Vitamin C Overview

Vitamin C Overview

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 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 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 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
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 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 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 Minor Low See all 8 studies

Mixed and weak influences on lipid peroxidation, but a possible reduction exists

grade-b 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 - High See all 6 studies

More evidence suggests no significant effect than a possible protective effect, although the latter is possible

grade-b - Very High See all 10 studies

No significant influence of Vitamin C supplementation on HbA1c levels

grade-b - Very High See all 10 studies

No significant influence on HDL cholesterol

grade-b - Very High See all 5 studies

No significant alterations seen in inflammatory cytokines associated with Vitamin C supplementation

grade-b - - 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 - Very High See all 9 studies

No significant alterations in LDL cholesterol seen with Vitamin C supplementation

grade-b - 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 - 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 - Very High See all 13 studies

No significant influence on total cholesterol seems apparent with vitamin C supplementation

grade-b - Very High See all 12 studies

No significant influence on fasting or postprandial triglycerides seems apparent with Vitamin C

grade-b - 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 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 Minor Very High See 2 studies

An increase in antioxidant enzymes have been noted in elderly persons

grade-c 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 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 Minor Very High See all 5 studies

A possible reduction in C-Reactive Protein exists with Vitamin C supplementation

grade-c Minor - See study

A decrease in fatigue has been noted in obese adults given Vitamin C in conjunction with exercise

grade-c 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 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 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 Minor - See study

A possible reduction in muscle soreness the day after exercise may result when preloading exercise with Vitamin C

grade-c 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 Minor - See study

An improvement in mood has been noted in hospitalized persons

grade-c 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 - Very High See all 5 studies

No significant influence on aerobic exercise performance

grade-c - Very High See all 3 studies

No apparent effect on body weight over the course of 4 months.

grade-c - Very High See 2 studies

No significant influences on DNA damage

grade-c - - See study grade-c - - 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 - Very High See 2 studies

No significant influence on fat oxidation

grade-c - 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 - - See study

No significant influence on heart palpitations

grade-c - - See study

No significant influence on insulin sensitivity

grade-c - 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 - - See study grade-c - Very High See all 3 studies

No significant influence on the oxidation rates of LDL cholesterol

grade-c - - See study grade-c - - See study

No significant influence on pre-eclampsia risk

grade-c - - See study

No significant influence on the risk of cataracts

grade-c - - See study grade-c - 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 - - See study grade-c - - See study

No significant influence on spontaneous birthing

grade-c - - See study

Insufficient evidence to support a role

grade-c - Moderate See all 5 studies

There's generally insufficient evidence to discern which cold symptoms vitamin C may affect.

grade-c - - See study

Does not appear to have a role in altering VO2 max

grade-c - Very High See all 4 studies

Vitamin C does not appear to have a weight reducing effect

grade-d 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 Minor High See all 3 studies

Attenuation of impairment due to either acute hyperglycemia or elevated free fatty acid levels

grade-d Minor - See study

Seemed to attenuate the impairment due to acute hyperglycemia, but more research is needed.

grade-d - - See study

No statistically significant effect of 200, 500 and 1000 mg/d for 14 days on postprandial levels.

grade-d - - See study

Higher than control group at some points post-surgery, but not statistically significant.

grade-d - - See study grade-d - Very High See 2 studies

No trials have found compelling evidence that oral or intravenous vitamin C improves the signs or symptoms of COVID-19.

grade-d - - See study

No difference from 500 mg/d after 3 months of supplementation in type 2 diabetes patients (within-group).

grade-d - - See study

Unclear effect after taking 1 g/d for 4 months.

grade-d - - See study

No difference compared with placebo after taking 6 g/d for 4 weeks.

grade-d - - See study

Unclear if there was an effect of vitamin C compared with placebo in ultramarathon runners.

grade-d - - See study

No apparent difference compared with placebo in response to ultramarathon running.

grade-d - - See study

Nonsignificant increase compared with placebo in response to ultramarathon running.

grade-d - - See study

Possible large reduction due to 7 days of taking 1.5 g/d, however, pre-supplementation measurements weren't taken.

grade-d - - See study

1.5 g/d didn't lead to a significant difference compared with placebo in response to ultramarathon running.

grade-d - - See study

No notable change in estimated glomerular filtration rate (eGFR) in type 2 diabetics over the course of 4 months.

grade-d - - See study

1 g/d for 4 months showed no effect in type 2 diabetic patients.

grade-d - - See study

No notable change in AST, ALT, GGT, or ALP in type 2 diabetics over the course of 4 months.

grade-d - - See study

1.5 g/d didn't lead to a significant difference compared with placebo in response to ultramarathon running.

grade-d
- See study

1.5 g/d didn't lead to a significant difference compared with placebo in response to ultramarathon running.

grade-d - - See study

1.5 g/d didn't lead to a significant difference compared with placebo in response to ultramarathon running.

grade-d - - See study

Supplementation of 1.5 g/d didn't alter the increase in response to ultramarathon running compared with placebo.

grade-d - - See study

No notable change in response to surgery-induced cortisol increases.

grade-d - - See study

Two weeks of 2 g per day didn't alter plasma vitamin E levels.

grade-d - - See study

No apparent effect when used acutely before exercise with a cycle ergometer.

grade-d - - See study

No significant influence on the symptoms of osteoarthritis

grade-d - - See study grade-d - - See study

It's simply not clear from one study and a small, non-significant reduction.

grade-d - Low See all 3 studies

Possibly attenuates an increase from extreme exercise but it's unclear and especially unclear for other circumstances.

Vitamin C Overview

Source: https://examine.com/supplements/vitamin-c/

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