Vitamin C, naturally present in many fruits and vegetables, plays an integral part in both innate and adaptive immune systems. It enhances neutrophil chemotactic response while supporting their role in phagocytosis and killing of microbes by leukocytes.

Vitamin C helps reduce harmful nitrogen-based compounds like nitrosamines and nitrosamides, protecting DNA and keeping cells functioning at their best.

Vitamin C Deficiency

Vitamin C’s reputation as a fighter against sickness is legendary, not only against common cold but also many other conditions like cancer, heart disease and age-related macular degeneration that may benefit from increased consumption of this nutrient.

As soon as you become sick, your blood vitamin C levels decrease due to increased metabolic demand and inflammation. Supplementing with Vitamin C may restore these levels and bolster immunity; however it should be noted that at higher dosages beyond RDA (recommended daily allowance), vitamin C may switch from being an antioxidant into being pro-oxidant, leading to tissue damage.

Even with numerous anecdotal reports about vitamin C’s healing powers, research results remain mixed, with some studies not finding any positive impacts. Much of this variance can be explained by different effects it has on cells and organisms; however, systematic differences in study design may also account for inconsistent findings. Cellular responses may only serve as surrogates for clinical outcomes while immune system response to vitamin C does not always correspond with protection from infection.

However, although some studies have demonstrated benefits in terms of decreased incidence and duration of colds in large population study populations, their findings remain subject to scrutiny due to large sample sizes. Regular vitamin C use did reduce by half the number of cases experienced by physically active people as well as shortening duration, suggesting its potential health-giving properties.

Vitamin C is also necessary for leukocytes in both the innate and adaptive parts of our immune systems to function optimally, modulating production of proinflammatory and antiinflammatory cytokines as well as gene expression of immune cells. Furthermore, macrophages depend on Vitamin C to clear spent neutrophils away from sites of infection thus reducing necrosis, NETosis, cell damage and subsequent necrosis and NETosis.

Studies conducted during the COVID-19 pandemic have indicated that high-dose vitamin C could help protect and treat serious complications related to coronavirus infection, including sepsis and pneumonia. As a result, interest has grown among health practitioners to include this nutrient in prophylactic and treatment protocols; however, definitive outcomes still need to be established to verify these claims.

Antioxidant Activity

Vitamin C is a water-soluble antioxidant molecule, providing protection for biomolecules from damage by free radicals generated during normal metabolism or from exposure to environmental toxins and pollutants. Furthermore, it serves as cofactor in biosynthetic and gene regulatory enzymes.

Vitamin C’s multiple benefits extend to both innate and adaptive immune cell functions, including neutrophil and mast cell functions. Accumulated vitamin C in these phagocytic cells increases their chemotaxis and phagocytosis as well as increasing generation of reactive oxygen species to kill microorganisms [123]. It has also been demonstrated to protect these phagocytic cells from oxidant-induced damage by directly scavenging these harmful molecules while at the same time replenishing glutathione and vitamin E within them [124]. Vitamin C modulates cell signaling pathways by controlling pro-inflammatory transcription factors like nuclear factor kB while at the same time inhibiting pro-inflammatory cytokine interleukin-6 [124].

Clinical studies involving patients suffering from genetic neutrophil disorders such as chronic granulomatous disease (CGD), in which leukocytes generate reactive oxygen species incorrectly, and Chediak-Higashi syndrome (CHS), which disrupts vesicle trafficking, have demonstrated improved ex vivo neutrophil chemotaxis after vitamin C administration, suggesting it may augment their antimicrobial mechanisms.

Preclinical studies have also demonstrated the cytokine-modulating benefits of vitamin C. One such experiment involving Gulo knockout mice treated with 200 mg/kg parenteral vitamin C showed decreased production of pro-inflammatory cytokines such as TNF-a and IL-1 in their lungs while simultaneously decreasing IFN- secretion; supporting this micronutrient’s potential use against severe complications associated with coronavirus infections.

