet
See: low-iodine-diet — prescribed before radioactive-iodine-treatment to maximise uptake of the therapeutic dose.
Recommended Intake
- Adults: ~150 mcg/day (sufficient from a balanced diet in iodine-replete countries)
- Pregnant women: higher requirements; supplementation may be needed
- Low-iodine diet threshold: <50 mcg/day (pre-treatment protocol)