Vitamin C in COVID-19 Prevention Leo Goldstein , May 31, 2020

This is not medical advice. This is a petition to federal and state governments to urgently publish recommendations for vitamin C intake as a prevention measure against COVID-19.


Can vitamin C prevent or alleviate symptoms of acute respiratory tract infections, including COVID-19? (Gorton & Jarvis, 1999) reported 85% decrease of cold and flu symptoms in the test group taking vitamin C, compared with the control group, not taking vitamin C. The test group took vitamin C prophylactically and over the course of disease at 3,000 mg per day (1,000 mg x 3), and an increased dose of 6,000 mg (1,000 mg x 6, hourly) on the first day of symptoms onset. This specific regimen is important: taking a moderate amount of vitamin C prophylactically and during illness, and a larger dose on the first day of symptoms onset.

There is a caveat. The dosage in this study is 1.5-2 times higher than what doctors feel comfortable recommending to the public, as far as I see. Nevertheless, the research reviewed below supports the conclusion that 1.5-2 times lower doses help against broad class of ARTI, including colds and flu, although expectably less. COVID-19 is an acute respiratory tract infection (ARTI). The reasonable assumption is that what helps against multiple prior viral ARTI would help against COVID-19.

Vitamin C Role in the Immune System

Vitamin C does not prevent infection, but it helps the immune system combat it. It has been shown to alleviate symptoms, sometimes to the point where symptoms are not detectable. Thus, a person can feel as if s/he never got sick, since no symptoms ever presented, and may count this as having prevented the illness.

Vitamin C, at its normal level 70 μmol/L, is a necessary part of the immune system.  Excess vitamin C intake (over 200 mg/day) is normally excreted in urine. But when a body experiences physiological stress, it consumes the vitamin C present in the blood and thus, needs an increased intake (Hemilä, Vitamin C and Infections, 2017). All existing studies agree on this point. Observations have shown that in such conditions even many grams of vitamin C per day are neither excreted nor accumulate in blood.

(Hemilä & Chalker, 2019) listed several studies, showing that vitamin C levels drop in patients hospitalized with acute respiratory infections to less than 10-35% of the normal level. (Carr, 2017) found that all ICU patients in one hospital had less than on third of the normal vitamin C level.

The rationale behind discovered Vitamin C supplementation

When a person gets a viral respiratory infection, the body starts fighting it using the vitamin C present in the blood. That decreases vitamin C levels in the blood, impairing the immune system, even before the symptoms appear. But if it regularly receives extra vitamin C, it stops excreting it, but consumes in fighting the infection. In the most successful regimens (Ran, 2018), symptoms are used as a signal that the body requires even more vitamin C in order to maintain normal vitamin C blood levels while consuming more of it in fighting the infection. That justifies increased intake of it on the first symptomatic day and until the body overcomes the virus. This time might be shorter than the period for which symptoms exist. The first symptomatic day might have a special significance, possibly because it is when the body have not produced enough antibodies specific to the virus.


The human body has natural safety valves for vitamin C. First, excess of it is removed in urine. Second, it typically causes diarrhea before getting close to potentially dangerous levels.

(National Institute of Health, 2020) confirms safety of vitamin C:

Vitamin C has low toxicity and is not believed to cause serious adverse effects at high intakes. The most common complaints are diarrhea, nausea, abdominal cramps, and other gastrointestinal disturbances due to the osmotic effect of unabsorbed vitamin C in the gastrointestinal tract.

Possible Vitamin C Regimen

This is a possible Vitamin C regimen against COVID-19, for adults.

Some doctors recommend taking the higher dose only on the first day of symptoms onset. The dose is for an average 70 kg person. Those weighing much more or less should adjust proportionately. Older and non-healthy persons (i.e., the most at-risk group) should consult their physicians

Possible contra-indications: some kidney diseases, chemotherapy and radiation treatments, cholesterol lowering drugs,  diabetes in postmenopausal women (National Institute of Health, 2020). For other people, diarrhea is a sign to decrease or stop taking vitamin C.

