Vitamin C: Coronavirus, Benefits and Side Effects

Vitamin C has been a subject of controversy for many years. It may appear to be as simple as ABC, but is not. What's so confusing about Vitamin C? Let's dive into some facts and evidence.

Vitamin C - The Basics

Vitamin C, also known as L-ascorbic acid, is a water-soluble vitamin that is naturally present in some foods, added to others, and available as a dietary supplement. Humans, unlike most animals, are unable to synthesise vitamin C endogenously, so it is an essential dietary component.



The recommended daily intake for vitamin C is 75 mg for women and 90 mg for men.

While it’s commonly advised to get your vitamin C intake from foods, many people turn to supplements to meet their needs.

Can Vitamin C Protect You against COVID-19?

As of February 2021, more than 50 studies have been launched to investigate the benefits of vitamin C against COVID-19. There are many such studies underway and you can review the status of these trials on clinicaltrials.gov

A review, published December 7, 2020, in the journal Nutrients, recommended the use of vitamin C as an additional therapy for respiratory infections, sepsis and COVID-19.

In December 16, 2020, Rob Verkerk, Ph.D., founder and scientific director of the Alliance for Natural Health, announced the launch of an international vitamin C campaign in response to the Nutrients review, which "puts all the arguments and science in one, neat place."

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 . Average plasma vitamin C levels are generally lower in men than women, even with comparative intakes of vitamin C, which has been attributed to their higher body weight . 

In the first RCT (Randomised Controlled Trial) to test the value of vitamin C in critically ill COVID-19 patients, 56 ventilated patients in Wuhan, China, were treated with a placebo (sterile water) or intravenous vitamin C at a dose of 24 g/day for 7 days. The trial was originally designed for 140 subjects and was thus underpowered, with only 54 patients due to a lack of new admissions. The authors concluded that HDIVC (high dose intravenous Vitamin C) might show a potential signal of benefit for critically ill patients with COVID-19.

The Frontline COVID-19 Critical Care Expert Group (FLCCC), a group of emergency medicine experts, have reported that, with the combined use of 6 g/day intravenous vitamin C (1.5 g every 6 h), plus steroids and anticoagulants, mortality was 5% in two ICUs in the US (United Memorial Hospital in Houston, Texas, and Norfolk General Hospital in Norfolk, Virginia), the lowest mortality rates in their respective counties .

Word of Caution - The U.S. Recommended Dietary Allowance (RDA) for vitamin C is 75 to 120 milligrams per day. Taking large doses of vitamin C (ascorbic acid) on a regular basis lowers your level of copper, so if you are already deficient in copper and take high doses of vitamin C, you can compromise your immune system.

While generally considered safe even in high doses, way too much vitamin C — anything above 2,000 milligrams daily—can cause headaches, insomnia, gastric discomfort, diarrhea, heartburn, and other issues.

Temporarily taking megadoses of vitamin C supplements to combat a case of the cold or flu is likely not going to cause a problem. 

Many vitamin C supplements that are above the US RDA are sold in the market. It’s important to seek a physician’s advice if you intend to take high dose vitamin C on a long term basis. High doses of vitamin C (over 500 mg per day) over the long-term may increase the risk of cataracts. High-dose vitamin C can also reduce the effectiveness of certain medications and interfere with certain blood tests.

To be on the safe side, you may also request for your kidney functions to be monitored.

For long-term, daily use, your best bet is to eat a diet that is full of high quality organic vegetables and fruits that are minimally processed. Not only will you get vitamin C, but you will get all the other accessory nutrients and micronutrients that are needed to optimize it.

That said, there are also several reasons to consider taking supplemental vitamin C. Firstly, your body cannot make it. Secondly, most people do not get sufficient amounts from their diet and, thirdly, your body’s requirement for vitamin C can increase 10-fold whenever your immune system is challenged by an infection, disease or physical trauma.

But basically, vitamin C supplementation is a pretty low-risk intervention. It's easy for decision-makers and doctors to sit and do their online research and say, "Wait for more data." But if a loved one was in the ICU with sepsis or COVID-19, would you ask for vitamin C? After reviewing the literature, I'd be hard-pressed to dismiss it out of hand.

