Should patients with hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid) take selenium supplements?

Selenium Supplementation in Thyroid Disorders

Selenium supplementation is beneficial for patients with mild to moderate Graves' orbitopathy (thyroid eye disease), but has not shown significant benefits for patients with hypothyroidism or hyperthyroidism in selenium-sufficient populations. 1, 2

Selenium and Thyroid Function

Selenium is an essential micronutrient with high concentration in the thyroid gland. It plays crucial roles in:

• Thyroid hormone metabolism
• Antioxidant function through selenoproteins
• Protection against oxidative stress

Evidence-Based Recommendations for Different Thyroid Conditions

For Graves' Orbitopathy (Thyroid Eye Disease)

• Selenium supplementation has demonstrated clear benefits in mild to moderate thyroid eye disease:
  • Reduces inflammatory symptoms 1
  • Improves quality of life 1
  • Delays progression of ocular disorders 1
  • Works primarily through antioxidant effects 1

For Hyperthyroidism (Graves' Disease)

• Current evidence does not support routine selenium supplementation:
  • No significant improvement in short-term control of hyperthyroidism when added to methimazole treatment 3
  • Does not impact control of hyperthyroidism in selenium-sufficient populations 1
  • May potentially be beneficial in selenium-deficient areas, but evidence is limited 3

For Hypothyroidism (Including Hashimoto's Thyroiditis)

• Evidence for selenium supplementation in hypothyroidism shows:
  • May reduce anti-thyroid peroxidase antibody levels in autoimmune thyroiditis 2
  • May improve thyroid ultrasound features in autoimmune thyroiditis 2
  • Does not significantly affect the conversion of T4 to T3 in patients with congenital hypothyroidism 4

Formulation and Dosing

• Organic forms of selenium (such as selenomethionine) appear to be more effective than inorganic forms 2
• Typical dosing in clinical studies:
  • 100-200 μg daily for Graves' orbitopathy 1
  • 20-60 μg daily has been studied in congenital hypothyroidism 4

Clinical Considerations and Monitoring

When to Check Selenium Levels

• Consider checking selenium levels in:
  • Patients with chronic diarrhea
  • Metabolic bone disease
  • Unexplained anemia
  • Unexplained cardiomyopathy 1
  • Patients with mild to moderate Graves' orbitopathy 1

Potential Pitfalls and Caveats

1. Selenium toxicity can occur with excessive supplementation
2. Selenium supplementation may affect thyroid function tests in euthyroid individuals with marginal selenium deficiency 1
3. Geographic variations in soil selenium content affect baseline selenium status
4. Selenium supplementation should be considered in the context of the patient's overall selenium status

Conclusion

For clinical practice, the evidence supports selenium supplementation primarily for patients with mild to moderate Graves' orbitopathy. There is insufficient evidence to recommend routine selenium supplementation for patients with uncomplicated hypothyroidism or hyperthyroidism, particularly in selenium-sufficient populations.