HIGH-DOSE VITAMIN C AND ITS ROLE IN CANCER THERAPY
Research Activities Scientific Literature edited by Dr. Adilardi Pasquale
At high concentrations, vitamin C can generate hydrogen peroxide in the tumor microenvironment, which can selectively damage tumor cells (more sensitive to oxidative stress).
Some work suggests that cells with KRAS or BRAF mutations may be particularly vulnerable.
However, these findings do not always translate to humans.
2. Clinical studies on humans
Clinical studies are still relatively few and often with small sample sizes.
a) Intravenous Vitamin C Chemotherapy
Several phase I–II trials suggest that it may:
- reduce side effects of chemotherapy
- improve quality of life
- potentially increase the effectiveness of standard therapies
For example:
- In a study of patients with ovarian cancer, the addition of intravenous vitamin C to chemotherapy reduced the toxicity of therapy.
Studies on pancreatic cancer
Some recent findings indicate possible benefits.
- A phase 2 clinical trial has suggested that adding intravenous vitamin C to chemotherapy may increase survival in patients with advanced pancreatic cancer.
- Other studies are evaluating combinations with standard drugs such as gemcitabine and erlotinib.
- However these studies are still:
- with few patients
- often not definitive
Studies on other tumors
Trials are underway on:
- colon cancer-
- lung cancer
- tumors with KRAS/BRAF mutations
In these studies, very high infusions (up to 1–1.25 g/kg intravenously) are used to evaluate safety and possible tumor response.
1. Preclinical studies (cells and animals)
Many in vitro and animal model studies show antitumor effects.
Proposed mechanism:
· at high concentrations vitamin C can generate hydrogen peroxide in the tumor microenvironment
· this can selectively damage tumor cells (more sensitive to oxidative stress)
Some work suggests that cells with KRAS or BRAF mutations may be particularly vulnerable.
However, these findings do not always translate to humans.
Clinical studies on humans
Clinical studies are still relatively few and often with small sample sizes.
Intravenous Vitamin C Chemotherapy
Several phase I–II trials suggest that it may:
- reduce side effects of chemotherapy
- improve quality of life
potentially increase the effectiveness of standard therapies
For example:
- In a study of patients with ovarian cancer, the addition of intravenous vitamin C to chemotherapy reduced the toxicity of therapy.
Studies on pancreatic cancer
Some recent findings indicate possible benefits.
- A phase 2 clinical trial has suggested that adding intravenous vitamin C to chemotherapy may increase survival in patients with advanced pancreatic cancer.
- Other studies are evaluating combinations with standard drugs such as gemcitabine and erlotinib.
However, these studies are still: with few patients, often not definitive
Studies on other tumors
Trials are underway on:
- colorectal cancer
- lung cancer
- tumors with KRAS/BRAF mutations
In these studies, very high infusions (up to 1–1.25 g/kg intravenously) are used to evaluate safety and possible tumor response.
Oral vs. Intravenous Vitamin C
This is a key point.
- Oral: the body limits absorption → relatively low plasma levels
- Intravenous: blood concentrations up to 100 times higher
For this reason, many antitumor effects observed in studies occur only with IV infusion.
Position of guidelines and scientific reviews
Systematic reviews and cancer societies generally conclude:
- There is no solid evidence that vitamin C alone cures cancer.
- may have potential as an adjuvant therapy (in combination with chemotherapy or radiotherapy)
- Larger, more controlled clinical trials are needed
Furthermore, taking antioxidant supplements has not been shown to prevent cancer in the general population.
Possible risks of high doses
High doses (especially IV) can cause:
- kidney stones
- hemolysis in patients with G6PD deficiency
- interactions with some oncology therapies
For this reason it is only used in clinical protocols or under medical supervision.
Conclusion (current scientific consensus):
- There is promising biological evidence and preliminary clinical studies
- High-dose vitamin C is not a proven cancer therapy
- It could become a complementary treatment in some tumors, but larger trials are needed.
Studio meccanicistico molto citato Science (2015) “Vitamin C selectively kills KRAS and BRAF mutant colorectal cancer cells”
Main result
- High concentrations of vitamin C selectively kill tumor cells with KRAS or BRAF mutations (common in colon cancer).
