Key Takeaway
NIH study showing oral vitamin C saturates at ~200mg doses, while higher oral doses are poorly absorbed - explaining why IV vitamin C achieves much higher blood levels.
Summary
This NIH pharmacokinetic study characterized vitamin C absorption and plasma levels after various oral and IV doses.
Key finding: oral vitamin C absorption is tightly controlled, with plasma levels plateauing around 220 µmol/L even with high oral doses. IV administration bypasses this limit and can achieve much higher concentrations.
Methods
- Pharmacokinetic study
- 7 healthy volunteers
- Doses from 30mg to 2.5g oral
- IV comparison arm
Key Results
- Oral absorption saturates above 200mg
- Maximum oral plasma level ~220 µmol/L
- IV achieves 1000+ µmol/L
- Rapid renal excretion of excess
Limitations
- Small sample size
- Healthy volunteers only
- Single-dose kinetics