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Can Vitamin C Help Combat COVID-19?

For decades, doctors dismissed vitamin C as worthless against the common cold. But could vitamin C help combat COVID-19? Trials are underway!

The Pfizer/BioNTech and Moderna vaccines reduce the likelihood of hospitalization with COVID-19, they don’t provide perfect protection. In particular, the Omicron variant has evolved in a way that allows it to infect vaccinated people. As a result, many individuals would like additional ways to ward off or treat respiratory tract infections. Is there any evidence to suggest that vitamin C could help combat COVID-19?

Reader Asks–Can Vitamin C Combat COVID-19?

Q. For about the first three decades of my life, I routinely had several episodes of the common cold over the winter. Then I heard that vitamin C could serve to prevent colds.

A supplement seemed simple to try, so I did. It worked like magic. I take 500 mg/day, and I have not had a cold for over 40 years.

Is vitamin C still supposed to prevent colds? Could it provide any protection against the COVID variants?

Vitamin C for Respiratory Tract Infections:

A. Vitamin C for colds has been controversial for decades, possibly much longer than you imagine. An article appeared in the Medical Journal of Australia in 1947. It was titled “Vitamin C in the Prevention of Colds.”  Ever since then, doctors have been arguing about how effective this nutrient might be against respiratory tract infections.

A review in Frontiers in Immunology (May 10, 2021) concluded that

“There is strong evidence that vitamin C can shorten the duration of respiratory virus infections.”

The authors also report that people taking high doses of vitamin C may have shorter duration of symptoms associated with COVID-19.

Dr. Linus Pauling and Vitamin C:

Some of the controversy around vitamin C can be traced to Linus Pauling, a scientist in the early 20th century. He is the only person to win two unshared Nobel Prizes, one in his primary field of chemistry and the other for his peace activism.

Dr. Pauling is perhaps best remembered for his advocacy of vitamin C (ascorbic acid). His book, Vitamin C and the Common Cold, generated tremendous controversy within the medical community. While many consumers embraced the idea of taking extra vitamin C during cold season, medical professionals tried hard to debunk the idea that vitamin C supplements had health benefits.

Decades ago, Dr. Franklin Bing wrote this in JAMA (March 1, 1971):

“The many admirers of Linus Pauling will wish that he had not written this book [Vitamin C and the Common Cold]. Here are found, not the guarded statements of a philosopher or scientist seeking truth, but the clear, incisive sentences of an advertiser with something to sell. Unfortunately, many laymen are going to believe the ideas that the author is selling—that ascorbic acid is a completely harmless chemical which will prevent or mollify infectious diseases such as the common cold, if taken in doses of from 1 to 10 gm daily throughout life, and possibly extend that lifetime from two to six years. Actually, when used as recommended by Professor Pauling, neither the safety of all dosage forms, nor the efficacy of ascorbic acid in any dosage form, has been proved.”

To this day, many nutritionists believe that Dr. Pauling duped the American public into taking extra vitamin C. They maintain that most people get all the ascorbic acid they need from their diet. Many insist that a little glass of orange juice or some fruit once in a while will do the trick.

How Common Is Vitamin C Deficiency?

Perhaps Americans are not quite as well nourished as the professionals imagine, however.

According to Dr. Tieraona Low Dog in her book, Fortify Your Life:

“The CDC Second National Report on Biochemical Indicators of Diet and Nutrition in the U.S. Population found that almost 16 million people in the U.S. over the age of six are deficient in vitamin C, taking in less than 30 mg/day—far less than the 75 to 90 mg recommended by the FDA, which itself is far lower than most experts believe is optimal.”

Vitamin C and Respiratory Tract Infections:

A new review suggests that Dr. Pauling may not have been as misguided as many doctors maintain (Nutrients, Dec. 7, 2020).

These authors note that:

“Vitamin C has important anti-inflammatory, immunomodulating, antioxidant, antithrombotic and antiviral properties. The vitamin demonstrates direct virucidal activity and has effector mechanisms in both the innate and adaptive immune systems.”

Did You Know Animals Make Vitamin C?

Most animals make their own vitamin C. For example, a typical goat synthesizes more than 13,000 mg daily. Dogs, cats, lizards, cows and other animals also make their own ascorbic acid.

Primates don’t, so they need to get enough vitamin C from the fruits, vegetables and leaves that they eat. For a gorilla, that comes out to about 4,500 mg a day. So why do humans need only 90 mg per day (man) or 75 mg per day (woman)?

The RDA for Vitamin C vs. Scurvy:

As it turns out, the RDA was set at the relatively low level that can prevent scurvy, a vitamin C deficiency disease. That might not be all there is to the story, though. While early 20th century researchers were excited to find a way to prevent scurvy, Dr. Pauling wanted to know what else the vitamin is doing. At that time, no one imagined we would be looking for a way to help combat COVID-19.

Could Vitamin C Help Against Colds?

Most health professionals believe that vitamin C is worthless against colds. That’s largely because several studies have not shown benefit against “the common cold.”

One problem with such studies is that the researchers have assumed that all colds are created equal. It would be as if doctors who treated all infections with penicillin decided that the antibiotic was worthless because it didn’t cure every bacterial infection known to man.

According to the National Institutes of Health (NIH):

“More than 200 different viruses are known to cause symptoms of the common cold. An estimated 30-35% of all adult colds are caused by rhinoviruses.”

Symptoms of the common cold can also be caused by coronaviruses. Yes, viruses in the same family as the coronavirus responsible for COVID-19. Respiratory syncytial virus (RSV) can also trigger cold symptoms. It is estimated that 20% to 30% of colds are caused by unknown viruses.

