vitaminNot FDA-approvedOTC supplementAvailable over the counter in the US as a dietary supplementThe Cochrane review found regular supplementation did not reduce cold incidence in the general population but modestly shortened cold duration
Vitamin CBenefits, Dosage & Interactions
Also known as: ascorbic acid
Vitamin C, also known as ascorbic acid, is an essential water-soluble vitamin that plays a crucial role in numerous physiological functions. As an antioxidant, it helps protect cells from damage caused by free radicals. Research on Vitamin C focuses on immune function, heart and circulatory health, and tissue recovery.
How much Vitamin C do people take?
The Cochrane review pooled trials using regular vitamin C supplementation of 200 mg/day or more, most commonly 1–2 g/day. Route reported: Oral. Frequency reported: Once daily to divided doses across the pooled trials. These are amounts documented in the cited studies and labels for Vitamin C — they are reported for reference, not a recommendation. Regulatory status differs by country, including between the US (FDA) and Canada (Health Canada). Confirm any amount with a licensed clinician before you take it.
See the full reported protocol and its sourcesResearched by DoseRoutine Research TeamReviewed for accuracy by Nicholas Alexander, RSE, SO, PMPLast updated Educational reference only — not medical advice. Always confirm dosing and safety decisions with a licensed clinician.
Evidence: Moderate — Covered by a systematic review, without regulatory approval.
Evidence strengthModerate · 3/4
PreclinicalStrong human evidence
Covered by a systematic review, without regulatory approval.
Whole-body biological half-life
Not applicable
Typical timing
in the morning
Default unit
mg
What published protocols report
Ranges documented in the literature, shown for reference. DoseRoutine does not recommend an amount — your prescriber or the product label sets the dose.
- Reported amounts
- The Cochrane review pooled trials using regular vitamin C supplementation of 200 mg/day or more, most commonly 1–2 g/day[1]
- Route studied
- Oral[1]
- Frequency
- Once daily to divided doses across the pooled trials[1]
- Cycle length
- Ranged from single-season winter periods to multi-year supplementation across the pooled trials[1]
- Half-life
- Plasma ascorbate half-life is on the order of hours, though tissue stores are replenished with regular intake[1]
- Storage
- Room temperature, away from moisture and light[1]
Reported for Vitamin C in the cited sources. Published ranges are not dosing advice.
References & evidence
Documents the Vitamin C entry is written from. Each number matches an inline marker above.
- [1]Vitamin C for preventing and treating the common coldHemilä H, Chalker E · Cochrane Database of Systematic Reviews · 2013 · Peer-reviewed · PMID 23440782
References & Evidence
Sources on this page that document Vitamin C dosing, timing and safety.
- [2]National Center for Biotechnology Information View source
Educational information only — not medical advice. Dose ranges vary by person, indication and prescriber.
What is Vitamin C studied for?
Deficiency-driven — not a performance booster
Vitamins primarily help when you're actually low. Extra doses on top of normal levels rarely add strength, endurance, or fat loss, and some fat-soluble vitamins (A, D, E, K) can build up to harmful levels.
- Confirm a deficiency with bloodwork before supplementing long-term (e.g. 25(OH)D for vitamin D, B12/folate, ferritin, magnesium RBC).
- Talk to your doctor or a registered dietitian about the right dose for your labs, medications, and conditions — especially in pregnancy, kidney/liver disease, or while on blood thinners.
- Re-test every 3–6 months and stop or lower the dose once levels are in range.
Educational information only — not medical advice. See our AI & medical policy.
What is Vitamin C?Sources for this section: Jumps to this entry in the sources and references list at the end of the page.