Related: Best Vitamin C Supplements


Sources of Vitamin C - Food

Fruits and vegetables are the best sources of vitamin C. Citrus fruits, tomatoes and tomato juice, and potatoes are major contributors of vitamin C to the American diet. Other good food sources include red and green peppers, kiwifruit, broccoli, strawberries, Brussels sprouts, and cantaloupe. Although vitamin C is not naturally present in grains, it is added to some fortified breakfast cereals. The vitamin C content of food may be reduced by prolonged storage and by cooking because ascorbic acid is water soluble and is destroyed by heat. Steaming or microwaving may lessen cooking losses. Fortunately, many of the best food sources of vitamin C, such as fruits and vegetables, are usually consumed raw. Consuming five varied servings of fruits and vegetables a day can provide more than 200 mg of vitamin C.

Sources of Vitamin C - Dietary supplements and Different Forms of Vitamin C

Supplements typically contain vitamin C in the form of ascorbic acid, which has equivalent bioavailability to that of naturally occurring ascorbic acid in foods, such as orange juice and broccoli. Other forms of vitamin C supplements include sodium ascorbate; calcium ascorbate; other mineral ascorbates; ascorbic acid with bioflavonoids; and combination products, such as Ester-C®, which contains calcium ascorbate, dehydroascorbate, calcium threonate, xylonate and lyxonate.

A few studies in humans have examined whether bioavailability differs among the various forms of vitamin C. In one study, Ester-C® and ascorbic acid produced the same vitamin C plasma concentrations, but Ester-C® produced significantly higher vitamin C concentrations in leukocytes 24 hours after ingestion. Another study found no differences in plasma vitamin C levels or urinary excretion of vitamin C among three different vitamin C sources: ascorbic acid, Ester-C®, and ascorbic acid with bioflavonoids.

Liposomal Vitamin C

Liposomal vitamins don’t use capsules or tablets or powders to deliver nutrients. Instead, the vitamins are encapsulated in pockets of fat cells called liposomes (hence the name). Apparently this is the most effective way of ensuring the vitamins in the supplement actually get absorbed into your body.


Vitamin C To Boost Your Immune System

One of the main reasons people take vitamin C supplements is to boost their immunity, as vitamin C is involved in many parts of the immune system. 

First, vitamin C helps encourage the production of white blood cells known as lymphocytes and phagocytes, which help protect the body against infection (PubMed).

Second, vitamin C helps these white blood cells function more effectively while protecting them from damage by potentially harmful molecules, such as free radicals.

Third, vitamin C is an essential part of the skin’s defense system. It’s actively transported to the skin, where it can act as an antioxidant and help strengthen the skin’s barriers (ScienceDirect).

Studies have also shown that taking vitamin C may shorten wound healing time (PubMedPubMed).

What’s more, low vitamin C levels have been linked to poor health outcomes.

Vitamin C other Benefits

A review of 28 studies (Diabetes Care. 2021 Feb) in 1,574 people with type 2 diabetes mellitus, demonstrated that vitamin C supplementation may improve blood sugar control and blood pressure in people with type 2 diabetes.

People who have pneumonia tend to have lower vitamin C levels, and vitamin C supplements have been shown to shorten the recovery time (PubMedPubMed).

A large review of 29 studies in 11,306 people demonstrated that regularly supplementing with vitamin C at an average dose of 1–2 grams per day reduced the duration of colds by 8% in adults and 14% in children (PubMed).

Interestingly, the review also demonstrated that regularly taking vitamin C supplements reduced common cold occurrence in individuals under high physical stress, including marathon runners and soldiers, by up to 50% (PubMedPubMed).

Additionally, high dose intravenous vitamin C treatment has been shown to significantly improve symptoms in people with severe infections, including sepsis and acute respiratory distress syndrome (ARDS) resulting from viral infections (PubMedPubMed).

Side Effects of too much Vitamin C

Since vitamin C is water-soluble and your body excretes excess amounts of it within a few hours after you consume it, it’s quite difficult to consume too much.

The U.S. Recommended Dietary Allowance (RDA) for vitamin C is 75 to 120 milligrams per day. Taking large doses of vitamin C (ascorbic acid) on a regular basis lowers your level of copper, so if you are already deficient in copper and take high doses of vitamin C, you can compromise your immune system. It is suggested that dietary ascorbic acid reduces tissue copper concentrations primarily by interfering with intestinal copper absorption. 

In fact, it is nearly impossible for you to get too much vitamin C from your diet alone. In healthy people, any extra vitamin C consumed above the recommended daily amount simply gets flushed out of the body (PubMed). To put it in perspective, you would need to consume 29 oranges or 13 bell peppers before your intake reached the tolerable upper limit (USDA), which is 2 grams/day.

