Selenium Supplementation for Hypothyroidism
For patients with hypothyroidism, selenium supplementation at 100 μg/day is the recommended starting dose, though routine supplementation is not warranted in selenium-replete populations without documented deficiency.
When to Consider Selenium Supplementation
Selenium supplementation should be reserved for patients with documented selenium deficiency (plasma selenium <0.75 μmol/L or <59 μg/L) or those with autoimmune thyroiditis (Hashimoto's) and subclinical hypothyroidism. 1
Testing Before Supplementation
- Measure plasma selenium levels before initiating supplementation, particularly in patients with risk factors including malabsorption disorders, long-term enteral nutrition, or autoimmune thyroid disease 1
- Always measure CRP simultaneously, as inflammation significantly reduces plasma selenium levels (15-50% reduction depending on CRP elevation) 1, 2
- Target plasma selenium concentration is ≥0.75 μmol/L (≥59 μg/L) in patients without inflammation 1
- Values <0.4 μmol/L (<32 μg/L) always warrant supplementation 2, 3
Dosing Recommendations
Standard Dosing for Mild Deficiency
- Start with 100 μg/day for patients with mild selenium deficiency or autoimmune thyroiditis 1
- This dose can be given as selenomethionine orally 4
- Continue for at least 4-6 months before reassessing 4
Higher Doses for Significant Deficiency
- For plasma selenium <0.4 μmol/L, consider up to 400 μg/day for 7-10 days for rapid correction, then reduce to maintenance dosing 1, 2
- Patients with proven recent deficiency may require up to 200 μg/day with monitoring 2
Specific Clinical Context: Autoimmune Thyroiditis
- In subclinical hypothyroidism with autoimmune thyroiditis (TSH <10 mU/L), 83 μg/day selenomethionine for 4 months restored euthyroidism in 31% of patients 4
- Selenium supplementation consistently reduces TPOAb levels (thyroid peroxidase antibodies) regardless of thyroid hormone replacement status 5
Evidence for Efficacy
The most recent high-quality meta-analysis demonstrates:
- Selenium supplementation modestly decreases TSH in patients without thyroid hormone replacement (SMD -0.21) 5
- Significant reduction in TPOAb levels (SMD -0.96) 5
- Reduction in oxidative stress markers (MDA) 5
- However, in selenium-replete populations, supplementation causes only minute decreases in TSH and FT4 without clinical benefit 6
Critical Pitfalls and Warnings
Do Not Supplement Routinely
- Selenium supplementation is NOT warranted in selenium-replete populations with marginal deficiency 6
- In euthyroid subjects with adequate selenium intake, supplementation does not improve thyroid function and may cause unnecessary TSH/FT4 suppression 7, 6
Toxicity Concerns
- Upper toxicity limits occur at plasma selenium levels of 6-12 μmol/L 1, 2
- Selenosis manifests as headache, hair and nail loss, skin rash, and neurological symptoms 1
- Chronic overexposure is associated with type 2 diabetes and high-grade prostate cancer 2, 3
- Never use high-dose selenium (1000-4000 μg/day) as seen in some ICU protocols—this is explicitly not recommended and shows no benefit 2, 3
Maximum Safe Dose
- Do not exceed 400 μg/day except for short-term (7-10 days) correction of severe deficiency 1, 2
- Typical supplementation should remain at 100-200 μg/day 1, 2
Monitoring Strategy
- Recheck plasma selenium and CRP after 3-6 months of supplementation 3
- Monitor thyroid function (TSH, FT4) at 6-8 weeks if patient is on thyroid hormone replacement 8
- For patients with autoimmune thyroiditis, consider monitoring TPOAb levels to assess response 5
Special Populations
Graves' Disease/Thyroid Eye Disease
- For mild thyroid eye disease, selenium 100 μg/day may reduce inflammatory symptoms 1
- Selenium does not impact control of hyperthyroidism in non-deficient populations 1