It is not expected to completely protect against the Wuhan coronavirus or to approach the effectiveness of HCQ + Zn prophylaxis.

I remind that this is not medical advice, but a starting point for CDC/NIH/FDA and state governments to develop the medical advice.  Follow your doctor’s recommendations.

Vitamin C Controversies and Misconceptions

Some confusion surrounds the use of vitamin C because different amounts are used for different purposes and produce different results. The officially recommended minimum intake of vitamin C 75-90 mg per day is just that – the minimum, established long ago to prevent scurvy. Many people exceed this amount simply by eating ordinary food; a medium orange contains 70 mg of vitamin C.

Studies with vitamin C supplementation of less than 1 g/day have shown little or no effect on respiratory infections. This was a cause of the confusion among medical professions. At such amounts, “control” group’s vitamin C intake was not controlled and might have exceeded the amounts taken by the intervention group. Also, low level vitamin C supplementation might provide benefits too low to detect. That might have caused confusion among medical professionals. Further, most studies gave vitamin C either prophylactically or during illness, but not both (Hemilä, Vitamin C and Infections, 2017).

On the high end, mega-doses of vitamin C (like tens of grams per day), delivered intravenously in hospital settings, is successfully used in treatment of many serious diseases and conditions, including late stages of severe cases of COVID-19. They are used for patients with sepsis (Kashiouris, 2020) and acute respiratory distress syndrome. Such doses and associated treatments are beyond the scope of this article.

Thus, this review is only concerned with vitamin C doses of 1 – 3 g/day prophylactically, and 3 – 6 g/day during ARTI. Such doses have been shown helpful in easing ARTI, and safe for almost all people.

Studies Review

Peer Reviewed Papers

(Hemilä, 2017) is a meta-analysis of multiple studies. It concludes that vitamin C is helpful against many infections, especially the common cold. The study suggests a linear dose – effect function up to 6-8 g/day.

(Hemilä & Chalker, 2019) is another meta-analysis. In 12 trials, totaling 1766 patients , vitamin C, given during the time of treatment, reduced ICU stays by an average of 7.8%. The vitamin C doses were relatively small, 1-3 g/day. (In four studies, higher doses were used, but those studies were either excluded from the meta-analysis (Dingchao 1994) or given very low weight in the calculations (Tanako 2000, Fowler 2014, Zabet 2016)). In this studies vitamin C was given too little too late.

(Marik & Hooper, 2017) explains that vitamin C acts like a “stress hormone”. Most vertebrates synthesize their vitamin C and increase its production during physiological stress. Humans, as well as primates and guinea pigs, are exceptions to this rule. Therefore, we need to obtain vitamin C from food or supplements, and we may need to increase our intake in times of physiological stress.

(Colunga Biancatelli, Berill, & Marik, 2019) explains concepts behind vitamin C antiviral benefits. Unfortunately, they cite a 2013 review by Hemilä et al., which did not find benefits of vitamin C supplementation, as explained above. The more recent meta-analysis (Hemilä, Vitamin C and Infections, 2017) has firmly established evidence of such benefits.

(Ran, 2018) is a review, showing benefits of taking daily vitamin C supplements before and increasing the dosage when common cold occurs. It proposes a regimen of taking 1 g/day prophylactically while healthy and 3-4 g/day while having a cold.

Non peer reviewed sources

Beneficial effects of vitamin C supplementation have been reported for

Elderly people with acute respiratory infections

Recurrent acute respiratory distress syndrome

Reducing the severity and duration of the common cold

Reducing the length of hospital stay and symptoms in elderly patients with pneumonia

Reducing the duration of mechanical ventilation in people in ICU

Preventing the common cold in people who are vitamin C deficient

Preventing the incidence of pneumonia in people who are vitamin C deficient.

