Human studies show vitamin C reduces the incidence and severity of various forms of infectious disease.
We’ve heard it all our lives:
Vitamin C fights colds.
That’s partially true.
Some human studies show that taking vitamin C can lessen the severity and duration of the common cold.1
What’s irrefutable is the role that vitamin C plays in maintaining immune function.2-4
The ABCs of Vitamin C
Vitamin C is an essential nutrient in humans.2 Without it we die.
Humans don’t internally produce vitamin C like most animals. It must be obtained from diet or other external sources. Severe vitamin C deficiency—medically known as scurvy2—causes major health problems, including increased susceptibility to infections. 5
Low vitamin C levels are relatively common in the United States. 2,6,7 Diets lacking in fruits and vegetables fail to provide enough vitamin C. Vitamin C is further depleted by smoking, illness, exposure to pollutants, and stress.2 As a water-soluble nutrient, vitamin C can’t be readily stored in the body.
Impact on Infections
In the process of fighting infection, immune cells rapidly use up vitamin C.2
Some studies show that in common infectious illnesses, such as colds, supplemental vitamin C lessens the severity and duration of symptoms.1
In people with acute respiratory infections, like bronchitis or pneumonia, increasing oral dosages of vitamin C can reduce the severity of respiratory symptoms.8 The results can be dramatic. Some studies report rapid clearance on chest x-rays of patients with lung infections, following intravenous vitamin C treatment.9,10
In pneumonia and other serious infections, vitamin C has been shown to reduce symptoms, shorten hospital stay, and lead to more rapid normalization of markers of disease.8,11
Barrier Against Disease
Before viruses, bacteria, and other infectious agents can make us ill, they must invade the body, breaching biological barriers meant to prevent their entry. Our skin and the linings of our respiratory and digestive tracts are protective barriers. Vitamin C is important for the creation and maintenance of these protective-barrier tissues. It’s required for the synthesis of collagen, a structural protein that provides strength and durability to barrier and connective tissues.2
Vitamin C also affects the linings of the airways in lungs, which are prone to infection. In animals with acute lung infection, treatment with vitamin C has been shown to restore barrier function, repairing junctions between cells in the lining of the respiratory tract.12
Helping Immune Cells
Vitamin C supports cells of the immune system, including those most directly involved in response to infections. Neutrophils are the “first responder” immune cells against infections. They are called to infected tissues early in the course of disease. Research has shown that they play important roles in response to viral as well as bacterial infections.13,14
Vitamin C supports neutrophil function by:
Helping neutrophils reach an infection . Early in an infection, neutrophils migrate to the infected tissues. Insufficient vitamin C impedes this process, making it difficult for neutrophils to find the infection.15-17 In a study of participants with inadequate vitamin C status, daily supplementation with vitamin C resulted in a 20% increase in neutrophil migration.18
Helping neutrophils destroy microbes . Once neutrophils encounter an infection, they consume and kill infectious organisms. With vitamin C deficiency, that ability is severely impaired.2 One study showed that increased vitamin C intake, in combination with vitamin E, enhances the ability of neutrophils to devour and kill infectious agents.19
After neutrophils destroy pathogens, they die off and are removed by other cells. This helps resolve inflammation and start the healing process. But a lack of vitamin C can cause neutrophils to die in a way that releases potentially toxic compounds, causing new inflammation and tissue damage that make disease even worse.20,21 Preclinical studies show that adequate vitamin C inhibits this harmful process.22
Lymphocytes are the second most common form of immune cells. They include B cells, T cells, and natural killer cells (NK cells). These cells are an integral part of the immune system’s ability to recognize foreign invaders and mount an attack on them.
Vitamin C promotes growth, maturation, antibody production, and survival of lymphocytes.23-26
WHAT YOU NEED TO KNOW
Vitamin C Helps Fight Infections
Vitamin C strengthens immunity by promoting healthy barrier function to keep out pathogens and supporting optimal function of immune-system cells.
Inadequate levels of vitamin C are not uncommon and can impair immune response. Requirements for vitamin C are increased when the body is fighting infection.
Daily oral intake of vitamin C restores bodily levels and has been shown to improve the function of immune cells, supporting a healthy response to viral and other infections.
Reducing Inflammation
Excessive inflammation initiated by infection causes damage to tissues. Preclinical studies show that vitamin C reduces excessive amounts of pro-inflammatory compounds.22,27,28
Studies in animal models and in humans have demonstrated that oral intake of vitamin C leads to lower levels of histamine, a pro-inflammatory compound which causes symptoms of both infection and allergy.17,29-31
Fighting excessive inflammation is important in wound healing and recovery of tissues following injury. By decreasing pro-inflammatory compounds, vitamin C helps initiate tissue-healing processes.32
Summary
Vitamin C is an essential nutrient that supports healthy immune function. Inadequate levels of vitamin C in the body impair the ability to ward off infectious disease and respond to an infection. Increasing intake of vitamin C corrects some of these impairments. This helps strengthen barrier functions that repel infectious agents and support optimal immune-cell function.
The need for vitamin C increases with acute illness. In animal models and human clinical studies, vitamin C has been shown to reduce incidence and severity of various forms of infectious disease.
References
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Webb AL, Villamor E. Update: effects of antioxidant and non-antioxidant vitamin supplementation on immune function. Nutr Rev. 2007 May;65(5):181-217.
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Fisher BJ, Kraskauskas D, Martin EJ, et al. Mechanisms of attenuation of abdominal sepsis induced acute lung injury by ascorbic acid. Am J Physiol Lung Cell Mol Physiol. 2012 Jul 1;303(1): L20-32.
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Goldschmidt MC, Masin WJ, Brown LR, et al. The effect of ascorbic acid deficiency on leukocyte phagocytosis and killing of actinomyces viscosus. Int J Vitam Nutr Res. 1988;58(3):326-34.
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Adapted from: https://www.lifeextension.com/magazine/2020/8/vitamin-c-role-in-immune-health