Role of Selenium Supplementation in Thyroid Disease

Clinical Applications in Specific Thyroid Conditions

Selenium supplementation may delay the progression of ocular disorders in Graves' disease, according to the American Academy of Ophthalmology 1
For mild thyroid eye disease (TED), selenium supplementation has been shown to reduce inflammatory symptoms, as recommended by the European Society of Endocrinology 1, 2

The recommended starting dose is 100 μg/day for patients with mild selenium deficiency, as suggested by the Clinical Nutrition Society 3, 4
For patients with more significant deficiency, higher doses up to 400 μg/day may be required for 7-10 days for rapid correction, according to the Clinical Nutrition Society 3, 5

Plasma selenium levels should be measured to assess deficiency status, ideally along with glutathione peroxidase-3 (GPX-3) to reflect functional status, as recommended by the Clinical Nutrition Society 5

Selenium supplementation does not appear to impact control of hyperthyroidism in populations that are not selenium deficient, according to the American Academy of Ophthalmology 1
There is evidence of potential harm with excessive selenium intake, with upper limits before toxicity symptoms ranging from 6-12 μmol/L, as reported by the Clinical Nutrition Society 3
Selenium toxicity (selenosis) can manifest as headache, hair and nail loss, skin rash, and neurological symptoms, according to the Clinical Nutrition Society 6
High-dose selenium supplementation (1000-4000 μg/day) in ICU patients has not shown consistent benefits and is not recommended, as suggested by the Clinical Nutrition Society 3, 7

Plasma selenium measurement should be obtained if supplementation is being considered or if the patient has clinical features suggesting deficiency, according to Clinical Nutrition guidelines 8
Measure plasma selenium levels in antibody-positive patients who have risk factors for deficiency, including long-term enteral nutrition, malabsorption disorders, burns, major trauma, or continuous renal replacement therapy 8

Target plasma selenium concentration is ≥0.75 μmol/L (≥59 μg/L) in patients without inflammation, as recommended by Clinical Nutrition 8
Values <0.4 μmol/L (<32 μg/L) always warrant supplementation, while values between 0.4-0.75 μmol/L indicate relative deficiency and may benefit from supplementation, particularly in autoimmune thyroid disease 8
Inflammation significantly affects results, with CRP 10-40 mg/L causing 15-25% reduction in plasma selenium, CRP 41-80 mg/L causing ~35% reduction, and CRP >80 mg/L causing ~50% reduction 8
Always measure CRP simultaneously with selenium to interpret results correctly, as suggested by Clinical Nutrition guidelines 8

Consider adding glutathione peroxidase-3 (GPX-3) to reflect functional selenium status and short-term changes, and red cell glutathione peroxidase (GPX-1) for longer-term selenium status assessment over the erythrocyte lifespan 8

Testing is costly when done routinely without clinical indication, with one study showing $13 per patient just for laboratory draws, plus additional staff time 8