Vitamins. Antioxidants
Brand names – supplements: Emergen-C, NOW Foods Vitamin C-1000, Thorne Buffered C Powder, Ester-CSupplements are not tested in clinical trials and are not registered as medications.
Updated · Methodology
First line
First-line treatment for scurvy. Treatment dose is 200 mg daily for 5 days or 1,000 mg daily for 1–2 weeks, then maintenance at the physiological 75–90 mg daily. Symptoms (bleeding gums, petechiae, arthralgia) resolve over 2–4 weeks. BMJ 2018 and BNF support oral treatment; parenteral administration is reserved for severe malabsorption.
Sources
ICD-10: E54 · ICD-11: 5B56.0
Individual decision
The evidence base is weak and mixed. Supplemental vitamin C 500–1,000 mg daily is considered in patients with nutritional deficiency, after major surgery, with burns, or in older adults with pressure ulcers – only as part of overall nutritional correction. NPUAP/EPUAP 2019 recommend vitamin C as part of nutritional support in pressure ulcers. The 2014 Cochrane review on vitamins and pressure ulcer healing (Langer 2014) is methodologically weak; large RCTs are absent. In patients without confirmed deficiency, isolated vitamin C does not affect wound healing time. The foundational approach is nutritional status assessment and correction of deficiencies as a whole, not mega-dose ascorbic acid.
Sources
ICD-10: T14.1 · ICD-11: ND56.1
The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.
Not recommended
Ascorbic acid (vitamin C) is a nutrient often promoted in supplements as a way to slow aging and extend lifespan. Convincing benefit for this use hasn't been shown: the evidence doesn't support that taking supplements delays aging or makes people live longer. What actually helps here is sleep, regular physical activity, a varied diet and not smoking, and most vitamin C comes from vegetables and fruit anyway.
Not recommended
Ascorbic acid (vitamin C) is widely offered and marketed as a remedy for tiredness – in supplements, effervescent tablets and vitamin blends. For chronic fatigue this use has no convincing benefit: there is no quality evidence that taking vitamin C relieves fatigue in people who are not deficient in it. Persistent fatigue responds to a different approach – finding the cause (poor sleep, anemia, thyroid problems, depression and other conditions) and treating that cause with a doctor. Do not take this product instead of a treatment with proven benefit, or you may miss a condition that needs real care.
ICD-10: R53 · ICD-11: MG22
Not recommended
The 2013 Cochrane review (29 RCTs, more than 11,000 participants) showed that regular vitamin C 200 mg daily or higher in the general population does not reduce respiratory infection incidence. In athletes under extreme physical stress, the risk drops by 50% with daily intake. In most adults, routine vitamin C for cold prevention has no proven benefit. Symptom duration reduction when started after onset is about 8% in adults – minimal clinical significance.
ICD-10: J00 · ICD-11: CA00
Not recommended
The 2014 Cochrane review did not confirm an effect of vitamin C on asthma symptoms or prevention of exercise-induced bronchospasm. International pulmonology societies () do not include vitamin C in asthma management standards. Small positive RCTs have not been reproduced.
ICD-10: J45.9 · ICD-11: CA23.21
Not recommended
Ascorbic acid (vitamin C) is an antioxidant often recommended for vascular health and to prevent heart attacks and strokes in people without heart disease. The benefit for this use has not been shown: vitamin C supplements do not lower the risk of heart attack, stroke, or death in people without established cardiovascular disease. What actually protects the heart and vessels are other steps – quitting smoking, managing blood pressure, cholesterol, and blood sugar, staying active, and eating well; extra vitamin C on top of a balanced diet adds nothing here.
Not recommended
High-dose vitamin C is not supported by international guidelines as cancer prevention or treatment. The mega-dose concept originates in Linus Pauling's 1970s publications and has not been confirmed in large subsequent RCTs. PDQ summary states clearly: RCTs have not confirmed an effect of high-dose ascorbic acid on cancer outcomes. Intravenous vitamin C drips at doses of 25–75 g offered in private clinics as «cancer treatment» or «prevention» fall outside NCCN, ESMO, and ASCO recommendations. Large meta-analyses (Zhang 2013, Luo 2014) showed no effect on all-cause or cardiovascular mortality. In patients with established cancer, high-dose vitamin C should be discussed with the treating oncologist because it may reduce the efficacy of some cytotoxic agents and radiotherapy.