However, the risks of vitamin C overdose are higher when people take supplements, and it is possible to consume too much of the vitamin in some circumstances. For example, those with conditions that increase the risk of iron overload or are prone to kidney stones should be cautious with their vitamin C intake (PubMedPubMed).

For those with beta-thalassemia major and sickle cell anemia who suffer from iron overload due to regular blood transfusions or excessive destruction of red blood cells need specialized medical treatment with iron chelators and should also control their intake of iron (PubMed).

All the adverse effects of vitamin C, including digestive distress and kidney stones, appear to occur when people take it in mega doses greater than 2,000 mg (PubMed).

In summary, individuals with existing renal disease, Glucose-6-Phosphate Dehydrogenase Deficiency (G6PD), kidney stones, or Hemochromatosis should avoid high dose Vitamin C.

Temporarily taking megadoses of vitamin C supplements to combat a case of the cold or flu is likely not going to cause a problem. 

Many vitamin C supplements that are above the US RDA are sold in the market. It’s important to seek a physician’s advice if you intend to take high dose vitamin C on a long term basis. High doses of vitamin C (over 500 mg per day) over the long-term may increase the risk of cataracts. High-dose vitamin C can also reduce the effectiveness of certain medications and interfere with certain blood tests.

To be on the safe side, talk to your doctor and you may also request for your kidney functions to be monitored as well.

For long-term, daily use, your best bet is to eat a diet that is full of high quality organic vegetables and fruits that are minimally processed. Not only will you get vitamin C, but you will get all the other accessory nutrients and micronutrients that are needed to optimize it.

Choosing a Vitamin C supplement

If you do choose to take a vitamin C supplement, it’s important to choose one that’s high quality and to take the correct dose.

While supplements are regulated by the Food and Drug Administration (FDA), they aren’t held to the same safety standards as pharmaceuticals. Thus, it’s important to purchase supplements from reputable companies.

Some third-party organizations, such as NSF International, ConsumerLab, and United States Pharmacopeia (USP), test supplements for purity and label accuracy. You may want to choose a vitamin C supplement that has been tested by one of these companies.

Additionally, the Upper Limit (UL) for supplemental vitamin C — the amount most people can consume daily without negative effects — is 2,000 mg (nih.gov).

Most vitamin C supplements provide a daily dose of anywhere from 250–1,000 mg, so it can be easy to exceed the UL if you’re not careful. Be sure to read the packaging and take only the recommended dose to avoid complications.

Vitamin C may also interfere with chemotherapy, radiation treatments, or cholesterol lowering drugs (nih.gov).

That said, when used in clinical settings treating critically ill patients, very high dose vitamin C treatments are safe and not associated with significant side effects (Critical Care).

If you have any concerns about vitamin C supplements, you should consult your healthcare provider before adding it to your routine.

References: 

  1. https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/
  2. https://www.healthline.com/nutrition/vitamin-c-coronavirus

Editor's Note: The subject on Vitamin C supplement has been controversial. Although we have tried to summarise and tried to provide important essential information on this topic, it's also likely that we have missed out some important information as well; or it's still confusing.

Allow us to provide a few practical tips:

Let's begin with the non-controversial part. Yes, we need Vitamin C and we should ideally get it from whole fruits and vegetables.

The controversial part is on Vitamin C 'supplement'. Should we supplement our diet with Vitamin C supplement? My answer is Yes, as most people do not take 5 servings of fruits and vegetables. Further, Vitamin C is easily destroyed by heat during cooking and our human bodies are not capable of producing and storing Vitamin C. That being said, I would not recommend taking high dose of Vitamin C as maintenance. Up to 500 mg/day should be reasonable.

As for high dose Vitamin C supplement, I would suggest that you discuss with your doctor. This is a more complicated subject as the indications for high dose Vitamin C are considered prescription dosage and is meant for 'treatment' and not 'maintenance'.

So should you just focus on Vitamin C alone or should you consider other supplements? Vitamin C alone might not be enough as an optimal strategy. A combination and a synergistic mix of supplements would be better. 

What if you have seen multiple doctors and they are giving you mixed recommendations? Our recommendation is to stick to a data driven principle and discuss the evidence out there with doctors who are open to be updated with data-driven science and evidence based medicine.

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