Riboflavin, or vitamin B2, is a water-soluble vitamin found in dairy and organ meats and sold as a supplement. Functional testing suggests many unsupplemented women and teenagers in wealthy countries fall short. High doses have one well-supported use: preventing migraine attacks. A gene variant may make a low dose lower blood pressure, though that finding is genuinely open. Excess is excreted; the worst common effect is vivid yellow urine. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Erythrocyte glutathione reductase activation coefficient | Below 1.20; 1.20–1.39 suboptimal; 1.40 and above deficient | Only functional test of riboflavin status |
| Plasma or serum riboflavin | 4–24 nmol/L, upper half | Recent intake; confirms adherence |
| Homocysteine | Below 8 µmol/L | Folate–riboflavin pathway readout; main target in the TT genotype |
| MTHFR C677T genotype | No range applies — one-time result of CC, CT or TT | Identifies likely responders to 1.6 mg daily |
| Hemoglobin with mean corpuscular volume | Above 13.5 g/dL men, 12.5 g/dL women | Detects the normocytic anemia of poor riboflavin status |
| Ferritin | 50–150 ng/mL | Stored-iron mobilization depends on riboflavin |
| Home blood pressure, seated average | Below 130/80 mmHg | Primary measurable endpoint in TT homozygotes |
Cadence: Activation coefficient and homocysteine at 12–16 weeks, then annually once stable; home blood pressure twice daily for eight weeks in TT homozygotes on antihypertensives; migraine diary at three months.