Vitamin C, also known as ascorbic acid, is an essential water-soluble vitamin that plays a crucial role in numerous physiological functions. As an antioxidant, it helps protect cells from damage caused by free radicals. The human body cannot synthesize Vitamin C, meaning it must be obtained through diet or supplementation. Key dietary sources include citrus fruits, bell peppers, broccoli, and tomatoes. It is involved in collagen formation, which is vital for skin, blood vessels, bones, and cartilage. It also contributes to immune function, supports iron absorption, and is involved in neurotransmitter biosynthesis. Serious deficiency of Vitamin C leads to scurvy, a condition characterized by fatigue, gum disease, and poor wound healing. While scurvy is rare in developed countries, suboptimal intake can still affect health. (NIH Office of Dietary Supplements, MedlinePlus)
Why vitamins for endurance: Vitamin C supports iron absorption, immune resilience under heavy training, and collagen for connective tissue. Very high doses around training may blunt some training adaptations — modest daily intake that covers dietary gaps is the safer play.
References: NIH ODS Vitamin C fact sheet (2021); Paulsen G et al. Vitamin C and E supplementation hampers cellular adaptation to endurance training. J Physiol. 2014;592(8):1887-901; Braakhuis AJ. Effect of vitamin C supplements on physical performance. Curr Sports Med Rep. 2012;11(4):180-4.
What does the research say about Vitamin C?
Tap a section to expand.
Vitamin C functions primarily as a potent antioxidant, donating electrons to neutralize free radicals, which are unstable molecules that can cause cellular damage and contribute to aging and various diseases. This antioxidant activity is fundamental to its protective roles within the body. Beyond its antioxidant capacity, Vitamin C is a required cofactor for several enzymatic reactions. It is essential for the biosynthesis of collagen, the main structural protein in connective tissues, through the hydroxylation of proline and lysine residues. This process is critical for wound healing, maintenance of blood vessel integrity, and bone health. Vitamin C also participates in the biosynthesis of carnitine, a molecule important for fatty acid metabolism, and norepinephrine, a neurotransmitter. It enhances the absorption of non-heme iron (iron from plant sources) by reducing it to a more absorbable ferrous state in the gut. Furthermore, Vitamin C influences immune function by supporting various cellular functions of both the innate and adaptive immune systems. Its role in wound healing is partly attributed to its involvement in collagen synthesis and its anti-inflammatory properties. (Linus Pauling Institute, PubChem)
Source for this section: Sources for How does Vitamin C work?: Jumps to this entry in the sources and references list at the end of the page.
Vitamin C has been associated with several potential health benefits across various body systems:
* **Antioxidant Protection:** As a powerful antioxidant, Vitamin C helps protect the body's cells from oxidative stress and damage caused by free radicals, which are implicated in the development of chronic diseases and aging processes. (NIH Office of Dietary Supplements)
* **Immune System Support:** Vitamin C contributes to immune defense by supporting various cellular functions of both the innate and adaptive immune systems. It can enhance the production and function of white blood cells, such as phagocytes and lymphocytes, and may reduce the duration and severity of the common cold in some individuals. (Cochrane Review, Linus Pauling Institute)
* **Collagen Formation:** Essential for the synthesis of collagen, Vitamin C is crucial for the health and integrity of skin, blood vessels, bones, cartilage, and teeth. Adequate intake supports wound healing and contributes to maintaining healthy connective tissues. (MedlinePlus)
* **Iron Absorption:** Vitamin C significantly enhances the absorption of non-heme iron (found in plant-based foods) when consumed together, which is particularly beneficial for individuals following vegetarian or vegan diets and those at risk of iron deficiency. (NIH Office of Dietary Supplements)
* **Cardiovascular Health:** Some research suggests that Vitamin C intake may be associated with improved endothelial function, reduced blood pressure, and a lower risk of cardiovascular disease, although more robust evidence is needed to confirm these effects definitively. (Examine.com)
* **Eye Health:** Studies indicate that Vitamin C, in combination with other antioxidants, may play a role in reducing the risk of age-related macular degeneration (AMD) and cataract progression. (NIH National Eye Institute)
Source for this section: Sources for What is Vitamin C used for?: Jumps to this entry in the sources and references list at the end of the page.