Ascorbic acid (vitamin C) is a water-soluble cofactor for hydroxylases involved in collagen, carnitine, and neurotransmitter (noradrenaline, serotonin) synthesis. An antioxidant: it regenerates tocopherol and neutralises reactive oxygen species. Reduces Fe³⁺ to Fe²⁺ in the intestine, enhancing non-haem iron absorption. Not synthesised in humans and obtained only from diet. Body stores are small – 1,500–3,000 mg.
AEMPS summary of product characteristics (section 4.6): there are no controlled studies of ascorbic acid in pregnant women. If a pregnant woman takes high doses of the vitamin, the newborn may develop scurvy. As a precaution, ascorbic acid solution for injection is not used during pregnancy unless a doctor considers it essential, and the recommended dose must not be exceeded, as chronic overdose can harm the fetus and newborn.
Transfers into breast milk at physiological amounts. Supplementation at the RDA is safe. High-dose use during lactation is not justified.
Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.
Ascorbic acid 100–200 mg increases ferrous iron absorption by 10–15%. The effect is stronger when taken concurrently with iron preparations rather than separated in time.
4 pairs found. Sorted from critical to minor.
Mechanism
Ascorbic acid does not affect cetirizine metabolism. The two are often combined in symptomatic preparations for acute respiratory infections.
Symptoms
The combination usually causes no specific symptoms. Each drug's individual side effects remain.
Management
No dose adjustment needed. The combination is standard in symptomatic formulations for acute respiratory infections and allergy.
Mechanism
This pair does not subtract, it adds. Ascorbic acid reduces ferric iron to ferrous, the form the enterocyte absorbs, and counteracts the phytates and polyphenols that bind it. It is the only combination on this list that is sought deliberately.
Symptoms
No adverse effects of its own. At very high vitamin C doses alongside iron some people notice more stomach upset, which settles on a lower dose.
Management
Use it: iron with a glass of orange juice, or with vitamin C built into the tablet, performs better than iron alone. What does help is keeping it away from tea, coffee and dairy, which pull the other way. In haemochromatosis or iron overload this boost stops being desirable.
Pair details →Iron oral (salts: sulfate, bisglycinate, fumarate, gluconate, polymaltose; heme iron polypeptide, lactoferrin) →
Mechanism
Ascorbic acid raises gastric acidity and improves levothyroxine absorption in patients with atrophic gastritis or hypochlorhydria. In healthy patients the effect is minimal.
Symptoms
The combination usually causes no specific symptoms. Each drug's individual side effects remain.
Management
In patients with confirmed atrophic gastritis or PPI intolerance, ascorbic acid 500 mg with levothyroxine improves absorption. In healthy patients, no specific adjustment is needed. Monitor TSH on the usual schedule.
Mechanism
No direct pharmacokinetic interaction. Vitamin C increases iron absorption, not metformin's.
Symptoms
The combination usually causes no specific symptoms. Each drug's individual side effects remain.
Management
No dose adjustment needed. In diabetics on metformin, ascorbic acid may improve plant-source iron absorption in patients with deficiency.
