Vitamin C and the immune system, from cells to infections
What it found
Vitamin C helps immune cells work, and low levels are linked to more infections.
The authors say 100 to 200 mg a day keeps levels adequate, while treating an infection may need gram doses.
What they found
Studies in people
Infections
The authors report that vitamin C at 200 mg or more a day eased the severity and duration of the common cold. In pneumonia patients, low-dose vitamin C cut hospital stay by 19% and higher doses by 36%.
Animal and lab studies
Clearing spent cells
Vitamin C helps neutrophils die off cleanly and be cleared away, which limits tissue damage. In vitamin C-deficient mice, neutrophils did not do this and instead died in a way that can harm tissue.
Studies in people and animals
Barrier and skin
Vitamin C builds up in skin cells and helps collagen formation. In people, taking vitamin C increased its uptake into skin cells and the skin's ability to mop up oxidants.
Neutrophil movement
Neutrophils are white blood cells that rush to infections. In guinea pigs lacking vitamin C, their movement was impaired, and in people with low vitamin C, supplements improved it by about 20%.
Killing microbes
Neutrophils from scorbutic guinea pigs had a severely impaired ability to kill microbes. In people with low vitamin C, a dietary supplement boosted the generation of microbe-killing oxidants by 20%.
Lymphocytes
In lab tests, vitamin C helped B and T cells multiply and mature. Some human studies found more lymphocyte activity with vitamin C, but others did not.
What the authors conclude
“Overall, vitamin C appears to exert a multitude of beneficial effects on cellular functions of both the innate and adaptive immune system.”
Also in their conclusions
- They conclude that vitamin C is necessary for the immune system to mount and sustain an adequate response against pathogens while avoiding excessive damage to the host.
- They say that preventing infection requires dietary vitamin C intakes that provide at least adequate, if not saturating plasma levels (i.e., 100–200 mg/day), which optimize cell and tissue levels.
- They advise that treatment of established infections requires significantly higher (gram) doses of the vitamin to compensate for the increased metabolic demand.
How it was done
The authors wanted to bring together the many roles vitamin C plays in the immune system, including barrier integrity and white blood cell function, and to look at what this means for infections and for people who do not get enough.
They reviewed more than half a century of research on vitamin C and immunity, covering lab studies, animal studies and human studies, and looked at how vitamin C affects immune cells, infections and conditions linked to low vitamin C.
What it can’t tell you
- Many of the findings come from animals or cells, so they cannot show exactly what happens in people.
- It is not yet certain to what extent improved white blood cell movement in the lab translates into better immune function in the body.
- The review cannot prove that vitamin C prevents or treats infections in every person, because the studies varied in dose, duration and the people studied.
Who paid
- Conflicts
- S.M. is employed by Bayer Consumer Care Ltd., a manufacturer of multivitamins, and wrote the section on ‘Vitamin C insufficiency conditions’. A.C.C. has received funding, as a Key Opinion Leader, from Bayer Consumer Care Ltd.
- Authors work at
- University of Otago, New Zealand
The paper
- Title
- Vitamin C and Immune Function
- Type
- ReviewThe authors read earlier studies and describe what they found. It isn’t a new study.
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Cite
- Carr AC, Maggini S (2017). Vitamin C and Immune Function. Nutrients. doi:10.3390/nu9111211Free full textPubMed 29099763DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error