Does high-dose IV vitamin C treat cancer or sepsis?

The core issue with oral vitamin C is a bioavailability ceiling. The intestinal absorption of ascorbic acid is tightly regulated by sodium-dependent vitamin C transporters (SVCT1). At oral doses above about 500 mg, absorption efficiency drops sharply, and renal excretion increases. Even at maximum oral dosing, plasma levels peak around 220 micromol/L. By contrast, IV administration bypasses gut absorption entirely and can achieve plasma concentrations of 10,000-20,000 micromol/L — roughly 50-100 times higher¹.

This matters because the biological effects are dose-dependent and qualitatively different at high concentrations:

• Pro-oxidant effect: At pharmacologic concentrations (achievable only via IV), vitamin C generates hydrogen peroxide in extracellular fluid. Cancer cells, which typically have lower catalase activity and higher levels of labile iron, are selectively vulnerable to this oxidative stress. Normal cells can neutralize the peroxide; many cancer cells cannot³.
• HIF-1 alpha suppression: High-dose ascorbate may inhibit hypoxia-inducible factor, which cancer cells rely on for angiogenesis and metabolic adaptation¹.
• Immune modulation: Pharmacologic vitamin C concentrations appear to enhance natural killer cell activity and T-cell function beyond what physiologic levels achieve¹.

The Marik protocol gained widespread attention in 2017 when Dr. Paul Marik published a before-and-after study suggesting that a combination of IV vitamin C, hydrocortisone, and thiamine dramatically reduced mortality in sepsis patients. The CITRIS-ALI trial (a proper randomized controlled trial) tested high-dose IV vitamin C in sepsis with organ failure. The primary endpoint of organ failure scores showed no significant improvement, but 96-hour mortality and ICU length of stay were significantly reduced in the vitamin C group². Subsequent larger trials (VITAMINS, VICTAS) produced mixed results, and the initial enthusiasm has been tempered.

Bowel tolerance dosing is a concept from orthomolecular medicine: you increase oral vitamin C until it causes loose stools, then back off slightly. Proponents claim this threshold rises during illness, reflecting increased tissue demand. While the concept has some logical basis — tissues do consume more vitamin C during infection and oxidative stress — it lacks rigorous clinical validation as a dosing strategy.

Oral vitamin C at higher doses (1-3 grams per day in divided doses) is generally safe for most people. Potential concerns include increased oxalate excretion (relevant for those prone to kidney stones) and interference with certain lab tests¹.

The landmark 2005 NIH study by Chen et al. demonstrated the selective cytotoxicity mechanism that explained why Pauling's oral vitamin C cancer trials failed while his IV-based observations had some merit³. Using pharmacologic concentrations of ascorbate achievable only by IV, they showed that hydrogen peroxide was generated in extracellular fluid at rates sufficient to kill cancer cells while sparing normal cells. This paper essentially restarted serious academic interest in high-dose vitamin C as a cancer therapy after decades of dismissal.

Ohno et al. (2009) reviewed and re-evaluated high-dose vitamin C therapy in cancer treatment¹. They noted that interest among physicians and scientists had grown as research on ascorbate pharmacokinetics and its mechanisms of action against tumor cells was published, and as case studies continued to accumulate suggesting that ascorbate therapy could be effective if the right protocols were used. The authors argued that ascorbate in cancer treatment deserves re-examination.

The CITRIS-ALI trial (Fowler et al., 2019) randomized 167 patients with sepsis and acute respiratory distress syndrome to receive either IV vitamin C (50 mg/kg every 6 hours for 96 hours) or placebo². The primary composite outcome of modified SOFA score change did not differ significantly between groups. However, the vitamin C group showed a significant reduction in 96-hour all-cause mortality (29.8% vs 46.3%, p=0.03) and more ICU-free days. These secondary findings, while provocative, require confirmation in larger trials.