Evidence for Vitamin C's effects comes from various types of studies, including epidemiological observations, clinical trials, and laboratory research.
* **Common Cold:** Numerous controlled trials have investigated Vitamin C's effect on the common cold. A Cochrane review concluded that regular Vitamin C supplementation reduces the duration and severity of colds, but does not prevent their occurrence in the general population. However, it may reduce the incidence of colds in individuals undergoing extreme physical stress (e.g., marathon runners). (Cochrane Review)
* **Scurvy:** Clinical evidence from historical observations and modern case studies unequivocally demonstrates that Vitamin C effectively prevents and treats scurvy, the severe deficiency disease. Recommended daily allowances are based on preventing scurvy. (MedlinePlus)
* **Antioxidant Function:** In vitro and in vivo studies consistently show Vitamin C's potent antioxidant activity, with evidence of its ability to neutralize free radicals and protect against oxidative damage. (PubChem, Linus Pauling Institute)
* **Iron Absorption:** Randomized controlled trials have clearly shown that co-ingestion of Vitamin C with iron-rich plant-based meals significantly increases non-heme iron absorption. (NIH Office of Dietary Supplements)
* **Chronic Disease Prevention:** While observational studies have suggested associations between higher Vitamin C intake and reduced risk of certain chronic diseases like cardiovascular disease and some cancers, large-scale, long-term intervention trials have generally not provided conclusive evidence for a protective effect of Vitamin C supplementation alone in healthy populations. These areas continue to be subjects of active research. (Examine.com, NIH Office of Dietary Supplements)
Source for this section: Sources for How strong is the evidence for Vitamin C?: Jumps to this entry in the sources and references list at the end of the page.
Vitamin C is generally considered safe when taken within typical supplemental ranges, as excess amounts are usually excreted by the body. However, some individuals may experience side effects, particularly at higher doses:
* **Gastrointestinal Issues:** The most common side effects involve the digestive system, including nausea, diarrhea, abdominal cramps, and heartburn. These symptoms are more likely to occur with doses exceeding 2,000 mg per day. (Mayo Clinic)
* **Kidney Stones:** In individuals with a history of kidney stones or those prone to them, very high doses of Vitamin C may increase the risk of oxalate kidney stone formation due to its metabolism into oxalate. (NIH Office of Dietary Supplements)
* **Increased Iron Absorption:** While beneficial for iron-deficient individuals, increased iron absorption from high doses of Vitamin C can be a concern for those with hemochromatosis, a condition causing excessive iron accumulation in the body. (MedlinePlus)
* **False Lab Results:** Very high doses of Vitamin C can interfere with certain medical tests, such as glucose measurements for diabetics and occult blood tests, potentially leading to false results. (DrugBank)
This is educational information, not medical advice — consult a qualified clinician before starting, stopping or combining any compound.
Considerations and warnings associated with Vitamin C include:
* **Kidney Disease:** Individuals with pre-existing kidney disease, particularly those undergoing dialysis, should exercise caution with Vitamin C supplementation, as high doses may worsen kidney function or contribute to oxalate accumulation. (Mayo Clinic)
* **Iron Overload Conditions:** People with conditions like hemochromatosis should avoid high doses of Vitamin C, as it enhances iron absorption, which can exacerbate iron overload. (MedlinePlus)
* **Glucose-6-Phosphate Dehydrogenase Deficiency (G6PD):** In individuals with G6PD deficiency, very high doses of Vitamin C (especially intravenously) have been reported to cause hemolysis (breakdown of red blood cells). (DrugBank)
* **Surgery:** Vitamin C might affect blood sugar levels, which could interfere with blood sugar control during and after surgery. It's advisable to stop Vitamin C supplementation at least two weeks before a scheduled surgery. (Mayo Clinic)
* **Dosage:** While specific dosages for supplementation are not provided as medical advice, it is important to note that the established upper intake level (UL) for adults is 2,000 mg per day, above which the risk of adverse gastrointestinal effects increases. Individual needs vary — talk to a licensed clinician.
