Metformin, a prescription diabetes medication, is studied as a candidate for slowing aging. With early blood sugar problems it lowers blood sugar and delays diabetes, though intensive diet and exercise do as well or better. For longer life and fewer heart attacks, cancers or dementia cases, signals come mainly from health-record and animal studies; rigorous trials show no clear advantage. Downsides: digestive upset, vitamin B12 depletion and smaller training gains. (Full Review)
| Marker | Target | Why |
|---|---|---|
| eGFR | ≥45 mL/min/1.73 m² to start; stop below 30 | Safety check: sets eligibility and stop point |
| Vitamin B12 (serum) | >220 pmol/L (about 300 pg/mL) | Safety check: expected to fall |
| Methylmalonic acid (MMA) | <0.4 µmol/L | Safety check: confirms functional B12 deficiency |
| Complete blood count (hemoglobin) | Women 12.0–15.5 g/dL; men 13.5–17.5 g/dL | Safety check: anemia |
| HbA1c | 4.0–5.6% | Expected to change: falls |
| Fasting glucose | 70–99 mg/dL | Expected to change: falls |
| ALT and AST | ALT about 7–56 U/L; AST about 10–40 U/L | Safety check: liver disease rules out use |
| Blood lactate | 0.5–2.2 mmol/L | Safety check: only if acidosis symptoms |
Cadence: Baseline before starting; eGFR at least annually, more often after 65 or with kidney risk; complete blood count annually; vitamin B12 every 2–3 years, sooner if numbness or tingling appears; HbA1c and fasting glucose at 3 months, then every 6–12 months