vitamin C

Vitamin C – forms, functions & research

Vitamin C is one of the most commonly supplemented nutrients. Although it is probably best known for its importance to immunity, vitamin C research has revealed multiple other functions within the body.

In the 1920s, vitamin C was first identified by the prospective Nobel laureate Albert Szent-Györgyi from Szeged University in Hungary, who unravelled the role of this essential vitamin for the treatment and prevention of scurvy resulting from vitamin C deficiency.

Before its discovery, around 50% of sailors developed scurvy, a condition now recognised as associated with vitamin C deficiency. It was noted that scurvy could be ameliorated by the consumption of citrus fruits, especially limes, during sea voyages and so lemon or lime juice became part of sailors’ daily rations.

Vitamin C is water soluble, which is an important factor in its function. It is also known as ascorbate or ascorbic acid.1

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Functions of vitamin C

Antioxidant: One of the most powerful functions of vitamin C is as a water-soluble antioxidant (i.e. a reducing agent). When vitamin C reduces (or quenches) free radicals, it becomes oxidised itself. However, it is able to be recycled back to its reduced form by bioflavonoids and glutathione and is therefore described as being able to be oxidised reversibly. The biological role of vitamin C is related to both its antioxidant function and involvement in a multitude of both enzymatic and non-enzymatic processes. Because of its ability to donate electrons, ascorbic acid scavenges reactive oxygen species as well as singlet oxygen. High tissue levels of ascorbate provide substantial antioxidant protection where free radicals are encountered. This antioxidant activity is one of the main properties that makes vitamin C protective for cardiovascular and cognitive health.2,3

Immune support: Vitamin C has multiple effects on the immune system and has been shown to be supportive for a number of different immune cells. Leukocytes including lymphocytes can actively accumulate vitamin C against a concentration gradient demonstrating the importance of vitamin C in these cells. Vitamin C has functional as well as developmental effects on immune cells. In fact, vitamin C has a key role in both innate and adaptive immune responses.1,4

Natural Killer Cells – in clinical studies, vitamin C treatment of healthy subjects promoted and enhanced natural killer cell activities.

Monocytes/macrophages – it has been shown that monocytes contain a high concentration of vitamin C suggesting the regulatory role of this vitamin in monocyte and macrophage functions. In support, an in vitro study revealed that intracellular accumulation of pharmacologic vitamin C concentrations could effectively inhibit apoptotic pathways in human monocytes. Vitamin C may also regulate distinct genes expressed in human macrophages, which are induced by the presence of lipopolysaccharide (found on the cell wall of gram-negative bacteria). In vitro studies have demonstrated that vitamin C application to monocytes derived from human whole blood diminished secretion of pro-inflammatory cytokines such as IL-6 and tumour necrosis factor (TNF)-α. These studies demonstrate the wide effect vitamin C has on macrophages and monocytes alone, not only supporting but also modulating immune function and inflammation.

Neutrophils – the exposure of neutrophils to oxidants inhibits their motility, which is related to oxidation of membrane lipids affecting cell membrane fluidity. In order to protect themselves from oxidative damage, neutrophils accumulate millimolar (mM) concentrations of vitamin C, resulting in improved cellular motility and migration in response of chemotactic stimuli and, subsequently, in enhanced phagocytosis of microbes.

Antimicrobial: Not only does vitamin C protect from pathogens by supporting immune function but it also acts directly as an antimicrobial. It is known that several bacteria can ferment vitamin C, whereas the presence of this vitamin exposes other species to oxidative stress, which may result in bacterial growth inhibition. The potent antibacterial effects of vitamin C are, at least in part, due to its low pH.5

Vitamin C research shows that it:

  • inhibits the growth of Staphylococcus aureus and Streptococci even under neutral pH conditions
  • has potent growth-inhibitory effects against multi-drug resistant (MDR) bacteria such as MRSA and proven synergistic effects with natural or synthetic antibiotic compounds, this could open novel avenues for combatting infections with emerging MDR bacterial species
  • also acts on viruses, parasites, and fungi.

