My name is Dr. Chris Pallia, and I am an orthopedic surgeon based out of San Diego, California and I am affiliated with the Synergy Orthopedic Specialists Medical Group.
In my prior 2 blogs on immune system function, I covered the benefits of Vitamin D and Zinc on immune function and reduction of infection. This final blog on the topic of immune function will highlight all the essential functions and benefits of Vitamin C. All the information here is referenced in published peer-reviewed research articles.
Vitamin C works in many ways to enhance the immune function, influencing and enhancing many bodily systems. Included below is summary chart. The essence is: it protects the skin and enhances its healing, acts as an antioxidant, enhances immune cell motility and phagocytosis (engulfing foreign particles), enhances microbial killing, and controls excessive inflammation.
Here's more detail: Given that vitamin C is essentially involved in collagen biosynthesis and repair, the lack of ascorbic acid impairs integrity of basement membranes, mucosal epithelia, and connective tissues, which is causative for the devastating periodontal disease observed in scurvy. Furthermore, the vitamin is required for proper wound healing and bone development, both of which linked to the role of ascorbic acid in collagen synthesis. Other biochemical functions of vitamin C include carnitine synthesis, redox-reactions, production of adrenal steroids and catecholamines, metabolism of amino acids and cholesterol, and iron absorption [5, 27, 28].
In addition, the observations that vitamin C concentrations in immune cells such as leukocytes are 10- to 100-fold higher than those measured in the plasma [6] and the fact that these cells accumulate vitamin C against a concentration gradient further underline the immunological importance of vitamin C [42, 43] and support its role as crucial player in various aspects of immune cell functions, such as immune cell proliferation and differentiation [17, 44–46], besides its anti-inflammatory properties [47, 48]. Moreover, the newly characterized hydroxylase enzymes, which regulate the activity of the hypoxia-inducible factors (HIF), gene transcription, and cell signaling of immune cells, require vitamin C as a cofactor for optimal activity [49–52].
In order to protect themselves from oxidative damage, neutrophils accumulate millimolar (mM) concentrations of vitamin C [65], resulting in improved cellular motility and migration in response of chemotactic stimuli [66] and, subsequently, in enhanced phagocytosis of microbes and generation of reactive oxygen species (ROS) [17].
For a few vertebrate species including humans having lost their capacities to synthesize vitamin C themselves during evolution, the uptake of this essential compound from external sources is mandatory in order to prevent from vitamin deficient conditions resulting in severe morbidities such as scurvy. However, vitamin C supplementation is well tolerated and safe, given a virtual absent risk of intoxication with normal renal function, given that vitamin C is water-soluble and excessive amounts can be easily excreted in the urine.
Vitamin C supports epithelial barrier function against pathogens and promotes the oxidant scavenging activity of the skin, thereby potentially protecting against environmental oxidative stress.
Prophylactic prevention of 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. In contrast, treatment of established infections requires significantly higher (gram) doses of the vitamin to compensate for the increased inflammatory response and metabolic demand.
Patients with acute respiratory infections, such as pulmonary tuberculosis and pneumonia, have decreased plasma vitamin C concentrations relative to control subjects [245]. Administration of vitamin C to patients with acute respiratory infections returns their plasma vitamin C levels to normal and ameliorates the severity of the respiratory symptoms [246]. Cases of acute lung infections have shown rapid clearance of chest X-rays following administration of intravenous vitamin C [247,248]. This vitamin C-dependent clearance of neutrophils from infected lungs could conceivably be due to enhanced apoptosis and subsequent phagocytosis and clearance of the spent neutrophils by macrophages [73].
Meta-analysis has indicated that vitamin C supplementation with doses of 200 mg or more daily is effective in ameliorating the severity and duration of the common cold, and the incidence of the common cold if also exposed to physical stress [249].
In other pneumonia patients, low-dose vitamin C (0.25–0.8 g/day) reduced the hospital stay by 19% compared with no vitamin C supplementation, whereas the higher-dose group (0.5–1.6 g/day) reduced the duration by 36% [255]. There was also a positive effect on the normalization of chest X-ray, temperature, and erythrocyte sedimentation rate [255].
High-dose intravenous VC has also been successfully used in the treatment of 50 moderate to severe COVID-19 patients in China. The doses used varied between 10 g and 20 g per day, given over a period of 8–10 h. Additional Vitamin C bolus may be required among patients in critical conditions. The oxygenation index was improving in real time and all the patients eventually cured and were discharged [18]. In fact, high-dose Vitamin C has been clinically used for several decades and a recent NIH expert panel document states clearly that this regimen (1.5 g/kg body weight) is safe and without major adverse events [19].
So, I think it is easy to conclude that for optimum human immune function for the protection against bacterial and viral invasion, make sure you have adequate amounts of Vitamins D, Zinc, and Vitamin C through appropriate dietary intake or supplementation.
References:
Immunomodulatory and Antimicrobial Effects of Vitamin C.
Mousavi S, Bereswill S, Heimesaat MM.
Eur J Microbiol Immunol (Bp). 2019 Aug 16;9(3):73-79. doi: 10.1556/1886.2019.00016. eCollection 2019 Oct 3.
Vitamin C and Immune Function.
Carr AC, Maggini S.
Nutrients. 2017 Nov 3;9(11):1211.
Can early and high intravenous dose of vitamin C prevent and treat coronavirus disease 2019 (COVID-19)?
Cheng RZ.
Med Drug Discov. 2020 Mar;5:100028.