What are the effects of low selenium levels on patients with Hashimoto's (Hashimoto's thyroiditis) disease?

Effects of Low Selenium in Hashimoto's Thyroiditis

Selenium deficiency in Hashimoto's thyroiditis significantly impacts thyroid autoimmunity and should be corrected with supplementation at doses of 100-200 μg/day to reduce antibody levels and improve thyroid function. 1, 2

Impact of Selenium Deficiency in Hashimoto's Thyroiditis

• Increased autoantibody levels: Low selenium status correlates with higher thyroid peroxidase antibody (TPOAb) levels 3, 2
• Impaired thyroid function: Selenium deficiency can worsen thyroid hormone regulation, potentially accelerating progression to overt hypothyroidism 4
• Reduced antioxidant capacity: Selenium is essential for glutathione peroxidase activity, which protects thyroid tissue from oxidative damage 1
• Compromised immune regulation: Deficiency impairs regulatory T cell (Treg) function, particularly activated Tregs, which help control autoimmune responses 5

Diagnostic Considerations

• Plasma selenium measurement: Values <0.75 μmol/L in patients without inflammation indicate need for supplementation 6, 1
• Inflammatory markers: CRP levels affect selenium status interpretation, as inflammation reduces plasma selenium:
  • CRP 10-40 mg/L: 15-25% reduction in plasma selenium
  • CRP 41-80 mg/L: ~35% reduction
  • CRP >80 mg/L: ~50% reduction 6, 1
• Thyroid antibodies: Monitor TPOAb and TgAb as markers of autoimmune activity 2

Supplementation Guidelines

• Recommended dosage: 100-200 μg/day of selenium for patients with Hashimoto's thyroiditis 1, 4
• Form of selenium: Organic forms (selenomethionine) have better bioavailability than inorganic forms 1
• Duration: Minimum 6 months of supplementation to observe clinical effects 4, 2
• Target levels: Aim for plasma selenium ≥1.20 μmol/L for optimal glutathione peroxidase activity 1

Clinical Benefits of Selenium Supplementation

• Reduction in antibody levels: Selenium supplementation significantly decreases TPOAb levels 4, 2
• Improved thyroid function: Can reduce TSH levels in patients without thyroid hormone replacement therapy 2
• Enhanced antioxidant status: Decreases malondialdehyde (MDA), a marker of oxidative stress 2
• Regulatory T cell modulation: Increases percentage of activated Tregs and Helios expression, improving immune regulation 5
• Potential stabilization of disease: May slow progression to overt hypothyroidism 4

Monitoring and Follow-up

• Antibody levels: Check TPOAb every 3 months to assess response 1
• Selenium status: Monitor plasma selenium levels, particularly in long-term supplementation 6, 1
• Thyroid function: Regular assessment of TSH, free T4, and free T3 2
• Safety monitoring: While adverse events are rare at recommended doses, excessive supplementation should be avoided due to potential associations with type 2 diabetes and high-grade prostate cancer 6, 1

Cautions and Considerations

• Selenium toxicity: Upper limits for plasma selenium before toxicity are 6-12 μmol/L 6
• Discontinuation effects: Stopping supplementation may lead to rebound increases in antibody levels 1
• Selenium status variation: Geographic differences in soil selenium content affect baseline status 3
• Concurrent inflammation: Inflammatory conditions require adjusted interpretation of selenium levels 6, 1

Selenium supplementation represents an important adjunctive therapy for patients with Hashimoto's thyroiditis, particularly those with documented deficiency, with strong evidence supporting its role in reducing autoantibodies and potentially improving thyroid function.