As far as we can tell, none of the vitamin C studies have tested subjects for viral strains. Without determining the virus involved, it is hard to say unequivocally that vitamin C is worthless against the common cold.

Studies That Show Vitamin C Is Helpful Against Colds:

Ascorbic acid is important for the white blood cells of the immune system. Among other things, it protects them from oxidation damage and improves their ability to kill microbes. That finding suggests that vitamin C might be beneficial against a range of upper respiratory tract infections.

The reviewers of Vitamin C to help combat COVID-19 noted:

“…in five trials involving a total of 598 marathon runners, skiers and soldiers on subarctic exercises vitamin C reduced the incidence of colds by 52% (p < 0.0001). Based on these findings, vitamin C appears to influence resistance to viral infections in special conditions, such as during brief periods of severe physical exercise.”

There are other studies suggesting that regular intake of extra ascorbic acid can reduce the number of colds people get.

The reviewers conclude:

“In summary, cold symptoms have been shown to be less severe and resolve more quickly with oral vitamin C with a dose-dependent effect.”

Could Vitamin C Also Help Combat COVID-19?

You may be wondering whether extra vitamin C can help combat COVID-19.

According to the recent review in the journal Nutrients:

“There are currently 45 trials registered on Clinicaltrials.gov investigating vitamin C with or without other treatments for COVID-19.”

The authors also note that:

“Interestingly, many of the risk factors for COVID-19 overlap with those for vitamin C deficiency. Certain sub-groups (male, African American, older, those suffering with co-morbidities of diabetes, hypertension, COPD), all at higher risk of severe COVID-19, have also been shown to have lower serum vitamin C levels.”

There is reason to believe that this low-cost, low-risk essential nutrient can help reduce viral load and improve infection outcomes. Its antioxidant, antiviral, anti-inflammatory and anti-clotting activity offer wide ranging benefits against respiratory infections.

An updated review of 12 trials offers continuing support for this idea (Life, Nov. 1, 2021). We note, however, that some of the authors declared a conflict of interest. That doesn’t invalidate their analysis, but we will continue searching for further evidence.

The doses being tested range from two to eight grams per day. Is that safe?

Are Doses of Vitamin C to Help Combat COVID-19 Dangerous?

So far, investigators have not found serious side effects up to 3 or 4 grams/day. Here are a few red flags, though. People with blood disorders like hemochromatosis or thalassemia should avoid high-dose vitamin C. Those with glucose-6-phosphate deficiency should not exceed 6 grams/day. People at risk for kidney stones should probably avoid large doses, though this concern remains controversial.

Some consumers report that they experience loose bowels or diarrhea at doses above 3 grams/day. This is probably fairly common and may be a limiting factor for many people.

The authors of the recent review in Nutrients offer this overview:

“Vitamin C’s potential benefits, low cost, safety profile and multiple disease-modifying actions, including antioxidant, anti-inflammatory and immunomodulating effects, make it an attractive therapeutic candidate in reducing viral load with oral supplementation in the range of 2–8 g/day to help attenuate the conversion to the critical phase of COVID-19. Likewise, vitamin C has potential benefits in treating acute respiratory infections and mitigating inflammation in critical COVID-19 patients with intravenous vitamin C infusion in the range of 6–24 g/day, for correcting disease-induced deficiency, reducing inflammation, enhancing interferon production and supporting the anti-inflammatory actions of glucocorticosteroids, especially given the high level of fatality for patients with severe COVID-19.”

They conclude:

“People in high-risk groups for COVID-19 mortality, and at risk of vitamin C deficiency, should be encouraged to supplement with vitamin C daily to ensure vitamin C adequacy at all times, and to increase the dose when virally infected to up to 6–8 g/day.”

Of course such high doses should only be contemplated under careful medical supervision. Health professionals who are interested in the science behind using vitamin C to help combat COVID-19 can access the full text of the Nutrients article (“Vitamin C—An Adjunctive Therapy for COVID-19”) and the credentials of the authors at this link.

Do not imagine for a moment that taking vitamin C or any other nutrient is a substitute for vaccination. The only way we can get a handle on this pandemic is through highly effective vaccines that can prevent the spread of SARS-CoV-2. Unfortunately, variants that can escape immune protection may be moving us toward learning to live with COVID.

What Do You Think About Vitamin C to Combat COVID-19?

Do you take vitamin C? How much? Please share your thoughts in the comment section below. If you think this article is of use, please consider sharing it with friends and family by scrolling to the top of the page and sending it via email, Facebook or Twitter.

If you are not big on taking pills, you might like to know how to get ascorbic acid from food. Here is a recent article about food sources of vitamin C.

If you would like to learn more about vitamin C and dozens of other nutrients, we cannot think of a better book than Dr. Low Dog’s: Fortify Your Life: Your Guide to Vitamins, Minerals and More. Look for it in your local library.

And if you find our work helpful, please consider supporting our efforts by reading our content without ads at this link:

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About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.”.
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  • Markwell NW, "Vitamin C in the prevention of colds." Medical Journal of Australia, Dec. 27, 1947. DOI: 10.5694/j.1326-5377.1947.tb74386.x
  • Hemilä H et al, "Vitamin C May Increase the Recovery Rate of Outpatient Cases of SARS-CoV-2 Infection by 70%: Reanalysis of the COVID A to Z Randomized Clinical Trial."
  • Holford, P., et al, "Vitamin C—An Adjunctive Therapy for Respiratory Infection, Sepsis and COVID-19," Nutrients, Dec. 7, 2020, https://doi.org/10.3390/nu12123760
  • Holford P et al, "Vitamin C intervention for critical COVID-19: A pragmatic review of the current level of evidence." Life, Nov. 1, 2021. DOI: 10.3390/life11111166
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