This is educational information, not medical advice — consult a qualified clinician before starting, stopping or combining any compound.
While Vitamin C is broadly recognized as safe, certain conditions contraindicate its use or warrant extreme caution:
* **Primary Hemochromatosis:** Due to its ability to enhance iron absorption, Vitamin C supplementation is contraindicated in individuals with primary hemochromatosis, a genetic disorder causing excessive iron accumulation. (MedlinePlus)
* **Kidney Stones (active, severe, recurrent):** In individuals with a significant history of highly recurrent or active oxalate kidney stone formation, particularly those with underlying metabolic predispositions, high doses of Vitamin C may be contraindicated. (Mayo Clinic)
* **Glucose-6-Phosphate Dehydrogenase Deficiency (G6PD):** High-dose intravenous Vitamin C is generally contraindicated in G6PD deficient individuals due to the risk of inducing hemolytic anemia. Oral supplementation at typical doses may be tolerated but caution is advised. (DrugBank)
This is educational information, not medical advice — consult a qualified clinician before starting, stopping or combining any compound.
Certain medications and compounds may interact with Vitamin C, potentially altering their effectiveness or increasing the risk of side effects:
* **Anticoagulants (Blood Thinners):** High doses of Vitamin C might theoretically interfere with the effectiveness of anticoagulant medications like warfarin, although clinical evidence for this interaction is inconsistent. It's advisable to monitor blood clotting parameters if taken concurrently. (Mayo Clinic)
* **Chemotherapy and Radiation Therapy:** There is ongoing debate and inconsistent evidence regarding Vitamin C's interaction with cancer treatments. Some suggest it could reduce the effectiveness of certain chemotherapy drugs or radiation by acting as an antioxidant, while others propose it could be beneficial. Patients undergoing cancer treatment should consult their oncologist before taking high-dose Vitamin C. (NIH National Cancer Institute)
* **Estrogens (e.g., birth control pills, hormone replacement therapy):** Vitamin C may increase estrogen levels or affect the absorption of estrogen-containing medications. (DrugBank)
* **Statins and Niacin (Cholesterol-lowering drugs):** Some studies have suggested that antioxidant supplements, including Vitamin C, when taken with statins and niacin, might counteract the beneficial effects of these drugs on HDL ('good') cholesterol. However, this finding is not consistently replicated across all studies. (Examine.com)
* **Aluminum-containing Antacids:** Vitamin C can increase the absorption of aluminum from antacids, which can be problematic for individuals with kidney issues. (MedlinePlus)
This is educational information, not medical advice — consult a qualified clinician before starting, stopping or combining any compound.
Vitamin C is a water-soluble vitamin and can generally be taken with or without food. Many people choose to take Vitamin C in the morning, often with breakfast, as part of their daily supplement routine. Since it is water-soluble, the body does not store large amounts, and consistent daily intake is beneficial. For individuals who experience gastrointestinal upset, taking Vitamin C with food, especially a meal, may help mitigate these effects. Splitting larger daily doses into two or more smaller doses throughout the day can also help improve absorption and reduce potential digestive discomfort. (MedlinePlus, NIH Office of Dietary Supplements)
Source for this section: Sources for When should you take Vitamin C?: Jumps to this entry in the sources and references list at the end of the page.
Put it into practice
Reading about Vitamin C is the first step — DoseRoutine helps you act on it. These free tools turn what you just learned into a routine.