- the mechanism:
- tumor cells take up dehydroascorbate via GLUT1
- oxidative stress is generated
- the glycolytic enzyme GAPDH is inhibited, causing cellular energy crisis.
Importance
- provided a strong biological basis for clinical trials.
Limit
- Mainly preclinical study (cells animal models). Radiosensitization study - Cancer Research (2015) – highly cited line of research in oncology: "Pharmacological ascorbate radiosensitizes pancreatic cancer." Results
- High-dose ascorbate generates hydrogen peroxide (H₂O₂) which increases oxidative damage in tumor cells.
- combined with radiotherapy:
- reduces the survival of tumor cells
- slows tumor growth in mouse models.
Meaning
- suggests that vitamin C may potentiate radio- and chemotherapy. Phase I clinical trial (IV monotherapy) Cancer Chemotherapy and Pharmacology (2013)
Drawing
- patients with advanced solid tumors
- intravenous infusions up to 70–110 g/m².
Results
- plasma levels up to 49 mM
- well-tolerated therapy
- No objective tumor response in patients. Interpretation: Demonstrates safety and pharmacokinetics, but not efficacy alone.
Phase I–II clinical trial (vitamin C chemotherapy) Integrative oncology clinical trials
- IV vitamin C chemotherapy in patients with advanced tumors.
Results
- safe and well-tolerated treatment
- Some patients showed temporary stabilization of the disease and functional improvement.
Limit
- very small sample (≈14 patients).
Recent clinical trial on pancreas (much discussed)
Redox Biology / randomized trial (2024)
Drawing
· vitamina C EV gemcitabina nab-paclitaxel
· metastatic pancreatic cancer.
Results
- median survival:
- 16 months with vitamin C
- 8.3 months on chemotherapy alone
- no significant increase in toxicity.
Limits
- very small number of patients (~34)
- phase II study → confirmation needed with phase III.
Systematic review of clinical trials - Antioxidants (2018) - Analysis of clinical trials on IV vitamin C:
Main conclusions:
· therapy is generally safe
· evidence of improved quality of life
· antitumor results still inconsistent or preliminary.
Summary of current scientific evidence
Strong evidence
· plausible antitumor molecular mechanisms
· safety of IV ascorbate
· possible synergy with chemotherapy or radiotherapy
Weak evidence
- few large randomized trials
- many studies with:
- few patients
- phase I–II
- exploratory endpoints
Current consensus in oncology
· it is not standard therapy
· can be studied as an adjuvant therapy.
Conclusion: Studies published in high-level journals suggest that pharmacological ascorbate has interesting biological mechanisms and promising preliminary clinical results, but robust phase III trials are still lacking to demonstrate a real clinical benefit.
Five of the most promising clinical trials (2023-2025) investigating high-dose intravenous vitamin C (pharmacological ascorbate) as an adjunctive cancer therapy. These trials are the most cited in recent publications and clinical registries.
1. Randomized trial in metastatic pancreatic cancer (2024) Study: IV vitamin C standard chemotherapy, Drugs: gemcitabine nab-paclitaxel: Phase: II randomized
Main results
- median survival:
- 16 months with vitamin C
- 8.3 months on chemotherapy alone
- disease progression:
- 6.2 months vs 3.9 months
- no significant increase in toxicity.
Published in Redox Biology (2024). It is considered one of the most promising clinical results to date.
2. Trial fase II su glioblastoma
Study: IV vitamin C standard therapy (surgery radiation temozolomide) Registry: NCT02344355 Parent site: University of Iowa
Protocol
- IV infusion 3 times a week during radio-chemo
- then 2 times a week during adjuvant chemotherapy.
Objective:
- improve survival and response to radiotherapy in glioblastoma.
This trial builds on a previous Phase I study that demonstrated the safety of the combination of temozolomide and radiation therapy.
3. Vitamin C Chemoradiotherapy Trial in Pancreatic Cancer
Study: IV ascorbate gemcitabine radiotherapy. Type: Phase I (safety dose escalation).
Protocol
· IV infusions of vitamin C during each radiotherapy session
· combination with standard chemotherapy.
Objective: To verify whether ascorbate increases tumor radiosensitivity.
