Quick Navigation

Vitamin C

Vitamin C is an essential vitamin with antioxidant properties. It is frequently supplemented to ward off the common cold, though its efficacy is questionable, and likely low.

Our evidence-based analysis on vitamin c features 377 unique references to scientific papers.

Kamal Patel
Research analysis led by and reviewed by the Examine team.
Last Updated:

Summary of Vitamin C

Primary information, health benefits, side effects, usage, and other important details

Vitamin C, or L-ascorbic acid, is a water-soluble essential vitamin. It is a very popular dietary supplement due to its antioxidant properties, safety, and low price.

Vitamin C is often supplemented to reduce the symptoms of the common cold.

However, vitamin C is unable to reduce the frequency of colds in a healthy population. An athlete who frequently undergoes intense physical activity can expect to cut the risk of getting a cold in half. Supplemental vitamin C is able to reduce the duration of a cold by 8-14% in any population, when it is taken as a daily preventative measure, or at the beginning of a cold. Though superloading vitamin C (5-10g daily) is said to be more effective, further research is needed to determine the accuracy of this claim.

Vitamin C is capable of being both an antioxidant and pro-oxidant, depending on what the body needs. This mechanism allows it to serve a variety of functions in the body.

Vitamin C sequesters free radicals in the body. It is replenished by antioxidant enzymes, and is often used as a reference drug in antioxidant research. Vitamin C’s structure allows it to act on neurology and depression, as well as interact with the pancreas and modulate cortisol. Its antioxidant properties mean vitamin C provides neuroprotective effects and benefits for blood flow. By protecting the testes from oxidative stress, vitamin C can also preserve testosterone levels.

💊 Get unbiased supplement information


How to Take

Recommended dosage, active amounts, other details

The Recommended Daily Intake (RDI) of vitamin C is 100-200mg. This is easily attained through the diet, so supplementation of such low doses is usually unnecessary. Higher doses of vitamin C, up to 2,000mg, are used to support the immune system (for athletes) or reduce the duration of the common cold.

Most studies on vitamin C prescribe one dose per day. The claim that taking 2,000mg up to five times a day to optimally reduce cold symptoms is not sufficiently tested and requires more evidence.

Easily stay on top of the latest nutrition research

Become an Examine Member to get access to the latest research. Get 150+ studies summarized for you across 25 different categories every month.

Members also have access to the Examine Study Database of 400+ supplements and their effects on 600+ health outcomes, as well as in-depth research analyses. Understand the whole body of nutrition and supplement evidence at a glance.

Get instant access — start your free 14-day trial

Already a Member? Click here to log in.


Human Effect Matrix

Unlocked for Examine Members

Easily stay on top of the latest nutrition research

Become an Examine Member to get access to the latest research. Get 150+ studies summarized for you across 25 different categories every month.

Members also have access to the Examine Study Database of 400+ supplements and their effects on 600+ health outcomes, as well as in-depth research analyses. Understand the whole body of nutrition and supplement evidence at a glance.

Get instant access — start your free 14-day trial

Already a Member? Click here to log in.


The Human Effect Matrix summarizes human studies to tell you what effects Vitamin C has on your body, how much evidence there is, and how strong these effects are.

Full details are available to Examine Members. Not a Member? Try Examine Membership completely free for two weeks.
Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
Notes
grade-b
Plasma Vitamin C
Strong Very High See all 11 studies
For the purpose of increasing plasma Vitamin C concentrations, orally supplemented Vitamin C appears to be the best decision (second only to intravenous vitamin C).
grade-b
Blood Flow
Minor Very High See all 7 studies
An increase in blood flow is seen in instances of impaired blood flow (smoking, obesity, etc.) which may be due to preservation of nitric oxide function (via reducing oxidation thereof); this is a phenomena general to antioxidants and not unique to Vitamin C
grade-b
Blood glucose
Minor - See all 20 studies
Studies are very mixed, however, there appears to be a modest benefit to fasting glucose in type 2 diabetics. More research is needed before having great confidence in this effect. The vast majority of studies don't treat this outcome as their primary outcome and more glucose-specific research is needed.
grade-b
Cortisol

