Maximum Daily Iodine Dose for Adults
The tolerable upper intake level (UL) for iodine in adults is 1,100 µg/day according to the US Institute of Medicine, though the European Scientific Committee on Food sets a more conservative limit of 600 µg/day. 1, 2
Upper Limit Guidelines
- The US Institute of Medicine establishes 1,100 µg/day as the tolerable upper limit for adults, above which thyroid dysfunction risks increase significantly 1, 2
- The European Scientific Committee on Food recommends a lower threshold of 600 µg/day as the upper tolerable limit 1
- Intakes exceeding these levels carry high risk for both hypothyroidism and hyperthyroidism 1
Standard Daily Requirements (For Context)
- The recommended daily intake is 150 µg/day for non-pregnant, non-lactating adults 1, 3, 4
- Pregnancy requires 220-250 µg/day depending on the guideline source 1
- Lactation requires 290 µg/day 1
Clinical Manifestations of Excess
Chronic exposure above the upper limits induces several pathological changes:
- Elevated TSH levels with lower thyroid hormone concentrations 5
- Autoimmune thyroiditis (highly iodinated thyroglobulin is more immunogenic) 5
- Hypothyroidism and goiter development 5
- Acute toxicity symptoms include abdominal pain, metallic taste, fever, delirium, diarrhea, and vomiting 5
Critical Nuance: The Wolff-Chaikoff Effect
- Excess iodine temporarily inhibits thyroid hormone synthesis through the Wolff-Chaikoff effect 2, 4
- Most individuals can "escape" this inhibition, but susceptible populations cannot 3, 6
- Vulnerable groups include those with pre-existing thyroid disease, elderly patients, fetuses, neonates, and patients with Hashimoto's thyroiditis 3, 6
Special Populations at Higher Risk
Defective autoregulation occurs in:
- Fetal and neonatal thyroid 6
- Hashimoto's thyroiditis 6
- Post-radioiodine or surgically treated Graves' disease 6
- Longstanding multinodular goiter (may develop Jod-Basedow thyrotoxicosis) 6
Practical Clinical Considerations
- For enteral nutrition, provide 150 µg/day with an upper level of 300 µg per 1500 kcal 5, 7
- In deficiency states, 300-600 µg/day can be given orally or enterally 5
- Common hidden sources of excess iodine include amiodarone, povidone-iodine disinfectants, contrast media, and kelp/seaweed supplements 5, 2, 4
Monitoring Recommendations
- Assess iodine status via 24-hour urinary excretion combined with thyroid function tests (TSH, free T4, T3) and thyroid size 5, 1
- Population median urinary iodine concentration ≥100 µg/L indicates adequate nutrition 1
- During pregnancy, urinary iodine concentration should remain between 150-250 µg/L; exceeding 250 µg/L increases subclinical hypothyroidism risk 1.75-fold 1