With oral nonheme iron
Complementary evidenceLv3
Vitamin C can increase the absorption and bioavailability of nonheme iron.
Interaction evidence source All research profiles
Vitamin / antioxidant
Ascorbic acid
Prepared by the ezGLP team. Sources last checked . Profile reviewed .
Also known as Vitamin C
Routes represented in the knowledgebase: Oral / Other / unspecified.
Educational overview
Oral supplement; FDA-approved IV use is limited to short-term scurvy treatment when oral therapy is not possible or sufficient.
Ascorbic acid (vitamin C) is a water-soluble vitamin that humans cannot synthesize because the gene for L-gulonolactone oxidase is nonfunctional. It acts as an electron donor for enzymes that hydroxylate collagen, synthesize carnitine and norepinephrine, and amidate peptide hormones, and it regenerates vitamin E and scavenges reactive oxygen species. Its absence causes scurvy, marked by bleeding gums, poor wound healing, and fatigue. The Food and Nutrition Board publishes an RDA and a tolerable upper intake level, and intestinal absorption falls steeply as intake rises, so plasma concentrations are tightly regulated with oral intake. Chemically, ascorbic acid is classified as a vitamin and antioxidant, distinct from the drug class of any product containing it.
Evidence for treating deficiency is definitive, and NIH pharmacokinetic work by Padayatty and Levine established that intravenous administration bypasses intestinal control and produces plasma concentrations far higher than any oral intake. Beyond deficiency, results are mixed. A 2013 Cochrane review found that regular supplementation does not reduce the incidence of colds in the general population but modestly shortens their duration. In cancer, small trials and phase I and II studies of high-dose intravenous vitamin C have produced inconsistent results with no confirmed survival benefit. In sepsis, the 2021 VICTAS trial found no benefit, and the 2022 LOVIT trial reported a higher risk of death or persistent organ dysfunction with intravenous vitamin C.
Oral ascorbic acid is sold as a dietary supplement in the United States and as a food supplement in the European Union, with no prescription required. Ascor, an ascorbic acid injection, was approved by FDA in 2017 for short-term treatment of scurvy in people who cannot take or absorb oral vitamin C; the label notes that it is not indicated for other uses. Before that approval, injectable ascorbic acid had been marketed for decades as an unapproved drug, and FDA has since acted against unapproved injectable vitamin products distributed to clinics. High-dose intravenous vitamin C offered at wellness clinics for cancer, fatigue, or immunity is a compounded preparation or off-label use that no regulator has approved.
Ascorbic acid degrades through oxidation, so injectable products are stored under refrigeration, protected from light, and used promptly once a vial is entered; the Ascor label specifies single-dose vials without preservative. Oral tablets, powders, and effervescent forms are stored at room temperature away from moisture and heat. For a dose log or inventory record, relevant details include the route, the concentration and total amount for any infusion, lot number, and the prescribing or compounding source. Two effects are documented for high intravenous doses: falsely elevated readings on some point-of-care glucose meters, and oxalate deposition in the kidneys, which has caused acute kidney injury in case reports, particularly in people with impaired renal function.
- Category
- Vitamin / antioxidant
- Routes represented
- Oral / Other / unspecified
- Storage context
- Follow the product or pharmacy label; requirements vary by route and formulation.
Published literature
No verified PubMed or DOI link is available for this entry.
Safety evidence
Common or reported: diarrhea, nausea, abdominal cramps.
Serious or important: kidney-stone or oxalate risk in susceptible people, IV oxalate nephropathy and laboratory interference.
IV risks should not be generalized to ordinary oral use.
Safety evidence sourceInteraction evidence
These are general, pairwise evidence notes. Green identifies the potential-synergy category, while Lv3/Lv2/Lv1 communicates evidence strength; it does not guarantee benefit or cancel a safety warning.
Common questions
Does high-dose IV vitamin C cure cancer?
No controlled trial has shown that it does. Intravenous vitamin C reaches plasma concentrations that kill cancer cells in laboratory studies, but human trials have been small and inconsistent. Early oral-dose trials at the Mayo Clinic found no benefit, and later phase I and II studies of intravenous administration report good tolerability and, in some cases, improved quality of life, but no confirmed effect on survival. The NIH Office of Dietary Supplements describes the evidence as mixed and calls for larger trials.
Is injectable vitamin C FDA approved?
One product is. Ascor (ascorbic acid injection) was approved in 2017 for short-term treatment of scurvy in patients for whom oral administration is not possible, insufficient, or contraindicated. Its label states that it is not indicated for other conditions. Other injectable ascorbic acid products sold to clinics have been marketed without approval, and high-dose infusions for cancer, immune support, or fatigue are compounded or off-label uses that FDA has not evaluated for safety or effectiveness.
Does vitamin C prevent colds?
In the general population, regular vitamin C supplementation has not been shown to reduce how often people catch colds, according to a Cochrane review of placebo-controlled trials. It did modestly shorten the duration and severity of colds when taken continuously, and reduced incidence in a subgroup of people under heavy short-term physical stress, such as marathon runners and soldiers in subarctic conditions. Starting vitamin C after symptoms begin showed no consistent benefit.
Can too much vitamin C harm the kidneys?
Ordinary oral intake is excreted in urine and the tolerable upper intake level is set mainly on gastrointestinal effects such as diarrhea. Vitamin C is metabolized to oxalate, and very high intakes, especially by the intravenous route, have caused oxalate crystal deposition and acute kidney injury in published case reports, most often in people with pre-existing kidney impairment or a history of kidney stones. People with G6PD deficiency have developed hemolysis after high-dose infusions.
Further reading
- NIH Office of Dietary Supplements, Vitamin C fact sheet for health professionals
- DailyMed, Ascor (ascorbic acid) injection
- FDA approval label, Ascor (2017)
- Padayatty et al., vitamin C pharmacokinetics for oral and intravenous use, Ann Intern Med 2004
- Hemila and Chalker, vitamin C for the common cold, Cochrane 2013
- Lamontagne et al., LOVIT trial of intravenous vitamin C in sepsis, N Engl J Med 2022
- Sevransky et al., VICTAS trial, JAMA 2021
- FDA warning on unapproved injectable vitamin products distributed to clinics
Summarised from published literature for reference only, with citations to the source. Evidence is graded as reported and is not a recommendation to combine, dose, or use any compound.
For personal tracking and education only. Not medical advice, diagnosis, or treatment, and not a medical device. Peptides may be prescription-only or unapproved where you live. Consult a licensed healthcare professional.