Does increasing iodine, selenium, and iron intake help manage hypothyroidism?

Micronutrient Supplementation for Hypothyroidism Management

Increasing iodine, selenium, and iron intake helps manage hypothyroidism only when specific deficiencies of these micronutrients are documented, not as a general therapeutic strategy for all hypothyroid patients. 1

Iodine: Correct Deficiency Only, Avoid Excess

Iodine supplementation is beneficial only in iodine-deficient hypothyroidism and can be harmful in iodine-sufficient populations. 1

• Severe iodine deficiency causes goiter and hypothyroidism because thyroid hormone production requires adequate iodine substrate, even with increased thyroid activity attempting to compensate 1, 2
• The recommended daily iodine intake is 150 mcg/day for adults, with requirements increasing to 220 mcg/day in pregnancy and 290 mcg/day during breastfeeding 1, 3
• Excess iodine intake paradoxically induces autoimmune thyroiditis and can worsen hypothyroidism because highly-iodinated thyroglobulin becomes more immunogenic 4, 5
• Assess iodine status through 24-hour urinary iodine excretion (normal: 100-300 mcg/24hr), not serum TSH, as TSH remains normal despite frank iodine deficiency 1, 3

Critical Caveat for Iodine

Universal salt iodization is the WHO-preferred prevention strategy, but introducing iodine supplementation in previously deficient populations can transiently increase hypothyroidism and thyroid autoimmunity 1, 2. Do not supplement iodine in euthyroid or hypothyroid patients already receiving adequate dietary iodine from iodized salt, seafood, or dairy products 1, 3.

Selenium: Evidence-Based Benefit in Specific Contexts

Selenium supplementation (50-200 mcg/day) reduces thyroid peroxidase antibodies and may improve thyroid function in selenium-deficient patients with autoimmune thyroiditis. 1, 4

• Healthy thyroid function depends on adequate selenium provision at any age, as Type 1 5'-deiodinase (which converts T4 to active T3 in the liver) is a selenoenzyme 1
• Glutathione peroxidases (selenoproteins) protect the thyroid by removing excessive hydrogen peroxide produced during thyroid hormone synthesis 4, 5, 6
• Randomized controlled trials demonstrate that selenium supplementation reduces TPO-antibody titers, hypothyroidism severity, and postpartum thyroiditis in selenium-deficient populations 4, 5
• Daily selenium requirements for patients receiving enteral nutrition are 50-150 mcg, with higher requirements (150-200 mcg) in parenteral nutrition patients with increased losses 1

Critical Selenium-Iodine Interaction

In regions of combined severe iodine and selenium deficiency, normalize iodine supply before initiating selenium supplementation to prevent precipitating hypothyroidism. 6 Combined selenium and iodine deficiency can lead to myxedematous cretinism 6.

Iron: Essential for Thyroid Hormone Synthesis

Iron deficiency impairs thyroid hormone metabolism and should be corrected in hypothyroid patients, particularly menstruating women. 1, 4

• Thyroid peroxidase (TPO), the enzyme responsible for thyroid hormone production, is a heme-containing enzyme that becomes active only after binding iron 4, 5, 6
• Iron deficiency blunts the efficacy of iodine supplementation, while iron supplementation improves thyroid hormone synthesis 6
• Autoimmune thyroiditis patients are frequently iron-deficient due to co-morbid autoimmune gastritis (which impairs iron absorption) and celiac disease (which causes iron loss) 4, 5
• Treatment with iron improves thyroid hormone concentrations in anemic women with impaired thyroid function, and combined thyroxine plus iron therapy is more effective than either alone 4
• Daily iron requirements for enteral nutrition are 18-30 mg, with standard parenteral nutrition providing only 1 mg/day (insufficient for deficiency correction) 1

Iron Assessment and Repletion

Check serum ferritin in all hypothyroid patients, especially menstruating women 4. In women with persistent hypothyroid symptoms despite appropriate levothyroxine therapy, restoration of serum ferritin above 100 µg/L ameliorated symptoms in two-thirds of cases 5.

Practical Algorithm for Micronutrient Management

1. Assess baseline status before supplementation: 24-hour urinary iodine, serum selenium (if available), serum ferritin, and complete thyroid function tests (TSH, free T4, free T3) 1, 3

2. Supplement only documented deficiencies:

   • Iodine: Only if urinary iodine <100 mcg/24hr 1
   • Selenium: 50-100 mcg/day in deficient patients or regions of low selenium intake 4
   • Iron: Correct to ferritin >100 µg/L in symptomatic patients 5

3. Avoid indiscriminate supplementation in iodine-sufficient populations, as excess iodine worsens autoimmune thyroiditis 4, 5

4. Monitor for non-dietary iodine sources including iodinated contrast agents, povidone-iodine disinfectants, and amiodarone, which can deliver massive iodine loads 3