Minor 		- See all 7 studies
Vitamin C (500-1,500mg daily) appears to be associated with both increases and decreases in exercise-induced cortisol spikes, depending on whether it acts as a prooxidant or antioxidant (respectively). There is no influence on resting cortisol concentrations.
grade-b
General Oxidation
Minor Moderate See all 7 studies
Surprisingly mixed influences on biomarkers of oxidation, with either a decrease or no significant influence the majority of the time (with limited evidence to hint at an increase being possible)
grade-b
Length of Sickness
Minor Moderate See all 26 studies
The evidence suggests that a small (roughly half a day) reduction is found when vitamin C is taken consistently, even when not sick, but not if it's only started once already sick. For other infectious diseases, it's unclear if vitamin C helps.
grade-b
Lipid Peroxidation
Minor Low See all 8 studies
Mixed and weak influences on lipid peroxidation, but a possible reduction exists
grade-b
Muscle Damage
Minor Moderate See all 4 studies
Although not acute, a possible reduction in biomarkers of muscle damage is sometimes noted with antioxidative supplementation which applies to Vitamin C; results are unreliable
grade-b
Exercise-Induced Immune Suppression
- High See all 6 studies
More evidence suggests no significant effect than a possible protective effect, although the latter is possible
grade-b
HbA1c
- Very High See all 10 studies
No significant influence of Vitamin C supplementation on HbA1c levels
grade-b
High-density lipoprotein (HDL)
- Very High See all 10 studies
No significant influence on HDL cholesterol
grade-b
Inflammation
- Very High See all 5 studies
No significant alterations seen in inflammatory cytokines associated with Vitamin C supplementation
grade-b
Insulin
- - See all 11 studies
Mixed evidence across studies. Overall, there may be a modest reduction in fasting insulin levels, though more evidence is needed.
grade-b
Low-density lipoprotein (LDL)
- Very High See all 9 studies
No significant alterations in LDL cholesterol seen with Vitamin C supplementation
grade-b
Protection from Smoking
- High See all 3 studies
There do not appear to be any inherent protective effects of Vitamin C against the oxidative and inflammatory changes associated with cigarette smoking, although the reduction in blood flow may be attenuated somewhat with antioxidants and this applies to Vitamin C
grade-b
Rate of Sickness
- Moderate See all 28 studies
When used as a prophylactic, vitamin C's effects are very inconsistent, and overall it doesn't seem to reliably reduce the risk of getting a common cold. It's possible that those undergoing extreme exercise (a known risk factor for developing colds) see a meaningful reduction in risk, however this is based on much less research and requires further study. It's unclear if other infectious diseases are affected by vitamin C supplementation.
grade-b
Total cholesterol
- Very High See all 13 studies
No significant influence on total cholesterol seems apparent with vitamin C supplementation
grade-b
Triglycerides
- Very High See all 12 studies
No significant influence on fasting or postprandial triglycerides seems apparent with Vitamin C
grade-b
Upper Respiratory Tract Infection Risk
- See all 25 studies
When used as a prophylactic, vitamin C's effects are very inconsistent, and overall it doesn't seem to reliably reduce the risk of getting a common cold. It's possible that those undergoing extreme exercise (a known risk factor for developing colds) see a meaningful reduction in risk, however this is based on much less research and requires further study. It's unclear if other infectious diseases are affected by vitamin C supplementation.
grade-c
Adaptations to Exercise
Minor Moderate See 2 studies
