Selenium for Thyroid Function
In autoimmune thyroiditis (Hashimoto's), selenium reliably lowers thyroid antibody levels over 3 to 6 months, but it does not measurably improve actual thyroid hormone levels, and there is no proof it slows the disease or reduces the need for thyroid medication. The evidence is somewhat better in the separate setting of mild-to-moderate Graves' eye disease.
Why this grade7-layer evidence engine
Selenium earns a Preliminary grade because the benefit is consistent on a surrogate marker but missing on the outcomes that matter clinically. Two meta-analyses in Hashimoto's patients found significant drops in thyroid peroxidase antibodies (TPO-Ab): SMD -0.96 across 2,358 people (PMID 38243784) and a 6-month SMD -0.80 across 1,610 people (PMID 40898469). Crucially, the same analyses showed no significant change in free T4, T4, free T3, T3, or thyroid volume, so the gland's actual function did not improve.
The signal also weakens over time. An umbrella review of prior systematic reviews (PMID 37513612) found the antibody effect was lost by 12 months in people not on levothyroxine, rated overall evidence certainty as very low to low, and noted that progression to clinical hypothyroidism was never tested. Heterogeneity was high, reflecting mixed selenium forms and doses.
Regulators and clinics reinforce this cautious read. EFSA permits only a general 'contributes to normal thyroid function' nutrient claim, not a treatment claim, and the NHS, Mayo Clinic, Cleveland Clinic, and American Thyroid Association do not recommend selenium as a Hashimoto's therapy (the ATA advises against it in pregnancy). The evidence is stronger in mild-to-moderate active Graves' orbitopathy, where selenium improved the Clinical Activity Score and quality of life with effects sustained at 12 months (PMID 39138905); this benefit should not be assumed to carry over to ordinary Hashimoto's. Selenium's safe range is narrow, so intake is generally capped near 200 mcg/day to avoid selenosis.
Scoring transparency
All scores computed by a 7-layer evidence engine — fully auditable▸View the full decision path (audit trail)
- compute_raw_score — 加權公式: L2×0.30 + L3×0.25 + L5×0.25 + L11×0.10 + L1×0.10 = 0.558
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高品質 SR/MA 顯示 positive (2 篇 > 1 negative)
- tier_strict_requirement_check — Tier 條件達標，未降階
- detect_disputes — 偵測到 0 個 hard + 0 個 soft dispute
- decide_status — 依 tier + dispute 結果決定 status