Energy: Vitamin C is also essential for normal energy production by supporting mitochondrial function. It is needed for two dioxygenase enzymes involved in the biosynthesis of carnitine, an essential cofactor in the transport of long-chain fatty acids into the mitochondria. It thus plays an important role in the production of energy via beta-oxidation as impaired carnitine metabolism, including due to insufficient vitamin C supply, can be responsible for weakness or muscle aching.6

In one vitamin c research study, twenty obese adults received an oral dose of either 500mg of vitamin C or a placebo daily for four weeks. Ratings of perceived exertion during moderate exercise and general fatigue scores were significantly decreased in subjects receiving vitamin C. In another study, 44 workers who received an oral dose of 6g vitamin C daily for two weeks reported lower perceived fatigue and exhibited significantly increased blood vitamin C. These findings were confirmed when vitamin C was provided by the intravenous route, a non-physiological but relevant route of administration for research or medical purposes. In a randomised trial, 141 office workers aged 20–49 years received 10g vitamin C or a placebo in one intravenous injection. Fatigue scores two hours and one day after intervention were significantly lower in the vitamin C-treated group and especially in those who had the lowest baseline serum vitamin C.

Collagen synthesis: Vitamin C is essential for the formation of collagen. Specifically, vitamin C has been shown to stabilise collagen mRNA, thus increasing collagen protein synthesis for repair of the damaged skin. Vitamin C acts as a co-factor for the proline and lysine hydroxylases that stabilise the collagen molecule tertiary structure, and it also promotes collagen gene expression. In the skin, collagen formation is carried out mostly by the fibroblasts in the dermis, resulting in the generation of the basement membrane and dermal collagen matrix.7

Preclinical vitamin c studies demonstrated that vitamin C has the potential to accelerate bone healing after a fracture, increase type I collagen synthesis, and reduce oxidative stress parameters. No adverse effects were reported with vitamin C supplementation in either animal models or human participants; thus, oral vitamin C appears to be a safe supplement but lacks clinical evidence compared with controls. Because of the limited number of human studies, it was concluded that further clinical investigations are needed before vitamin C is recommended as a post injury supplement.7



There are many functions and benefits to health of vitamin C but does it have any effect on mortality? Epidemiological studies have shown that vitamin C status is associated with a reduced incidence of death in certain populations. In the EPIC-Norfolk prospective population study, plasma concentration of ascorbic acid was inversely related to mortality from all-causes as well as from cardiovascular disease and ischaemic heart disease. While a study based on an NHANES II database found an inverse relationship between dying from any cause and low ascorbic acid in men, there was no association in women. In research looking at the elderly population, vitamin C concentration was shown to be inversely associated with subsequent mortality in both males and females while in another study ascorbic acid concentration was inversely associated with mortality from stroke but not from coronary heart disease.1

Cardiovascular health

It is suggested that supplementation with vitamin C reduces hyperglycaemia and lowers blood pressure in people with hypertension by enhancing the formation of prostaglandin E1, prostacyclin and endothelial nitric oxide in addition to restoring essential fatty acid metabolism to normal and enhancing the formation of lipoxin A4, a potent anti-inflammatory, vasodilator and antioxidant. These actions are in addition to the ability of vitamin C to function as an antioxidant.1–3

It is well established that vitamin C inhibits oxidation of LDL-protein, thereby reducing the risk of atherosclerosis, but the cardiovascular outcomes related to this action and other actions of vitamin C are not fully understood. Studies have linked vitamin C to improvements in lipid profiles, arterial stiffness, and endothelial function. Overall, current research suggests that vitamin C deficiency is associated with a higher risk of mortality from CVD and that vitamin C may slightly improve endothelial function and lipid profiles in some groups, especially those with low plasma vitamin C levels.