It is thought that, secondary to reducing the rate of muscular damage, that adaptations gained from exercise are attenuated; there is mixed evidence to support this, but is seems possible with antioxidants
grade-c
Anti-Oxidant Enzyme Profile
Minor Very High See 2 studies
An increase in antioxidant enzymes have been noted in elderly persons
grade-c
Blood Pressure
Minor Moderate See all 5 studies
May attenuate the increase due to acute hyperglycemia or over the course of 4 months in type 2 diabetics, though the evidence is mixed and more research is needed.
grade-c
Bone Mineral Density
Minor Very High See 2 studies
The rate of bone mineral density loss over time in elder women appears to be reduced with dietary antioxidants, and as such applies to Vitamin C supplementation. The protective effect is not remarkably large
grade-c
C-Reactive Protein (CRP)
Minor Very High See all 5 studies
A possible reduction in C-Reactive Protein exists with Vitamin C supplementation
grade-c
Fatigue
Minor - See study
A decrease in fatigue has been noted in obese adults given Vitamin C in conjunction with exercise
grade-c
Frequency of Intercourse
Minor - See study
Supplementation of 3,000mg Vitamin C appeared to increase sexual frequency from 4 times monthly to 14 times in non-cohabitating subjects. There was no significant effect on cohabitating subjects. No influence on masturbation frequency.
grade-c
Heart Rate
Minor Moderate See all 5 studies
A decrease in heart rate has been noted in exercising obese adults, a per se effect of Vitamin C on heart rate (rather than secondary to the rate of percieved exertion) seems unlikely.
grade-c
Microcirculation
Minor - See study
An increase in microcirculation has been noted secondary to increased blood flow, thought to be a general property of antioxidants
grade-c
Muscle Soreness
Minor - See study
A possible reduction in muscle soreness the day after exercise may result when preloading exercise with Vitamin C
grade-c
Rating of perceived exertion (RPE)
Minor Very High See all 3 studies
The rate of percieved exertion in obese adults appears to be attenuated with Vitamin C supplementation
grade-c
Subjective Well-Being
Minor - See study
An improvement in mood has been noted in hospitalized persons
grade-c
Symptoms of Bacterial Vaginosis
Minor - See study
Vaginal bacterial infections are somewhat treatable with directly applied (via silicon coated tablets), as Vitamin C exerts some antioxidant effects against those bacterial strains
grade-c
Aerobic Exercise
- Very High See all 5 studies
No significant influence on aerobic exercise performance
grade-c
Body Fat
- Very High See all 3 studies
No apparent effect on body weight over the course of 4 months.
grade-c
DNA Damage
- Very High See 2 studies
No significant influences on DNA damage
grade-c
Depression
- - See study
grade-c
Exercise-Induced Oxidation
- - See 2 studies
Highly mixed interactions with the exercise:oxidation axis with Vitamin C, with both increases and decreases being noted. Unlikely to have a reliable role
grade-c
Fat Oxidation
- Very High See 2 studies
No significant influence on fat oxidation
grade-c
Glycemic Control
- Very High See all 3 studies
Mixed evidence. Significant improvement with 1 g/d in type 2 diabetics, though not accompanied by changes in fasting blood glucose. The other study didn't find a change.
grade-c
Heart Palpitations
- - See study
No significant influence on heart palpitations
grade-c
Insulin Sensitivity
- - See study
No significant influence on insulin sensitivity
grade-c
Interleukin 6
- Low See all 4 studies
Mixed evidence. One study found a significant reduction compared with placebo after 8 weeks supplementation, one study found a non-significant increase in response to ultramarathon running, and one study found no change.
grade-c
Mineral Bioaccumulation