Sources
Verbatim lines from the interaction sections, in the language of the label
«Cianocobalamina (vitamina B12): el ácido ascórbico en grandes dosis podría reducir las cantidades de cianocobalamina disponibles en suero y reservas (dosis elevadas de ácido ascórbico pueden destruir…»AEMPS, section 4.5 · Open on CIMA
«DRUG INTERACTIONS: • Warfarin: Continue standard monitoring ( 7.3 ).»FDA, section 7 · Open on DailyMed
«Antibiotics: Ascorbic acid may decrease activities of erythromycin, kanamycin, streptomycin, doxycycline, and lincomycin. Bleomycin is inactivated in vitro by ascorbic acid. If the antibiotic…»FDA, section 7 · Open on DailyMed
«Antibiotics: Ascorbic acid may decrease activities of erythromycin, kanamycin, streptomycin, doxycycline, and lincomycin. Bleomycin is inactivated in vitro by ascorbic acid. If the antibiotic…»FDA, section 7 · Open on DailyMed
«Ciclosporina: datos limitados sugieren que los suplementos antioxidantes como el ácido ascórbico puede reducir los niveles sanguíneos de ciclosporina.»AEMPS, section 4.5 · Open on CIMA
«Disulfiram: Dosis crónicas o altas de Ácido ascórbico pueden interferir con la eficacia del disulfiram.»AEMPS, section 4.5 · Open on CIMA
«Anticoagulantes orales como warfarina y acenocumarol: podría verse modificada su acción por el ácido ascórbico en grandes dosis.»AEMPS, section 4.5 · Open on CIMA
«Suplementos de ácido ascórbico: pueden disminuir la absorción de vitamina B12. Para disminuir este efecto se sugiere que el ácido ascórbico se tome 2 o más horas después de los alimentos o de…»AEMPS, section 4.5 · Open on CIMA
«La absorción del hierro puede incrementarse por la administración simultánea de 200 mg de ácido ascórbico y reducirse con la administración simultánea de antiácidos, colestiramina o inhibidores de la…»AEMPS, section 4.5 · Open on CIMA
«Ascórbico, ácido: altas dosis de ácido ascórbico (2 g/AEMPS, section 4.5 · Open on CIMA
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Ascorbic acid is evaluated for the following indications with varying evidence strength: Scurvy (vitamin C deficiency) (evidence tier A), Anti-aging and longevity (evidence tier D), Wound healing support (evidence tier D). See the full indication matrix with dosing and citations above on this page.
Common side effects of Ascorbic acid (≥ 1 in 100): Diarrhoea, abdominal cramps at doses above 1,000 mg daily, Nausea, Heartburn. See the Safety section for uncommon and serious reactions.
AEMPS summary of product characteristics (section 4.6): there are no controlled studies of ascorbic acid in pregnant women. If a pregnant woman takes high doses of the vitamin, the newborn may develop scurvy. As a precaution, ascorbic acid solution for injection is not used during pregnancy unless a doctor considers it essential, and the recommended dose must not be exceeded, as chronic overdose can harm the fetus and newborn.
Transfers into breast milk at physiological amounts. Supplementation at the RDA is safe. High-dose use during lactation is not justified.
Ascorbic acid is contraindicated in: G6PD deficiency – haemolysis risk at high doses; Thrombophlebitis, thrombosis tendency (for high doses); Haemochromatosis, thalassaemia, sideroblastic anaemia; Oxalosis, calcium oxalate kidney stones; Hypersensitivity to vitamin C. Full list in the Safety section.
the mega-dose idea originates with Linus Pauling's 1970s publications. Subsequent large RCTs did not reproduce the effect. NCI PDQ summary states: high-dose vitamin C does not affect cancer outcomes. NCCN, ESMO, and ASCO do not include vitamin C in cancer prevention recommendations.
intravenous infusions of 25–75 g of vitamin C offered in private clinics as «cancer treatment» fall outside international guidelines. Large RCTs have not shown clinically meaningful effects on tumour progression or survival. In chemotherapy patients, high-dose vitamin C may reduce the efficacy of some drugs (bortezomib, cisplatin).
the subjective energising sensation from IV vitamins has not been reproduced in RCTs. «Vitamin drips» are a paid marketing service, not treatment. Chronic fatigue requires differential workup: anaemia, hypothyroidism, depression, iron or B12 deficiency.
systematic reviews show no effect on cold incidence in the general population. Symptom duration reduction during treatment is about 8 % – clinically insignificant.
large RCTs Physicians' Health Study II 2012, HOPE 2000, HOPE-TOO 2005 showed no effect of antioxidant vitamins on myocardial infarction or stroke. ESC and AHA do not include vitamin C in CVD prevention.
doses above 2,000 mg daily increase the risk of oxalate kidney stones, diarrhoea, and impaired B12 absorption. In G6PD deficiency, high doses cause haemolysis. IV mega-doses in patients with renal impairment have caused acute oxalate nephropathy.
the ascorbic acid molecule is identical regardless of origin. Bioavailability is comparable. Natural sources are preferred for accompanying phytonutrients and fibre – not for vitamin C itself.
Direct links to regulator labels. Open in a new tab.
Ashwagandha (Withania somnifera), Astaxanthin, Bacopa monnieri (brahmi), Beta-carotene, Cranberry (Vaccinium macrocarpon), Maca, Propolis (bee product), Spermidine