In an NHANES II study, serum vitamin C was inversely related with the prevalence of coronary heart disease and stroke. In cross-sectional studies, blood pressure in middle aged and elderly as well as in young adults was found to be inversely associated with blood vitamin C.1


Vitamin C has long been associated with supporting immune function and therefore preventing or reducing duration of infections. Studies have demonstrated that supplementation with vitamin C appears to be able to both prevent and treat respiratory and systemic infections. Prophylactic prevention of infection requires dietary vitamin C intakes that provide at least adequate (i.e. 100-200 mg/day), to optimise cell and tissue levels. In contrast, treatment of established infections requires significantly higher (gram) doses of the vitamin to compensate for the increased inflammatory response and metabolic demand. Controlled trials found a statistically significant dose-response, for the duration of common cold symptoms, with up to 6-8 g/day of vitamin C. The negative findings of some therapeutic common cold studies might be explained by the low doses of 3-4 g/day of vitamin C. A further three controlled trials found that vitamin C prevented pneumonia.4,5,8


Vitamin C plays an important role in maintaining skin health and can promote the differentiation of keratinocytes and decrease melanin synthesis, leading to antioxidant protection against UV-induced photo-damage. Normal skin needs high concentrations of vitamin C, which plays many roles in the skin, including the formation of the skin barrier and collagen in the dermis, the ability to counteract skin oxidation, and the modulation of cell signal pathways of cell growth and differentiation.9

Research has shown that vitamin C has been effective for:

  • acne scars – improves skin hardness, smoothness, and post-inflammatory pigmentation
  • allergic contact dermatitis – reduces the sensitivity to ap-phenylenediamine (PPD)-containing hair dye
  • psoriatic – supports normal keratinocytes
  • genital herpes – improves immunity and natural defences and reduces the persistence of HPV infection
  • vitiligo – increases hyperpigmentation at pigment diminished spots6

Vitamin C sources

Natural sources of vitamin C include citrus fruits, kiwi, mango, strawberries, papaya, tomatoes, green leafy vegetables, and broccoli. Interestingly, the vast majority of vertebrates can synthesise vitamin C from glucose, but a few mammals, including guinea pigs and humans, have lost this ability due to a lack of the enzyme L-glucono-γ-lactone oxidase, which is necessary for the synthesis of vitamin C in vivo. Therefore, humans need to obtain vitamin C from diet.2

Key Takeaways

  • Whilst vitamin C’s main function is as an antioxidant, it also has important roles in many enzymatic and non-enzymatic reactions.
  • Vitamin C supports immune function by upregulating immune cells. Vitamin C has been associated with prevention and reduced duration of respiratory tract infections.
  • Vitamin C also possesses anti-microbial properties by inhibiting the growth of certain bacteria including Staphylococcus, Streptococci spp. and MRSA resistant bacteria. In addition, it can inhibit fungi and virus replication.
  • Vitamin C supports normal energy production by regulating enzymes which are involved in burning fat for energy by the mitochondria.
  • Vitamin C has been shown to be protective against cardiovascular disease and hypertension partly due to its antioxidant capability but also by supporting blood vessel function and modulating inflammation.
  • Vitamin C plays an important role in maintaining skin health and can promote the differentiation of keratinocytes and decrease melanin synthesis, leading to antioxidant protection against UV-induced photo-damage. Normal skin needs high concentrations of vitamin C, which plays many roles in the skin, including the formation of the skin barrier and collagen in the dermis, the ability to counteract skin oxidation, and the modulation of cell signal pathways of cell growth and differentiation.

If you have questions regarding the topics that have been raised, or any other health matters, please do contact our team of Nutritional Therapists.
01684 310099