Infections have a tremendous effect on vitamin C levels due to metabolic and inflammatory demands, but supplementing with it has proven effective at alleviating existing infections. Studies have demonstrated its beneficial properties by stimulating B- and T-cell differentiation and proliferation with its gene regulatory activities, increasing phagocytosis by neutrophils, inhibiting necrosis/NETosis by neutrophils, decreasing sequestration by macrophages of neutrophils for sequestration by bacteria, which in turn may prevent excessive inflammation responses that cause tissue damage due to excessive inflammation responses.

White Blood Cells

Vitamin C plays an essential role in white blood cell function and health. This includes increasing T-lymphocyte activation and production as well as B-lymphocyte production – two essential elements of cell-mediated immunity. Studies have demonstrated that oral or intravenous supplementation with low gram doses of vitamin C enhances ex vivo lymphocyte proliferation; its effects are further amplified when taken alongside vitamins A and E.

Vitamin C assists the immune response by increasing neutrophil phagocytosis and production of reactive oxygen species (ROS). ROS play an essential role in killing microbes; however, neutrophils often accumulate excessively after being stimulated with soluble stimulants or upon phagocytosis [118]. Vitamin C works against this effect by supporting reverse oxidative burst and protecting membrane integrity [119].

Vitamin C has also been demonstrated to stimulate chemotaxis of peripheral blood monocytes in vitro and bronchoalveolar epithelial cells in preclinical studies, possibly due to its direct activation of chemokines that promote leukocyte migration into inflammation sites. Furthermore, numerous clinical studies have confirmed its efficacy against recurrent infections by intravenously administering vitamin C supplements [120].

Vitamin C’s primary role in respiratory tract health lies in its ability to improve epithelial barrier functions. Animal studies have demonstrated this with vitamin C treatment increasing lung fluid clearance, increasing permeability of the bronchoalveolar epithelial barrier and decreasing sequestration of neutrophils at inflammatory loci; additionally it was shown that sepsis-induced respiratory injury reversed with vitamin C therapy [72-73].

Health conditions that compromise circulation and tissue vitamin C levels include tobacco smoking, which has been found to significantly decrease its status, leading to reduced resistance against infection among its users. Furthermore, ageing reduces plasma and leukocyte vitamin C levels leading to an increased risk of infectious diseases in elderly populations [234].

Natural Killer Cells

Natural killer cells form part of your innate immune system, which provides your first line of defense against pathogens and cancer. Physical barriers like skin and mucous membranes keep germs at bay while select immune cells respond quickly when threats get past these barriers. Similar to other white blood cells, NK cells patrol the body looking out for signs of diseased or infected cells; when they detect them they release proteins called cytokines which direct other cells to attack and eliminate it.

NK cells belong to the lymphocyte family of cells known as lymphocytes, such as T and B cells, yet differ significantly by being part of your innate immunity system rather than adaptive immunity system – meaning they can quickly destroy potential threats without prior exposure to certain pathogens or viruses. They’re best known for killing virally infected cells, while they may even detect and prevent early stages of cancer development.

Human NK cells can be divided into two subsets, CD56bright and CD56dim. The former are more prevalent in lymph tissue and associated organs, such as liver and lungs, while CD56dim are found more widespread throughout tissues like brain tissue and the immune system. Both subsets contain numerous activating and inhibitory killer Ig-like receptors which bind with target cells that express either MHC class I molecules or non-MHC class I molecules for activating NK cells.

The CD56dim subset can be found primarily in the spleen and bone marrow, where it primarily comprises non-cytolytic NK cells with wide ranges of cytotoxic receptors that engage other cell types (dendritic cells and T cells) for engagement purposes, including tumor cell destruction as well as inflammation responses. These cells also play a role in supporting immune-inflammatory reactions.

NK cells are an integral component of your innate immune system and play an essential role in overall health and wellbeing. If they stop working correctly, however, they could lead to autoimmune diseases – where your immune system attacks healthy cells rather than pathogens or cancerous ones.