Vitamin C
Research reviewed: Up until 03/2026
Vitamin C is a dietary supplement with 3 published peer-reviewed studies involving 2,821 participants, researched for Cognitive Health, Common Cold, Immune Function.
Evidence at a Glance
Strength is scored by study design, sample size, study type, and outcomes
Cognitive Health
ModerateCommon Cold
ModerateImmune Function
ModerateResearch Visualised
Visual breakdown of the clinical data.
Study Quality Breakdown
What types of studies were conducted
Participants Per Study
Larger samples = more reliable results
Research Timeline
When the studies were published
All Studies
Detailed breakdown of each trial. Click to expand.
Cognitive Health
To determine the effects of vitamin C supplementation on mental vitality (specifically attention, work motivation, engagement, and cognitive performance) in healthy young adults with inadequate vitamin C levels
Study Type
Randomised, double-blind, placebo-controlled trial (RCT arm of a two-part study)
Purpose
To determine the effects of vitamin C supplementation on mental vitality (specifically attention, work motivation, engagement, and cognitive performance) in healthy young adults with inadequate vitamin C levels
Dose
1,000 mg/day oral vitamin C (2 × 500 mg) or placebo
Participants
46 healthy young adults aged 20–39 years with inadequate serum vitamin C
Duration
4 weeks
Results
Compared to placebo, vitamin C supplementation significantly increased subjective attention, meaning participants felt more focused and mentally sharp in daily life. Work absorption was also significantly improved in the vitamin C group. In the Stroop colour-word test (a well-validated neuropsychological test that measures selective attention, cognitive flexibility, and information processing speed by requiring participants to name the ink colour of colour words printed in contradictory colours e.g., the word 'RED' printed in blue), participants in the vitamin C group performed significantly better than the placebo group), indicating an improvement in cognitive capacity, not just subjective perception. A trend toward reduced fatigue was also observed (p = 0.06). No significant effects on mood, stress, or depression were found.
Common Cold
To compare the effect of vitamin C supplementation on mild versus severe common cold symptoms across all available individual RCTs that measured both total duration and symptom severity, to determine whether vitamin C selectively benefits the most severe stage of illness.
Study Type
Systematic pooled analysis of randomised, double-blind, placebo-controlled trials (15 comparisons from 10 individual RCTs, each ≥1 g/day vitamin C)
Purpose
To compare the effect of vitamin C supplementation on mild versus severe common cold symptoms across all available individual RCTs that measured both total duration and symptom severity, to determine whether vitamin C selectively benefits the most severe stage of illness.
Dose
1-3 g/day oral vitamin C (regular supplementation)
Participants
The trials in this group included 2736 participants, with a total of 4437 common cold episodes observed during the follow-up
Duration
Varied by trial (each measured during cold episodes)
Results
Across all 15 comparisons, vitamin C significantly decreased overall common cold severity by 15%.In the five comparisons that directly compared mild vs. severe symptoms, vitamin C had a significantly greater benefit on the duration of severe symptoms than on mild symptoms, suggesting that vitamin C specifically shortens the worst and most debilitating phase of a cold, rather than the mild residual stages. Vitamin C had no significant effect on mild symptom duration in this subset.
Immune Function
To determine whether daily vitamin C supplementation reduces the rate, duration, or severity of upper respiratory tract infections (URTIs — infections of the nose, throat and airways, such as the common cold) in adolescent competitive swimmers who are under heavy physical training stress.
Study Type
Randomised, double-blind, placebo-controlled trial
Purpose
To determine whether daily vitamin C supplementation reduces the rate, duration, or severity of upper respiratory tract infections (URTIs — infections of the nose, throat and airways, such as the common cold) in adolescent competitive swimmers who are under heavy physical training stress.
Dose
1,000 mg/day oral vitamin C (2 × 500 mg tablets) or placebo
Participants
39 competitive young swimmers with an average age of 14 years
Duration
3 winter months (the cold and flu season)
Results
In male swimmers, vitamin C significantly shortened the duration of URTIs (upper respiratory tract infections—common colds and throat infections) by 47%, meaning their illnesses lasted about half as long, and it also significantly reduced how severe the symptoms were. However, there was no significant effect in female swimmers for either duration or severity. While infections were 22% shorter across the whole group, this was not significant because the effects differed between males and females. Vitamin C also did not reduce the number of infections (incidence). Overall, results of the study showed that, vitamin C helped male athletes under heavy training recover faster and feel less sick, but didn’t have the same effect in females.
Frequently Asked Questions
Common questions about Vitamin C research
There are currently 3 peer-reviewed studies on Vitamin C (Vitamin C), involving 2,821 total participants. Research covers Cognitive Health, Common Cold, Immune Function. The overall evidence strength is rated as Strong.
The evidence is currently rated as "Strong Evidence". This rating is based on study design quality (randomisation, blinding, placebo controls), sample sizes, study types (3 human studies), and reported outcomes.
Vitamin C has been researched for: Cognitive Health, Common Cold, Immune Function. Each area has its own body of evidence which you can explore in the study breakdowns above.
Yes, 3 out of 3 studies are human trials. Human trials carry more weight in our evidence scoring system.
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