  1. (PDF) Vitamin C and Disease: Insights from the Evolutionary Perspective | Csaba Tóth – Accessed February 25, 2020.
  2. Ashor AW, Siervo M, Lara J, Oggioni C, Afshar S, Mathers JC. Effect of vitamin C and vitamin e supplementation on endothelial function: A systematic review and meta-analysis of randomised controlled trials. Br J Nutr. 2015;113(8):1182-1194. doi:10.1017/S0007114515000227
  3. Ashor AW, Lara J, Mathers JC, Siervo M. Effect of vitamin C on endothelial function in health and disease: A systematic review and meta-analysis of randomised controlled trials. Atherosclerosis. 2014;235(1):9-20. doi:10.1016/j.atherosclerosis.2014.04.004
  4. Carr AC, Maggini S. Vitamin C and immune function. Nutrients. 2017;9(11). doi:10.3390/nu9111211
  5. Mousavi S, Bereswill S, Heimesaat MM. Immunomodulatory and antimicrobial effects of vitamin C. Eur J Microbiol Immunol. 2019;9(3):73-79. doi:10.1556/1886.2019.00016
  6. Bendich A, Machlin LJ, Scandurra O, Burton GW, Wayner DDM. The antioxidant role of vitamin C. Adv Free Radic Biol Med. 1986;2(2):419-444. doi:10.1016/S8755-9668(86)80021-7
  7. Pullar JM, Carr AC, Vissers MCM. The roles of vitamin C in skin health. Nutrients. 2017;9(8). doi:10.3390/nu9080866
  8. Hemilä H. Vitamin C and infections. Nutrients. 2017;9(4). doi:10.3390/nu9040339
  9. Wang K, Jiang H, Li W, Qiang M, Dong T, Li H. Role of vitamin C in skin diseases. Front Physiol. 2018;9(JUL). doi:10.3389/fphys.2018.00819

Last updated on 23rd February 2023 by cytoffice


35 thoughts on “Vitamin C – forms, functions & research

  1. Hi there can you tell me which vitamin c product you recommend,I have the Cytoplan 1,000 mg because we want a large dose,unfortunately it burns both my husband and me,we get sore throats and a burning sensation.
    I wondered about liposomal,what would you recommend please.
    Diana Burrows.

    1. Hi Diana,

      I would recommend either Cherry C or Organic Vitamin C – both of which are food forms of Vitamin C and very gentle and effective. You could take 1 capsule up to 3 times a day for round the clock Vitamin C protection at this time.


    2. Hi there,
      I got the Cytoplan vitamin C 1000mg,but unfortunately I experience side effects like constipation.What could posible be the reason for it?
      Is it 1000mg too high dose?
      Thank you very much.

      1. Hi Siyana,

        I wouldn’t think so, in general vitamin C has the opposite effect but everyone can react differently to supplements, vitamin C is taken often up to 5g per day and maintains within tolerable limits. I am afraid I would suggest seeing a nutritional therapist to further investigate.


          1. You can take Vitamin C 1-2 times daily. If you choose one of our wholefood or food state vitamin C supplements, you do not need to take them with food, but we would recommend ascorbic acid is taken with a meal.

      1. HI Candelaria – this will depend upon any specific health concerns you may have, and how much you might be getting through diet – as well as the form of Vitamin C you would like to supplement with. Wholefood forms of Vitamin C, such as those from acerola cherry include natural bioflavonoids and associated food factors, and will stay in your body for longer than synthetic forms, and therefore doses of 200-400mg are appropriate for a healthy individual. You can get vitamin C through foods such as leafy vegetables, tomatoes, citrus fruit and sweet potato.

  2. Very informative, my vague knowledge of vitamin C was that it helped when I had a cold! In the past I have taken vitamin C from other company’s brands and got diarrhoea, but since taking Cherry C have had no contrary effects. I’m very pleased with it so will continue with it. I only take one a day, but guess this is probably enough? Many thanks, Eileen

  3. Hi,
    I have a hiatus hernia and take the vitamin c that is stomach friendly with the mineral element to it eg. calcium, magnesium etc.
    I have heard that this type of vitamin c is not as effective as the simple ascorbate acid. I would like to know your views on this, especially with regard to coronovirus. For instance, do you need to take more of the stomach friendly type to get the same effect as the ascorbate acid?

