Selenium, an essential mineral in foods and dietary supplements, helps the body make protective enzymes and active thyroid hormone. People with low intake appear to gain from reaching adequate levels; those with enough gain little and may face added risks. Clearest benefits are thyroid-related; large trials show no cancer, heart disease, or dementia prevention in adequately nourished adults. For health-focused adults, gain depends on measured status, not routine use. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Plasma or serum selenium | 110–125 µg/L | Confirms need, flags excess |
| HbA1c | 4.0–5.6%; track change from own baseline | A rise signals the diabetes risk and changes use |
| TSH | 0.4–4.0 mIU/L | Falls slightly with selenium; safety check in thyroid disease |
| Thyroid peroxidase antibodies | Below about 35 IU/mL, assay-dependent; track change from own baseline | Expected to change in autoimmune thyroiditis |
| Blood pressure (home average) | No established target for this purpose; track change from own baseline | A systolic rise changes use |
| PSA (men) | 0–4.0 ng/mL; track change from own baseline | A rising value prompts stopping and evaluation |
Cadence: Baseline before starting; plasma selenium and TSH at 3 months, then every 6–12 months; HbA1c and PSA every 12 months; home blood pressure every 3 months; thyroid antibodies at 3–6 months when relevant