Studies have shown that excretion of vitamin C is decreased during infections, such as the common cold, suggesting that more is utilized during times of need.

COVID-19: Prevention and Treatment, Vitamin C (, Michelle Fauver, Ph.D.):

If you choose to supplement with vitamin C as a preventive, you might want to start with 2 grams a day administered orally

To use vitamin C supplementation as a treatment for colds or flus (remember we still have the flu going around), the best results have been obtained by administering 6-8 g (6,000-8,000 mg) immediately upon appearance of the first symptoms, then continuing that dose daily until the symptoms subside.

8 g/day is likely to cause diarrhea.


  • The effect of prophylactic doses of vitamin C in COVID-19 infection have not been quantified. But even if the effect were small (and there is no reason to think that it is small), when the infection spreads exponentially, it decreases the exponential coefficient. It is a possibly large impact, at a miniscule cost, with almost no risk. Further, vitamin C seems to help the immune system to decrease the viral load even if it does not alleviate the symptoms.
  • Taking vitamin C is not the only helpful prophylactic measure receiving less attention than it deserves.  Another research piece shows similar benefits of cod liver oil, used in this country for hundreds of years, or its equivalent – a diet rich in wild caught salmon or mackerel.
  • Physiological stress is not the same as psychological stress. I do not know whether lockdowns and forced social isolation cause physiological stress.
  • While it is not the role of the federal government to recommend diets and vitamin supplements, Google and Facebook delete and hide information about potentially effective COVID-19 prophylactics and treatment, if it does not come from WHO or a government. Thus, to allow such information to reach the public, the federal government should either rein in Google and Facebook, or itself make the recommendations.
  • I prefer the name Wuhan coronavirus the COVID-19 pathogen. This is where the virus was detected first. The name SARS-CoV-2 is associated with SARS of 2003, which had a much higher mortality ratio. This association is misleading and causes unnecessary panic.
  • To avoid the appearance of bias, I excluded from this review most known enthusiasts of the vitamin C. I also did not rely upon the peer-reviewed Journal of Orthomolecular Medicine, although it is a recognized medical journal, and included in multiple indexes.
  • It is impossible not to mention Linus Pauling in this article. I do not know whether he was right or wrong about vitamin C. It might be that some of his ideas were correct, but explanation and/or clinical recommendations were not.
  • A medical group of Eastern Virginia Medical School, headed by Dr. Paul Marik, has developed and published its own COVID-19 prophylactic regimen, including vitamin C, Zinc, and Quercetin. It is occasionally mentioned in comments on this site.


Carr, A. (2017). Hypovitaminosis C and vitamin C deficiency in critically ill patients despite recommended enteral and parenteral intakes. Critical Care. Retrieved from

Colunga Biancatelli, R. M., Berill, M., & Marik, E. P. (2019). The antiviral properties of vitamin C. Expert Review of Anti-infective Therapy. Retrieved from

Gorton, H., & Jarvis, K. (1999). The effectiveness of vitamin C in preventing and relieving the symptoms of virus-induced respiratory infections. Journal of Manipulative and Physiological Therapeutics. Retrieved from

Hemilä, H. (2017). Vitamin C and Infections. Nutrients. Retrieved from

Hemilä, H., & Chalker, E. (2019). Vitamin C Can Shorten the Length of Stay in the ICU: A Meta-Analysis. Nutrients. Retrieved from

Kashiouris, M. (2020, January 22). The Emerging Role of Vitamin C as a Treatment for Sepsis. Nutrients. Retrieved from

Marik, P. E., & Hooper, M. H. (2017). Vitamin C and Sepsis, Response. The Chest Journal. Retrieved from

National Institute of Health. (2020, February 27). Vitamin C. Fact Sheet for Health Professionals. Retrieved from

Ran, L. (2018). Extra Dose of Vitamin C Based on a Daily Supplementation Shortens the Common Cold: A Meta-Analysis of 9 Randomized Controlled Trials. BioMed Research International. Retrieved from

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