Oral Vitamin C and intravenous Vitamin C have vastly different pharmacokinetics and effects on cancer.
- Low dose vitamin C (oral) is anti-oxidant and may attenuate chemotherapy:
Chemosensitizing effect of vitamin C in combination with 5-fluorouracil in vitro
https://www.ncbi.nlm.nih.gov/pubmed/12929582
"only a high concentration of vitamin C increased the cytotoxicity of 5-FU"
We did a data extraction project for 81 trials using oral or intravenous IV as a cancer therapy! You can see the whole project at https://sysrev.com/p/6737. Basically we imported 81 VitC trials from clinicaltrials.gov and extracted dose levels, administration methods, placebo usage, and some other data.
High-dose vitamin C enhances cancer immunotherapy https://stm.sciencemag.org/content/12/532/eaay8707/
Takeaways:
Oral Vitamin C and intravenous Vitamin C have vastly different pharmacokinetics and effects on cancer.
- Low dose vitamin C (oral) is anti-oxidant and may attenuate chemotherapy:
Chemosensitizing effect of vitamin C in combination with 5-fluorouracil in vitro https://www.ncbi.nlm.nih.gov/pubmed/12929582 "only a high concentration of vitamin C increased the cytotoxicity of 5-FU"
Ascorbic acid attenuates antineoplastic drug 5-fluorouracil induced gastrointestinal toxicity in rats by modulating the expression of inflammatory mediators https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5598240/
- High dose vitamin C (intravenous) is pro-oxidant
- High dose vitamin C (intravenous) alone slows tumor growth
- High dose vitamin C (intravenous) combined with immunotherapy has a synergistic effect
High dose vitamin C (intravenous) also synergizes with chemotherapy and spares healthy cells https://stm.sciencemag.org/content/6/222/222ra18
If you are in chemotherapy or immunotherapy, stay away from low doses of oral anti-oxidant supplements such as Vitamin C.