What interacts with Vitamin C?
| Interacts with | Severity | Type | What happens | What to do |
|---|---|---|---|---|
| Iron (ferrous bisglycinate) | Complementary | Compound pairConfidence: theoretical | Vitamin C increases absorption of non-heme (supplement) iron.Source pending | Fine to take together; no need to separate. |
| Any vitamin + medication | Note | Category ruleConfidence: theoretical | Certain vitamins interact with specific medications (e.g., vitamin K with blood thinners).Source pending | Specific pairs are checked against a licensed source; confirm with your provider. |
Frequently asked questions about Vitamin C
While Vitamin C does not consistently prevent the common cold in the general population, regular supplementation may help reduce the duration and severity of cold symptoms. It has shown more consistent preventive effects in individuals undergoing extreme physical stress. (Cochrane Review)
Excellent food sources of Vitamin C include citrus fruits (oranges, grapefruits), berries (strawberries, blueberries), bell peppers (especially red and yellow), kiwi, broccoli, leafy green vegetables, and tomatoes. (NIH Office of Dietary Supplements)
Yes, while the body generally excretes excess Vitamin C, very high doses (typically above 2,000 mg per day) can lead to gastrointestinal side effects such as diarrhea, nausea, and stomach cramps. In some individuals, high doses may also increase the risk of kidney stone formation. (Mayo Clinic)
Yes, Vitamin C significantly enhances the absorption of non-heme iron (iron from plant sources). This can be particularly beneficial for individuals following vegetarian or vegan diets and those at risk of iron deficiency. (NIH Office of Dietary Supplements)
Yes. Vitamin C is crucial for skin health because it is essential for the production of collagen, a protein that provides structure and elasticity to the skin. It also acts as an antioxidant, protecting skin cells from damage. (MedlinePlus)
Vitamin C is a vitamin, and interactions are possible with prescriptions, hormones, peptides and other supplements in the same routine. Because Vitamin C is usually taken in the morning, most avoidable conflicts come from what else lands in that same window. Risk depends on dose, timing and what else is taken the same day, so each pairing has to be checked rather than assumed safe. The free checker at https://doseroutine.com/interaction-checker covers Vitamin C with no sign-up.
Vitamin C is typically taken in the morning. Ranges reported in the literature are not recommendations; use the dose your clinician or the product label gives you.
Combining a vitamin like Vitamin C with TRT is usually a question of labs rather than a blanket yes or no: the ester, injection interval and any aromatase inhibitor all change the answer. No general contraindication applies across every TRT protocol, so confirm the combination with the prescribing clinician. See the free TRT interaction reference: https://doseroutine.com/trt-supplement-interactions
Each peptide class carries its own profile against Vitamin C: a healing peptide raises different questions than a GLP-1 agonist or a growth-hormone secretagogue. Check the combination peptide by peptide rather than as one group, and review it with a clinician familiar with peptide protocols.
Published frequency for Vitamin C varies by protocol and formulation, so the label or prescription is what sets it. It is typically taken in the morning. Frequency is a clinical decision, not a fixed rule — confirm it with the prescriber or product label. Comparison of apps that keep a schedule like this: https://doseroutine.com/best-dose-tracking-apps
The effect of a missed dose of Vitamin C depends on the protocol and formulation you are on. Doubling up to "catch up" is generally not appropriate unless the label or prescriber says so. Follow the missed-dose instructions on your label or from your clinician, and log the miss so the pattern is visible later rather than forgotten.
For Vitamin C the useful record is the dose, the time it was actually taken, and what else was taken in the same window. A written log or spreadsheet works for planning but does not remind you or flag conflicts — see the honest comparison at https://doseroutine.com/vs/spreadsheet and the wider roundup at https://doseroutine.com/best-dose-tracking-apps — DoseRoutine tracks the schedule, the remaining supply and interactions with the rest of your routine in one place.
The Cochrane review pooled trials using regular vitamin C supplementation of 200 mg/day or more, most commonly 1–2 g/day. Route reported: Oral. Frequency reported: Once daily to divided doses across the pooled trials. These are amounts documented in the cited studies and labels for Vitamin C — they are reported for reference, not a recommendation. Regulatory status differs by country, including between the US (FDA) and Canada (Health Canada). Confirm any amount with a licensed clinician before you take it.