4. Multicenter trial in advanced pancreatic cancer (follow-up to the Iowa program)
This study builds on a 20-year research program on vitamin C.
· high-dose vitamin C EV
· combined with modern chemotherapy
Preliminary results
· significant increase in survival
· good tolerability.
Next step: larger Phase III trial.
5. Trial of Metabolic Cancer Therapy with Vitamin C
An emerging line of research considers vitamin C as a metabolic anticancer therapy.
Recent reviews report several ongoing clinical studies on:
- tumore del pancreas
- colon cancer
- tumors with KRAS/BRAF mutations
- glioblastoma.
Biological hypothesis:
· Ascorbate at high concentrations generates hydrogen peroxide that is selective for tumor cells.
Summary of the most promising trials
Tumor Trial Type Status Metastatic pancreas vitamin C gemcitabine nab-paclitaxel promising phase II results Glioblastoma vitamin C radio temozolomide phase II Locally advanced pancreas vitamin C chemo-radiotherapy phase I Advanced pancreas follow-up randomized trial expansion phase III planned KRAS/BRAF tumors metabolic trials ongoing studies
Scientific conclusion (2025): The most convincing results so far concern:
- tumore del pancreas
- glioblastoma
But all the studies are still Phase I–II. Larger Phase III trials are needed to definitively demonstrate a clinical benefit. Why are some oncologists (like those at the University of Iowa) so confident in vitamin C, while most of the oncology community remains skeptical? The scientific history behind this controversy is quite surprising.
Oral vs. Intravenous Vitamin C This is a key point.
- Oral: the body limits absorption → relatively low plasma levels
- Intravenous: blood concentrations up to 100 times higher. For this reason, many antitumor effects observed in studies occur only with IV infusion.
4. Position of the guidelines and scientific reviews
Systematic reviews and cancer societies generally conclude:
· There is no solid evidence that vitamin C alone cures cancer.
· may have potential as an adjuvant therapy (in combination with chemotherapy or radiotherapy)
· Larger and more controlled clinical trials are needed
Furthermore, taking antioxidant supplements has not been shown to prevent cancer in the general population.
5. Possible risks of high doses
High doses (especially IV) can cause:
· kidney stones
· hemolysis in patients with G6PD deficiency
· interactions with some oncological therapies
For this reason it is only used in clinical protocols or under medical supervision.
Conclusion (current scientific consensus):
· there is promising biological evidence and preliminary clinical studies
· high-dose vitamin C is not a proven cancer therapy
· it could become a complementary treatment in some tumors, but larger trials are needed.
1. Studio meccanicistico molto citato Science (2015) “Vitamin C selectively kills KRAS and BRAF mutant colorectal cancer cells”
Main result
· high concentrations of vitamin C selectively kill tumor cells with KRAS or BRAF mutations (common in colon cancer).
· the mechanism:
or tumor cells take up dehydroascorbate via GLUT1
or oxidative stress is generated
or the glycolytic enzyme GAPDH is inhibited, causing cellular energy crisis.
Importance
· provided a strong biological basis for clinical trials.
Limit
· mainly preclinical study (cells animal models).
2. Cancer Research Radiosensitization Study (2015) – Highly cited line of research in oncology “Pharmacological ascorbate radiosensitizes pancreatic cancer”
Results
- High-dose ascorbate generates hydrogen peroxide (H₂O₂) which increases oxidative damage in tumor cells.
- combined with radiotherapy:
- reduces the survival of tumor cells
- slows tumor growth in mouse models.
Meaning
- suggests that vitamin C may enhance radio- and chemotherapy.
3. Trial clinico fase I (monoterapia EV) Cancer Chemotherapy and Pharmacology (2013)
Drawing
- patients with advanced solid tumors
- intravenous infusions up to 70–110 g/m².
Results
- plasma levels up to 49 mM
- well-tolerated therapy
- no objective tumor response in patients.
Interpretation
- demonstrates safety and pharmacokinetics, but not efficacy alone.
4. Phase I–II clinical trial (vitamin C chemotherapy) Integrative oncology clinical trials
Drawing
- IV vitamin C chemotherapy in patients with advanced tumors.