- - See study
grade-c
Oxidation of LDL
- Very High See all 3 studies
No significant influence on the oxidation rates of LDL cholesterol
grade-c
Oxygenation Cost of Exercise
- - See study
grade-c
Pre-Eclampsia Risk
- - See study
No significant influence on pre-eclampsia risk
grade-c
Risk of Cataracts
- - See study
No significant influence on the risk of cataracts
grade-c
Seminal Motility
- - See study
grade-c
Severity of Sickness
- Moderate See all 12 studies
While some research suggests that vitamin C could modestly reduce the amount of time people spend indoors during colds, overall symptom severity doesn't seem to be meaningfully affected. More research is needed to determine its effect on the severity of symptoms.
grade-c
Sperm Quality
- - See study
grade-c
Spontaneous Birth Risk
- - See study
No significant influence on spontaneous birthing
grade-c
Symptoms of Charcot-Marie-Tooth Disease
- - See study
Insufficient evidence to support a role
grade-c
Symptoms of the Common Cold
- Moderate See all 5 studies
There's generally insufficient evidence to discern which cold symptoms vitamin C may affect.
grade-c
VO₂max
- - See study
Does not appear to have a role in altering VO2 max
grade-c
Weight
- Very High See all 4 studies
Vitamin C does not appear to have a weight reducing effect
grade-d
Resistin
Notable - See study
There was a notable decrease in one study, but more research is needed to tell how reliable this effect is.
grade-d
Endothelial Function
Minor High See all 3 studies
Attenuation of impairment due to either acute hyperglycemia or elevated free fatty acid levels
grade-d
Vascular Function
Minor - See study
Seemed to attenuate the impairment due to acute hyperglycemia, but more research is needed.
grade-d
Adiponectin
- - See study
No statistically significant effect of 200, 500 and 1000 mg/d for 14 days on postprandial levels.
grade-d
Adrenocorticotropic Hormone
- - See study
Higher than control group at some points post-surgery, but not statistically significant.
grade-d
Asymmetric dimethylarginine (aka ADMA)
- - See study
grade-d
COVID-19 Severity
- Very High See 2 studies
Two trials have failed to find compelling evidence that oral or intravenous vitamin C improves the signs or symptoms of COVID-19.
grade-d
Creatinine
- - See study
No difference from 500 mg/d after 3 months of supplementation in type 2 diabetes patients (within-group).
grade-d
Fructosamine
- - See study
Unclear effect after taking 1 g/d for 4 months.
grade-d
Glomerular Filtration Rate
- - See study
No difference compared with placebo after taking 6 g/d for 4 weeks.
grade-d
IL-1Ra
- - See study
Unclear if there was an effect of vitamin C compared with placebo in ultramarathon runners.
grade-d
Interferon Gamma
- - See study
No apparent difference compared with placebo in response to ultramarathon running.
grade-d
Interleukin 10
- - See study
Nonsignificant increase compared with placebo in response to ultramarathon running.
grade-d
Interleukin 2
- - See study
Possible large reduction due to 7 days of taking 1.5 g/d, however, pre-supplementation measurements weren't taken.
grade-d
Interleukin 8
- - See study
1.5 g/d didn't lead to a significant difference compared with placebo in response to ultramarathon running.
grade-d
Kidney Function
- - See study
No notable change in estimated glomerular filtration rate (eGFR) in type 2 diabetics over the course of 4 months.
grade-d
Lean Mass
- - See study
1 g/d for 4 months showed no effect in type 2 diabetic patients.
grade-d
Liver Enzymes
- - See study
No notable change in AST, ALT, GGT, or ALP in type 2 diabetics over the course of 4 months.
grade-d
Lymphocyte Count
- - See study
1.5 g/d didn't lead to a significant difference compared with placebo in response to ultramarathon running.
grade-d
Monocyte Count