Which studies looked at Vitamin C?
Peer-reviewed research indexed in PubMed. Each entry links to the original record.
- 1.Vitamin C for preventing and treating the common cold(opens PubMed in a new tab)Cochrane Database Syst Rev · 2013 · PMID 23440782 · https://pubmed.ncbi.nlm.nih.gov/23440782/
Sources cited on this page
Specific documents referenced by the numbered markers above. Each number matches the marker in the text.
- NIH Office of Dietary Supplements(opens in a new tab)National Institutes of Health · ods.od.nih.gov/factsheets/VitaminC-Consumer/
- PubChem CID 54670067(opens in a new tab)National Center for Biotechnology Information · pubchem.ncbi.nlm.nih.gov/compound/54670067
Verify at
Publisher search links for Vitamin C. These are places to check the information — they are not citations, so they are not numbered.
- Cochrane Library(publisher search, opens in a new tab)Cochrane · publisher search
- DrugBank(publisher search, opens in a new tab)DrugBank Online · publisher search
- Examine.com(publisher search, opens in a new tab)Examine.com · publisher search
- Linus Pauling Institute(publisher search, opens in a new tab)Oregon State University · publisher search
- Mayo Clinic(publisher search, opens in a new tab)Mayo Clinic · publisher search
- NIH Office of Dietary Supplements(publisher search, opens in a new tab)National Institutes of Health · publisher search
- PubMed literature search(publisher search, opens in a new tab)National Library of Medicine · publisher search
- DailyMed labeling archive(publisher search, opens in a new tab)U.S. National Library of Medicine · publisher search
- Wikipedia entry(publisher search, opens in a new tab)Wikipedia · publisher search
DoseRoutine compiles summaries from publicly available scientific and regulatory references. Always verify important decisions with a licensed clinician. How we source and review this information.
What is the short answer on Vitamin C?
Plain-text summary, safe to quote verbatim:
Vitamin C, also known as ascorbic acid, is an essential water-soluble vitamin that plays a crucial role in numerous physiological functions. As an antioxidant, it helps protect cells from damage caused by free radicals. Research on Vitamin C focuses on immune function, heart and circulatory health, and tissue recovery.
Source: DoseRoutine — https://doseroutine.com/library/vitamin-c
Vitamin C cheat sheet
DoseRoutine cheat sheet · Vitamin
Vitamin C
Vitamin C, also known as ascorbic acid, is an essential water-soluble vitamin that plays a crucial role in numerous physiological functions. As an antioxidant, it helps protect cells from damage caused by free radicals.
Evidence
Moderate
Covered by a systematic review, without regulatory approval.
Studied range
The Cochrane review pooled trials using regular vitamin C supplementation of 200 mg/day or more, most commonly 1–2 g/day
Route
Oral
Frequency studied
Once daily to divided doses across the pooled trials
Half-life
Plasma ascorbate half-life is on the order of hours, though tissue stores are replenished with regular intake
Timing
in the morning
Storage
Room temperature, away from moisture and light
Not FDA-approvedOTC supplementAvailable over the counter in the US as a dietary supplementThe Cochrane review found regular supplementation did not reduce cold incidence in the general population but modestly shortened cold durationImmuneCardiovascularRecovery
Key references
Studied ranges, not dosing advice. Not medical advice — talk to a clinician. doseroutine.com/library/vitamin-c
Cite this page
Using this in an article, AI answer, or research note? Please attribute:
DoseRoutine. (2026). Vitamin C — Overview, Benefits & Side Effects. Retrieved from https://doseroutine.com/library/vitamin-c
What compounds are similar to Vitamin C?
Others in the vitamin category or studied for the same goals.
Which goals is Vitamin C used for?
Other compounds studied for the same benefits as Vitamin C.
Continue exploring
See every compound DoseRoutine catalogs for these goals.