Results
- safe and well-tolerated treatment
- Some patients showed temporary stabilization of the disease and functional improvement.
Limit
- very small sample (≈14 patients).
5. Recent clinical trial on pancreas (much discussed) Redox Biology / randomized trial (2024)
Drawing
- vitamina C EV gemcitabina nab-paclitaxel
- metastatic pancreatic cancer.
Results
- median survival:
- 0 to 16 months with vitamin C
- 0 to 8.3 months with chemotherapy alone
- no significant increase in toxicity.
Limits
· very small number of patients (~34)
· Phase II study → confirmation needed with Phase III.
6. Systematic review of clinical trials Antioxidants (2018) Analysis of clinical trials on IV vitamin C:
Main conclusions:
- therapy is generally safe
- evidence of improved quality of life
- antitumor results still inconsistent or preliminary.
Summary of current scientific evidence
Strong evidence
· plausible antitumor molecular mechanisms
· safety of IV ascorbate
· possible synergy with chemotherapy or radiotherapy
Weak evidence
- few large randomized trials
- many studies with:
- few patients
- phase I–II
- exploratory endpoints
Current consensus in oncology
- it is not standard therapy
- it can be studied as an adjuvant therapy.
Conclusion:
Studies published in high-level journals suggest that pharmacological ascorbate has interesting biological mechanisms and promising preliminary clinical results, but robust phase III trials are still lacking to demonstrate a true clinical benefit.
Five of the most promising clinical trials (2023-2025) studying high-dose intravenous vitamin C (pharmacological ascorbate) as an adjunctive cancer therapy. They are the most cited in recent publications and clinical registries.
1. Randomized trial in metastatic pancreatic cancer (2024)
Study: IV vitamin C standard chemotherapy Drugs: gemcitabine nab-paclitaxel Phase: II randomized
Main results
- median survival:
- 8.3 months on chemotherapy alone
- disease progression:
- 6.2 months vs 3.9 months
no significant increase in toxicity. Published in Redox Biology (2024). It is considered one of the most promising clinical results to date.
2. Phase II trial in glioblastoma Study: IV vitamin C standard therapy (surgery radiation therapy temozolomide) Registry: NCT02344355 Parent center: University of Iowa
Protocol
· IV infusion 3 times a week during radio-chemo
- then 2 times a week during adjuvant chemotherapy.
Objective:
- Improve survival and response to radiotherapy in glioblastoma. This trial builds on a previous Phase I study that demonstrated the safety of combining temozolomide and radiotherapy.
3. Vitamin C chemo-radiotherapy trial in pancreatic cancer: Study: IV ascorbate gemcitabine radiotherapy: Type: phase I (safety dose escalation)
Protocol
· IV infusions of vitamin C during each radiotherapy session
· combination with standard chemotherapy.
Objective:
· to verify whether ascorbate increases the radiosensitivity of the tumor.
4. Multicenter trial in advanced pancreatic cancer (follow-up to the Iowa program)
This study builds on a 20-year research program on vitamin C.
Design
· high-dose vitamin C EV
· combined with modern chemotherapy
Preliminary results
· significant increase in survival
· good tolerability.
Next step: larger Phase III trial.
5. Trials on Metabolic Cancer Therapy with Vitamin C An emerging line of research considers vitamin C as a metabolic anticancer therapy. Recent reviews report several ongoing clinical trials on:
· tumore del pancreas
· colon cancer
· tumors with KRAS/BRAF mutations
· glioblastoma.
Biological hypothesis:
· Ascorbate at high concentrations generates hydrogen peroxide that is selective for tumor cells.
Summary of the most promising trials: Tumor > Type of trial
- Metastatic pancreas
vitamin C gemcitabine nab-paclitaxel
promising phase II results
Glioblastoma
vitamin C radio temozolomide
phase II
Locally advanced pancreas
vitamin C chemo-radiotherapy
fase I
Advanced pancreas
randomized follow-up trial
Phase III expansion planned
Tumori KRAS/BRAF
metabolic trials
studies in progress
Scientific conclusion (2025): The most convincing results so far concern:
- tumore del pancreas
- glioblastoma
But all the studies are still Phase I–II. Larger Phase III trials are needed to definitively demonstrate a clinical benefit.