- See study
1.5 g/d didn't lead to a significant difference compared with placebo in response to ultramarathon running.
grade-d
Natural Killer Cell Content
- - See study
1.5 g/d didn't lead to a significant difference compared with placebo in response to ultramarathon running.
grade-d
Neutrophil Count
- - See study
Supplementation of 1.5 g/d didn't alter the increase in response to ultramarathon running compared with placebo.
grade-d
Osteocalcin
- - See study
No notable change in response to surgery-induced cortisol increases.
grade-d
Plasma Vitamin E
- - See study
Two weeks of 2 g per day didn't alter plasma vitamin E levels.
grade-d
Power Output
- - See study
No apparent effect when used acutely before exercise with a cycle ergometer.
grade-d
Symptoms of Osteoarthritis
- - See study
No significant influence on the symptoms of osteoarthritis
grade-d
TNF-Alpha
- - See study
grade-d
Urea
- - See study
It's simply not clear from one study and a small, non-significant reduction.
grade-d
Uric Acid
- Low See all 3 studies
Possibly attenuates an increase from extreme exercise but it's unclear and especially unclear for other circumstances.

Studies Excluded from Consideration

Stay on top of the latest research

To unlock the full archives of our Study Database and research analyses, become an Examine Member today.

Start your 14-day free trial

Frequently Asked Questions and Articles on Vitamin C

Does vitamin C improve blood sugar control?
We recently added several studies to the vitamin C page regarding blood sugar effects. From existing research, it seems theoretically possible that vitamin C could help improve blood sugar control, but the evidence is quite mixed at this point.
Read full answer to "Does vitamin C improve blood sugar control?"
Are vitamin C supplements bad for your teeth?
Read full answer to "Are vitamin C supplements bad for your teeth?"

Things to Note

Is a Form Of

Primary Function:

Other Functions:

Also Known As

Ascorbic Acid, Ascorbate, 2-oxo-L-threo-hexono-1, 4-lactone-2, 3-enediol, L-ascorbic acid

Do Not Confuse With

L-Threonic Acid (a metabolite)

Goes Well With

  • Zinc and Iron (may enhance absorption)

Caution Notice

  • Superloading vitamin C, particularly via intravenous injections, has repeatedly been demonstrated in case studies to cause oxalate nephrotoxicity. This is treatable (potentially lethal if not treated) and may be a reason to avoid injections of vitamin C if not supervised by a medical doctor.

Get our free 5-day course on the essentials of supplementation.

At Examine, our incentives line up with yours — getting unbiased information. That's why we don’t sell any advertising or supplements.

Join over 250,000 people who have learned about effective versus overrated supplements, tips for buying supplements, and how to combine supplements for safety and efficacy.

Click here to see all 377 references.

  • Get the latest research

    Examine is your partner to better health.

    Get access to the most up-to-date, in-depth research reviews. No industry ties, no sponsors, no bias.

    Try free for 14 days

This page is regularly updated, to include the most recently available clinical trial evidence.

Each member of our research team is required to have no conflicts of interest, including with supplement manufacturers, food companies, and industry funders. The team includes nutrition researchers, registered dietitians, physicians, and pharmacists. We have a strict editorial process.

This page features 377 references. All factual claims are followed by specifically-applicable references. Click here to see the full set of research information and references for Vitamin C.

Examine.com is intended to be used for educational and information purposes only. Examine.com and its Editors do not advocate nutritional supplementation over proper medical advice or treatment and this sentiment will never be expressed through pages hosted under Examine.com. If using any pharmaceuticals or drugs given to you by a doctor or received with a prescription, you must consult with the doctor in question or an equally qualified Health Care Professional prior to using any nutritional supplementation. If undergoing medical therapies, then consult with your respective Therapist or Health Care Professional about possible interactions between your Treatment, any Pharmaceuticals or Drugs being given, and possible nutritional supplements or practices hosted on Examine.com.

Examine.com does not assume liability for any actions undertaken after visiting these pages, and does not assume liability if one misuses supplements. Examine.com and its Editors do not ensure that unforeseen side effects will not occur even at the proper dosages, and thereby does not assume liability for any side effects from supplements or practices hosted under the domain of Examine.com.

Supplements

Articles

Health Topics

Membership Free Trial

Protein Intake Guide + Calculator

How to read a study

Company

Resources

Never miss an update!

Your email is safe with us. We don’t share personal data.

This website is certified by Health On the Net Foundation. Click to verify.