Iodine Supplementation in Hypothyroidism

Diagnostic Algorithm: Determine if Iodine Deficiency is the Cause

• The American College of Nutrition recommends measuring 24-hour urinary iodine excretion (normal: 100-300 mcg/24hr) combined with TSH, free T4, and thyroid antibodies (TPO, thyroglobulin antibodies) to determine if iodine deficiency is the cause of hypothyroidism 3

When to Supplement: Iodine-Deficient Hypothyroidism

• The Clinical Nutrition society recommends providing 150 mcg iodine daily through supplementation or dietary sources (iodized salt at 60 mcg/g, dairy, seafood) if urinary iodine is low (<100 mcg/24hr) and thyroid antibodies are negative 1, 3
• The Clinical Nutrition society also recommends standard iodide delivery of 131 mcg/24hr as part of multi-element mixtures for parenteral nutrition patients 1

When NOT to Supplement: Non-Deficient Hypothyroidism

• The Clinical Nutrition society advises against supplementing iodine for hypothyroidism treatment in iodine-sufficient populations (urinary iodine >100 mcg/24hr), as excess iodine induces hypothyroidism by triggering thyroid autoimmunity, increasing TSH, lowering thyroid hormone levels, and worsening goiter 1, 2, 4

Critical Pitfalls and Special Populations

• The Clinical Nutrition society recommends mandatory supplementation of 150 mcg iodine daily for pregnant and lactating women in iodine-deficient regions 1
• The Clinical Nutrition society advises being vigilant about hidden iodine exposure from iodinated contrast agents, topical povidone-iodine disinfectants, and amiodarone, which can deliver massive iodine loads that induce hypothyroidism 1, 2, 4