Vitamin C Overview
? The amount of high quality evidence. The more evidence, the more we can trust the results.
? 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.
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
Strong 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).
Minor 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
Minor 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.
Minor 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.
Minor 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)
Minor 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.
Minor Mixed and weak influences on lipid peroxidation, but a possible reduction exists
Minor 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
More evidence suggests no significant effect than a possible protective effect, although the latter is possible
No significant influence of Vitamin C supplementation on HbA1c levels
No significant influence on HDL cholesterol
No significant alterations seen in inflammatory cytokines associated with Vitamin C supplementation
Mixed evidence across studies. Overall, there may be a modest reduction in fasting insulin levels, though more evidence is needed.
No significant alterations in LDL cholesterol seen with Vitamin C supplementation
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
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.
No significant influence on total cholesterol seems apparent with vitamin C supplementation
No significant influence on fasting or postprandial triglycerides seems apparent with Vitamin C
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.
Minor 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
Minor An increase in antioxidant enzymes have been noted in elderly persons
Minor 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.
Minor 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
Minor A possible reduction in C-Reactive Protein exists with Vitamin C supplementation
Minor A decrease in fatigue has been noted in obese adults given Vitamin C in conjunction with exercise
Minor 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.
Minor 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.
Minor An increase in microcirculation has been noted secondary to increased blood flow, thought to be a general property of antioxidants
Minor A possible reduction in muscle soreness the day after exercise may result when preloading exercise with Vitamin C
Minor The rate of percieved exertion in obese adults appears to be attenuated with Vitamin C supplementation
Minor An improvement in mood has been noted in hospitalized persons
Minor Vaginal bacterial infections are somewhat treatable with directly applied (via silicon coated tablets), as Vitamin C exerts some antioxidant effects against those bacterial strains
No significant influence on aerobic exercise performance
No apparent effect on body weight over the course of 4 months.
No significant influences on DNA damage
Highly mixed interactions with the exercise:oxidation axis with Vitamin C, with both increases and decreases being noted. Unlikely to have a reliable role
No significant influence on fat oxidation
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.
No significant influence on heart palpitations
No significant influence on insulin sensitivity
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.
No significant influence on the oxidation rates of LDL cholesterol
No significant influence on pre-eclampsia risk
No significant influence on the risk of cataracts
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.
No significant influence on spontaneous birthing
Insufficient evidence to support a role
There's generally insufficient evidence to discern which cold symptoms vitamin C may affect.
Does not appear to have a role in altering VO2 max
Vitamin C does not appear to have a weight reducing effect
Notable There was a notable decrease in one study, but more research is needed to tell how reliable this effect is.
Minor Attenuation of impairment due to either acute hyperglycemia or elevated free fatty acid levels
Minor Seemed to attenuate the impairment due to acute hyperglycemia, but more research is needed.
No statistically significant effect of 200, 500 and 1000 mg/d for 14 days on postprandial levels.
Higher than control group at some points post-surgery, but not statistically significant.
No trials have found compelling evidence that oral or intravenous vitamin C improves the signs or symptoms of COVID-19.
No difference from 500 mg/d after 3 months of supplementation in type 2 diabetes patients (within-group).
Unclear effect after taking 1 g/d for 4 months.
No difference compared with placebo after taking 6 g/d for 4 weeks.
Unclear if there was an effect of vitamin C compared with placebo in ultramarathon runners.
No apparent difference compared with placebo in response to ultramarathon running.
Nonsignificant increase compared with placebo in response to ultramarathon running.
Possible large reduction due to 7 days of taking 1.5 g/d, however, pre-supplementation measurements weren't taken.
1.5 g/d didn't lead to a significant difference compared with placebo in response to ultramarathon running.
No notable change in estimated glomerular filtration rate (eGFR) in type 2 diabetics over the course of 4 months.
1 g/d for 4 months showed no effect in type 2 diabetic patients.
No notable change in AST, ALT, GGT, or ALP in type 2 diabetics over the course of 4 months.
1.5 g/d didn't lead to a significant difference compared with placebo in response to ultramarathon running.
1.5 g/d didn't lead to a significant difference compared with placebo in response to ultramarathon running.
1.5 g/d didn't lead to a significant difference compared with placebo in response to ultramarathon running.
Supplementation of 1.5 g/d didn't alter the increase in response to ultramarathon running compared with placebo.
No notable change in response to surgery-induced cortisol increases.
Two weeks of 2 g per day didn't alter plasma vitamin E levels.
No apparent effect when used acutely before exercise with a cycle ergometer.
No significant influence on the symptoms of osteoarthritis
It's simply not clear from one study and a small, non-significant reduction.
Possibly attenuates an increase from extreme exercise but it's unclear and especially unclear for other circumstances.
Source: https://examine.com/supplements/vitamin-c/
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