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How Vitamin C Supports Immunity

Updated: Aug 31, 2022


Part 1

Various immune cells are highly dependent on vitamin C for their ability to fight viruses and other infectious pathogens.

For example, vitamin C helps neutrophils (the most abundant immune cells in the bloodstream) generate respiratory bursts that essentially blow-up viruses on contact.

Vitamin C also protects neutrophils from free radical damage that would otherwise destroy them during a respiratory burst assault against a virus.

Vitamin C helps minimize the secretion of NET’s (neutrophil extravascular nets), which often trigger a life-threatening cytokine storm in acute respiratory distress syndrome caused by certain viruses, bacteria, and other pathogens.

Vitamin C also helps immune cells migrate to the site where viruses are present in the body, enabling them to mount an attack.

So, ensuring that your intake of vitamin C is optimal each day is one more proactive step you can take to preserve your immune function and your overall wellbeing.


Bozonet SM and Carr AC. The role of physiological vitamin C concentrations on key functions of neutrophils isolated from healthy individuals. Nutrients June 2019.


More About Vitamin C and Immunity

Here is a direct quote from the 2017 published review on Vitamin C and Immunity, "Vitamin C contributes to immune defense by supporting various cellular functions of both the innate and adaptive immune system".

The innate immune system includes immune cells that require no prompting to kill offending viruses and other disease-promoting bacteria and microbes (germs). Over millions of years of evolution these immune cells, such as Natural Killer Cells, Macrophages, Neutrophils and Dendritic cells, have evolved to seek out and destroy disease-promoting germs (viruses etc.) on contact.

The adaptive immune system involves certain immune cells that ingest the virus (or other disease-promoting germs) and display the germ’s spiky antigens on their own outer surface, which they then present to a group of T-lymphocytes called, T-Helper Cells (or CD4) cells.

Once presented to the T-Helper cells, the T-Helper cells recruit many other immune cells into the fight against the virus or infectious agent. The newly-recruited immune cells, such as the B-lymphocytes and plasma cells, replicate quickly to form a larger army of immune cells to fight the infection. This is why your white blood cell count increases during an infection, as your white blood cells are all-important cells of your body's immune system.

During an infection, both the innate and adaptive immune system consume vitamin C at a much faster rate, and thus, increasing vitamin C intake at the first sign of a cold or respiratory tract infection has been shown to improve outcomes.


2017 Review: Vitamin C and Immune Function


Vitamin C and Immunity: A Few More Important Details

In addition to the effects of vitamin C on immunity mentioned in previous Healthy Lifestyle Boosters, here are several other ways that our immune system depends on adequate vitamin C status to protect us from serious infections:

  1. Vitamin C is required to form the materials that are part of the body’s physical barrier to viruses and other hostile germs, preventing them from penetrating through our skin, our respiratory passageways, our intestinal tract, etc.

  2. Vitamin C accumulates in phagocytic immune cells, such as neutrophils (the most numerous white blood cells in the bloodstream) that ingest, blow up and destroy viruses (and other germs) on contact. Vitamin C enhances the neutrophil's ability to move to the location of the virus (or germ), engulf the virus (or germ) and generate free radicals to blow up the virus (or germ), while also acting as an antioxidant to protect neutrophils from the free radicals they generate to destroy the virus (or germ).

  3. Vitamin C is also needed to encourage damaged neutrophils to commit suicide (apoptosis) so they don’t linger in a dysfunctional state and secrete dangerous NETs (Neutrophil Extravascular Traps), which are known to create the life-threatening cytokine storm in the lungs and other organs.

  4. The role of vitamin C in lymphocytes (another type of white blood cell) is less clear, but it has been shown to enhance maturation and replication of B- and T-cells, likely due to its gene-regulating effects.

As stated in the previous Healthy Lifestyle Booster, we will look at preventive and therapeutic vitamin C doses that have been reported from various published studies, in an upcoming Healthy Lifestyle Booster issue.


2017 Review: Vitamin C and Immune Function


Vitamin C Supplementation: How Much Do You Need?

In the previous Healthy Lifestyle Boosters, I explained the various and critically important ways that vitamin C works to help optimize immune function.

In the abstract of their 2017 review paper, regarding vitamin C and immunity, the researchers conclude, "vitamin C deficiency results in impaired immunity and higher susceptibility to infections. In turn, infections significantly impact on vitamin C levels due to enhanced inflammation and metabolic requirements.

Furthermore, 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, 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."

Their review paper also cites studies where vitamin C was administered to elderly hospitalized patients with pneumonia, showing that the group given vitamin C had a hospital stay that was 36% shorter with objective signs of improvement including normalization of chest X-ray, temperature, and ESR (a blood test for inflammation). The dosage was 500 – 1600 mg of vitamin C per day (not really that high a dosage).


2017 Review: Vitamin C and Immune Function


Vitamin C Absorption and Dosage to Support Immunity

Many people take extra vitamin C each day to boost the function of their immune system. But, how much should you take?

Studies show that 100% of ingested vitamin C is absorbed at doses of up to 200 mg at a time. Ingesting more than 500 mg of vitamin C is somewhat of a waste, as the absorption of vitamin C is highly limited to 500 mg or less from a single dose.

Blood levels of vitamin C peak when taking doses of 200-400 mg at a time. Taking higher doses than this at one time does not increase blood vitamin C levels appreciably. The peak vitamin C blood level from oral intake is 60-80 umol/L.

Keeping your vitamin C blood level above 50 umol/L is considered desirable to help optimize immune function. This can be done by spreading out 500 mg doses of vitamin C throughout the day. For example, taking 500 mg doses of vitamin C, every 4 waking hours. This approach helps to keep blood vitamin C maintained within the optimal range throughout the entire day and is much more effective than taking 1,000 or 2,000 mg of vitamin C as a single dose.


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