Vitamin C

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Specifically for Flu

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Why it works for Flu:

Vitamin C is a potent water-soluble antioxidant that gives the immune system a boost through its increase in T-lymphocyte activity, phagocyte function, leukocyte mobility, and possible antibody and interferon production. Its effects on the immune system may also be potentially explained through protection against oxidative stress generated during infections. Vitamin C in the Prevention and Treatment of the Common Cold - PMC

However, the effectiveness is limited and context-dependent. Regular ingestion of vitamin C had no effect on common cold incidence in the ordinary population, based on 29 trial comparisons involving 11,306 participants Vitamin C for preventing and treating the common cold | Cochrane, though regular supplementation had a modest but consistent effect in reducing the duration of common cold symptoms Vitamin C for preventing and treating the common cold | Cochrane.

In adults the duration of colds was reduced by 8% (3% to 12%) and in children by 14% (7% to 21%) Vitamin C for preventing and treating the common cold | Cochrane

Vitamin C significantly decreased the severity of the common cold by 15% (95% CI 9–21%) Vitamin C reduces the severity of common colds: a meta-analysis | BMC Public Health | Full Text

The finding that vitamin C may have a greater effect on more severe measures of the common cold is therefore important Vitamin C reduces the severity of common colds: a meta-analysis | BMC Public Health | Full Text

How to use for Flu:

Preventive dosing:

Regular vitamin C supplementation (at an average dose of 1-2 g/day) resulted in a significant reduction in the duration of common colds Vitamin C in the Prevention and Treatment of the Common Cold - PMC
In eleven of the comparisons 1 g/day vitamin C was administered, 2 g/day was administered in two comparisons Vitamin C reduces the severity of common colds: a meta-analysis | BMC Public Health | Full Text

Therapeutic dosing (when symptoms appear):

Those in the test population reporting symptoms were treated with hourly doses of 1000 mg of Vitamin C for the first 6 hours and then 3 times daily thereafter The effectiveness of vitamin C in preventing and relieving the symptoms of virus-induced respiratory infections - PubMed
Intravenous Vitamin C (IVC) therapy which consisted of 1,000 cc of lactated Ringer's solution containing 50 grams of sodium ascorbate, a pH-neutral form of vitamin C. This was infused over about one and a half hour. This same regimen was repeated for a total of 3 infusions over 3 days High Dose Vitamin C and Influenza: A Case Report - ISOM (for severe cases)

Important limitations:

The results indicated that therapeutic vitamin C supplementation had no consistent effect on cold duration or severity Vitamin C in the Prevention and Treatment of the Common Cold - PMC
When vitamin C was tested for treatment of colds in 7 separate studies, it was found to be no more effective than placebo at shortening the duration of cold symptoms Vitamin C for Colds: Benefits, Side Effects, Uses

Scientific Evidence for Flu:

Major systematic reviews and meta-analyses:

Cochrane Review (2013): Twenty-nine trial comparisons involving 11,306 participants contributed to the meta-analysis on the risk ratio (RR) of developing a cold whilst taking vitamin C regularly over the study period Vitamin C for preventing and treating the common cold | Cochrane
BMC Public Health Meta-analysis (2023): Fifteen comparisons from 10 trials which reported both mild and severe symptoms were identified. All trials were randomized and double-blind. Compared to placebo, vitamin C significantly decreased the severity of the common cold by 15% Vitamin C reduces the severity of common colds: a meta-analysis | BMC Public Health | Full Text
Limited therapeutic evidence: The review included 7 studies that analyzed the therapeutic effect of vitamin C. Unlike the aforementioned studies where vitamin C was administered regularly and prophylactic to cold onset, the therapeutic effect of vitamin C was examined by analysis of studies in which vitamin C was given in response to onset of cold symptoms Vitamin C in the Prevention and Treatment of the Common Cold - PMC

Key study findings:

9 randomized placebo-controlled trials were included in our meta-analysis Extra Dose of Vitamin C Based on a Daily Supplementation Shortens the Common Cold: A Meta-Analysis of 9 Randomized Controlled Trials - PMC showing modest benefits
Vitamin C in megadoses administered before or after the appearance of cold and flu symptoms relieved and prevented the symptoms in the test population compared with the control group The effectiveness of vitamin C in preventing and relieving the symptoms of virus-induced respiratory infections - PubMed

Negative evidence:

Doses of vitamin C in excess of 1 g daily taken shortly after onset of a cold did not reduce the duration or severity of cold symptoms in healthy adult volunteers when compared with a vitamin C dose less than the minimum recommended daily intake Mega-dose vitamin C in treatment of the common cold: a randomised controlled trial - PubMed

Specific Warnings for Flu:

Dosage warnings:

The RDA, or recommended daily allowance, is 90 milligrams for men and 75 milligrams for women. High doses of vitamin C (greater than 2,000 milligrams per day for adults) may cause kidney stones, nausea, and diarrhea Vitamin C for Colds: Benefits, Side Effects, Uses
The most common side effects of vitamin C supplements are listed below. These side effects are more likely to occur in people taking more than 1,000 mg daily Vitamin C Supplements: Uses, Side Effects, Interactions, Pictures, Warnings & Dosing - WebMD

