Folate, an essential B vitamin sold as folic acid or "active" forms, is taken for low intake or age-related problems. Most reliably, it prevents certain birth defects and, in people lacking folate, a specific anemia. For health-focused adults, stroke risk may drop modestly, mostly where foods are not enriched; other benefits are small or disputed. No harm is firmly established; warning signs persist; B12 status shapes benefits and risks. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Serum folate | About 15 ng/mL or higher for carriers of the MTHFR 677 TT gene variant | Expected to change |
| Total homocysteine | 10 µmol/L or below | Expected to change |
| Vitamin B12 (serum) | 200–900 pg/mL | Safety check: low B12 stops high-dose folate |
| Methylmalonic acid (MMA) | About 400 nmol/L or below | Safety check: rising MMA signals masked B12 deficiency |
| Complete blood count with MCV (average red-cell size) | 80–100 fL | Expected to change in deficiency; safety check for B12 |
| eGFR (kidney filtering estimate) | No established target; track change from the individual's own baseline | Safety check in diabetic kidney disease |
| Phenytoin level (users only) | No established target; track change from the individual's own pre-folate level | Safety check: falling levels prompt dose review |
Cadence: Baseline panel before starting; homocysteine, serum folate and vitamin B12 at 8–12 weeks, then every 6–12 months while supplementing; B12 typically yearly with metformin or acid-reducing drugs; kidney function every 6–12 months in diabetic kidney disease; phenytoin levels within 2–4 weeks of any dose change