    1. Hi Mary,

      It is usually best to take a vitamin C, which additionally contains naturally occurring bioflavonoids which support the function of vit C and help to recycle it as an antioxidant. Calcium ascorbate is not always considered the best form as you are taking in excess calcium which in some people can be an issue. Chery C is much gentler on the stomach as is not is ascorbic acid form but a food form with naturally occurring bioflavonoids therefore I generally recommend this one if people want gentle action on stomach.


  4. Are Cytoplan considering a liposomal/cell active vitamin c supplement at any point in the future? Currently taking Cherry C. Thanks

    1. Hi Marie,

      Thank you for your comment.

      No, as although there is some evidence for liposomal vitamin C use, vitamin C by its own virtue is a water soluble antioxidant therefore we are not supportive of the use of liposomal vitamin C.


    1. Hi – this is a very broad question. It really depends on the level of intake you are ingesting from diet, the level you ae supplementing and your individual needs. If you can let us have more information I can help advise on a safe level for long term use, if indeed you need to take it long term. As a rule 200-400mg/day of a food based Vitamin C product is both safe and effective for everyone – please email me:

  5. Is there any different between natural vitamin c from vegetables and that from vitamin c supplement tablet?

    1. Hello – There are many different types of vitamin C supplements and they are not all made equally. Many supplements (especially cheaper ones) are in the form of ascorbic acid which is poorly absorbed and can irritate the digestive system. Vitamin C in food is provided alongside other nutrients such as bioflavonoids which support the function of vitamin C. Our vitamin C (such as FoodState) is in the same form it is found in food and therefore comes with naturally occurring bioflavonoids and is well absorbed and tolerated. It also has the advantage of being in higher levels that can generally be obtained form eating the food itself (also remember that nutrients quantity of food is dependent on soil content, farming, storage and transport methods, so less vitamin C can be present than is expected).

    1. Hi Kirsty – Vitamin C supports collagen production and degradation of collagen is associated with scarring. I would recommend 1-2g per day, make sure it is in a complex with naturally occurring bioflavonoids. You could also try a skin product which contains phytonutrients, beta glucans and vitamins and minerals that support skin health such a zinc, selenium, iodine, biotin and B5 (CytoProtect Hair, Skin and Nails).


  6. How many does of vitamin c is recommend daily and for the skin problem ,how can I use it so solve the skin problem

    1. Hi – people’s needs vary. If you have inflammation then you will need more than most people. On average including dietary sources I would look to ingest a total of around 800mg/day from food and food source material. If your diet is high in sugar and carbohydrates you might need more. Vitamin C is beneficial to skin as it is a precursor to collagen and aids the turnover and repair of new healthy skin tissue It is also anti-inflammatory and anti-histamine.,

    1. Hello – to help support your endothelial function and in turn support healthy blood pressure, you should ensure you are getting great levels of key nutrients such as the B Vitamins, particularly B6, B12 and folate which play a role in methylation, Vitamin C, Vitamin D and Magnesium. The latter two are more difficult to obtain through diet so it might be prudent to take them in supplement form. Other nutrients that can help to support healthy blood pressure include CoEnzyme Q10, a potent antioxidant and the Omega 3 fatty acids, EPA and DHA – which you can obtain from eating oily fish or a suitable supplement. Increasing your intake of plant foods can also help to support your blood blood pressure so aiming for 6-8 portions of a range of colours of fruit and vegetables daily to obtain a range of polyphenols.

  7. Hi
    I have been diagnosed of genital HPV for some months now without treatment. How can Vitamin C be of help. I used to take it for my hypersensitivity to cold.

    1. Hi Tilda – Taking vitamin C can help to increase immunological activity to reduce the persistence of the HPV virus, and studies have demonstrated that persistent HPV infection was found to be lower among women reporting an increased intake of Vitamin C. It is worth noting that there is also evidence of other supplements being supportive the resolution of HPV, including Zinc and probiotics, so to discuss the best supplements for you, please do get in touch with our team of nutritional therapists at

    1. Hi there, you can take Vitamin C 1-2 times daily. If you choose one of our wholefood or food state vitamin C supplements, you do not need to take them with food, but we would recommend ascorbic acid is taken with a meal.

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