Common side effects from high doses:

Vitamin C is usually well tolerated, although high doses can cause diarrhea, nausea, and stomach cramps Vitamin C Supplements: Uses, Side Effects, Interactions, Pictures, Warnings & Dosing - WebMD
Nonserious adverse events were experienced by 39.5% of patients in the ascorbic acid arm... The most common nonserious adverse effects in this study were gastrointestinal events Vitamin C | COVID-19 Treatment Guidelines

Serious warnings:

Vitamin C supplements may cause allergic reactions, which can be serious Vitamin C Supplements: Uses, Side Effects, Interactions, Pictures, Warnings & Dosing - WebMD
You should not use ascorbic acid if you are allergic to it Vitamin C Uses, Side Effects & Warnings

High-dose IV vitamin C concerns: Recent evidence shows Analysis showed that these vitamin infusions did not improve outcomes for patients. Once researchers had evidence that the treatment was ineffective, this part of the trial was stopped. After a full analysis of the data, results indicated that it may even be harmful High dose vitamin C ineffective in treatment of Covid-19 while cholesterol-lowering medicine improves outcomes | Imperial College Healthcare NHS Trust for hospitalized COVID-19 patients.

Drug interactions and medical conditions:

Ask a doctor or pharmacist if Vitamin C is safe to use if you have or have ever had Vitamin C Uses, Side Effects & Warnings certain medical conditions
High concentrations of circulating vitamin C may affect the accuracy of point-of-care glucometers Vitamin C | COVID-19 Treatment Guidelines

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General Information (All Ailments)

Note: You are viewing ailment-specific information above. This section shows the general remedy information for all conditions.

What It Is

Vitamin C is a water-soluble essential vitamin that humans must obtain from the diet because the body cannot synthesize it. It is found most abundantly in fruits (especially citrus, kiwi, berries) and vegetables (peppers, broccoli, tomatoes). In supplement form it appears as pure ascorbic acid, buffered salts (ascorbates), liposomal C, or injectable forms in clinical settings.

How It Works

Vitamin C acts primarily as a reducing agent (antioxidant). It donates electrons to neutralize reactive oxygen species and regenerate other antioxidants such as vitamin E and glutathione. In cells, this redox activity protects lipids, proteins, and DNA from oxidative damage.

It is also a required cofactor for several enzymatic reactions:

Collagen synthesis — hydroxylation of proline and lysine residues; essential for stable connective tissue, wound closure, vascular integrity, skin elasticity.
Catecholamine synthesis — converts dopamine to norepinephrine in neurons and adrenal tissue.
Carnitine synthesis — impacts mitochondrial fatty acid transport and cellular energy.
Immune interfacing — influences neutrophil motility and kill-capacity, supports epithelial barrier integrity, and can modulate inflammatory mediators.

Because it is water-soluble with limited tissue storage, excess is rapidly cleared in urine.

Why It’s Important

Vitamin C supports physiological resilience at multiple levels:

Connective tissue and vascular health: Adequate C keeps vessels less fragile, supports skin and mucosa, and accelerates wound healing.
Infection response: During infection and inflammatory stress, leukocytes consume vitamin C at high rates; levels fall rapidly when sick, which is one reason intake demand rises.
Oxidative load buffering: High oxidative states — e.g. smoking, heavy physical training, chronic inflammation, diabetes, pollution exposure — increase turnover and raise needs.
Classical deficiency consequence: Insufficiency leads to scurvy (gingival bleeding, corkscrew hairs, poor wound healing, petechiae, anemia, fatigue) — illustrating the vitamin’s structural and hematologic roles.

Considerations

Intake & upper limits

Typical dietary intake from whole foods is safe. Oral intakes above ~200–400 mg/day show diminishing incremental absorption due to saturable transport; much of very high oral dosing is excreted. Intakes >1–2 g/day can trigger osmotic GI upset (bloating, loose stools).

Kidney stones

High-dose chronic vitamin C can increase urinary oxalate; in predisposed individuals this may elevate calcium oxalate stone risk.

Glucose readings & labs

Very high doses can artifactually interfere with some point-of-care glucose meters and certain lab assays.

Iron metabolism

Vitamin C enhances non-heme iron absorption; beneficial in iron deficiency but potentially problematic in conditions of iron overload (hemochromatosis).

Route differences

Intravenous vitamin C yields transient supraphysiologic plasma levels unattainable orally. These have been explored in certain critical-care or adjunct oncology contexts, but this is not equivalent to routine supplementation and should be considered a medical intervention.

Population demand shifts

Smokers, people under chronic inflammatory/metabolic stress, and individuals with low fruit/vegetable intake tend to have lower baseline levels and higher physiological “burn rate.”

Helps with these conditions

Vitamin C is most effective for general wellness support with emerging research . The effectiveness varies by condition based on clinical evidence and user experiences.

Common Cold 0% effective

Flu 0% effective

COVID-19 0% effective

Asthma 0% effective

Acne 0% effective

UTI 0% effective

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Detailed Information by Condition

Common Cold

0% effective

Vitamin C is a water-soluble vitamin that is naturally present in some foods, added to others, and available as a dietary supplement. Vitamin C is req...

0 votes Updated 4 weeks ago 3 studies cited

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