top of page

COVID-19: Prevention and Treatment, Vitamin C

Doctors working with COVID-19 patients in China observed many patients having better medical outcomes when they used vitamin C supplements. These observations were so consistent they initiated a clinical trial to test the effectiveness of high dose IV vitamin C as a stand-alone treatment. This phase II study began on February 11, 2020, is registered on, and expects to have results by September 30, 2020. Their registration listing references a body of literature showing vitamin C has positive treatment effects on a wide range of COVID-19 related symptoms. That said, there is as yet no direct evidence that vitamin C supplementation has prevention or treatment value for the virus causing COVID-19.

According to the US National Institutes of Health, Vitamin C is a powerful antioxidant that contributes to overall heath, is required for many physiological processes, and helps maintain organismic homeostasis. It is crucial to multiple areas of immune system functioning. Vitamin C has been found to effectively prevent and or treat multiple diseases, including some respiratory infections. Separate analyses document its safety at even high levels of supplementation. More information about dosages, delivery methods, and safety is presented below.

Supplementation of vitamin C has been found to reduce the risk of cold infections by half when the person experienced significant physical stress. Remember that psychological stress produces physical stress. Vitamin C has also been found to reduce symptom severity and the duration of colds and flus, and to reduce the risk of flu infection. The COVID-19 virus belongs to the same coronavirus family as cold and flu viruses, and produces similar symptoms once infected.

Dr. Hemilä of the University of Helsinki performed the most recent complete analysis of the available research evidence on Vitamin C. ln the abstract of her 2017 article “Vitamin C and Infections” she wrote:

“In the early literature, vitamin C deficiency was associated with pneumonia. After its identification, a number of studies investigated the effects of vitamin C on diverse infections. A total of 148 animal studies indicated that vitamin C may alleviate or prevent infections caused by bacteria, viruses, and protozoa. …Two controlled trials found a statistically significant dose–response, for the duration of common cold symptoms, with up to 6–8 g/day of vitamin C. Thus, the negative findings of some therapeutic common cold studies might be explained by the low doses of 3–4 g/day of vitamin C. Three controlled trials found that vitamin C prevented pneumonia. Two controlled trials found a treatment benefit of vitamin C for pneumonia patients.”

Her research has uncovered a strong dose response relationship, that is, the higher the vitamin C dose, the stronger the beneficial effects. When discussing the results of her analysis, Dr. Hemilä concludes that "given the consistent effect of vitamin C on the duration of colds, and its safety and low cost, it would be worthwhile for individual common cold patients to test whether therapeutic 8 g/day vitamin C is beneficial for them. Self-dosing of vitamin C must be started as soon as possible after the onset of common cold symptoms to be most effective."

Many people with severe COVID-19 symptoms experience respiratory distress requiring admission to a hospital’s intensive care unit (ICU) and mechanical ventilation. A meta-analysis of 6 studies found oral administration of 1-3 grams of vitamin C reduced length of stays in the ICU by 8.6%. The combined results from three studies show that vitamin C administration reduced the duration of mechanical ventilation by 18.2%.


The above information does not tell us whether supplementing vitamin C has any effect on COVID-19 infection risk or treatment. We do know from this information that vitamin C is inexpensive and carries very little risk of harm, even at higher dosing levels.

If you choose to supplement with vitamin C as a preventive, you might want to start with 2 grams a day administered orally, preferably using a buffered or liposomal form (see the Delivery Methods section below). That should be sufficient to strengthen your immune system. If you choose to use a higher dose of regular vitamin C, pay attention to when you begin to develop gastric distress or diarrhea then reduce the dose until those symptoms disappear.

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. You may want to keep a supply of liposomal vitamin C on hand to allow you to deliver this high of a dose without unwanted side effects.

Delivery Methods

The goal with most supplements is to have the nutrient delivered to all tissues throughout the body. This is accomplished primarily through the blood circulatory system. There are three ways of taking vitamin C: standard vitamin C orally, liposomal vitamin C orally, and liquid vitamin C intravenously. These three methods produce widely varying bioavailability of the vitamin, that is, how much of the vitamin taken in actually gets used by the body.

Standard vitamin C, orally:

This is the method most people use and are familiar with. The vitamin is ingested and the digestive system is responsible for absorbing the vitamin and carrying it to the bloodstream. But there are problems.

Many low-cost vitamin manufacturers pack the vitamin in pills using binders that are not easily dissolved by the digestive system, so some or most of the pill itself passes through undigested and gets evacuated. Higher quality vitamins dissolve more completely, making more of the vitamin available. Powdered vitamins tend to be best dissolved, but the products also tend to be loaded with sugar which is not something you want to increase your intake of.

The second issue is absorption. Vitamin C requires specialized cells in the small intestine to carry it through the intestinal walls and into the bloodstream. There are only so many of these cells. Once they’ve carried about 200 mg of C into the bloodstream, the amount they transport drops off rapidly so they start transporting only about 50% of the rest of what’s available. This percentage continues to drop as more vitamin C is ingested. This leads to increasingly diminished absorption with increased consumption.

Liposomal vitamin C, orally:

Liposomal vitamin C is manufactured with a layer of fat around the vitamin molecules, which essentially mimics the action of the specialized transport cells. This allows almost all of the ingested vitamin to move through the intestinal walls into the bloodstream no matter the amount ingested. Because absorption is no longer limited by the availability of the transport cells, there are no diminishing returns with increased consumption.

Liquid vitamin C, intravenously:

Intravenous administration bypasses the gastrointestinal (GI) tract and delivers vitamin C directly to the bloodstream. The upper limit dosing of 2 g/day mentioned below is based on the potential development of diarrhea due to vitamin C sitting in the GI tract and not being absorbed. There is no safety limit yet identified for IV administration. IV administration of vitamin C can only be performed by healthcare professionals, and several clinical trials using this treatment have been completed. The FDA has not approved high-dose vitamin C for treatment in cancer or other conditions.


The Food and Nutrition Board of the US Institute of Medicine set the current recommended intake and safety levels for vitamin C in the standards in the year 2000. Their report says “the evidence of adverse effects due to intakes of vitamin C supplements is at this time limited to osmotic diarrhea and gastrointestinal disturbances which are self-limiting.” They set the Tolerable Upper Intake Levels (ULs) for adults for vitamin C at 2,000 mg/day based on the dose likely to not elicit osmotic diarrhea in the average person.

Both diarrhea and gastric distress occur only with oral delivery of standard vitamin C. Diarrhea is caused by unabsorbed vitamin C attracting water to it in the intestines. This can be countered by taking a form of vitamin C that is absorbed more fully. Gastric distress, which can be felt as stomach pain, cramping, or nausea, is primarily caused by the high acidity of the vitamin (ascorbic acid). This can be countered by lowering the dose or by using a product that is buffered. Buffering means using a second compound to reduce the acidity of the vitamin C, usually in the form of calcium ascorbate or rose hips.

The Food and Nutrition board also recommended that men with any form of kidney disease not take more than 2,000 mg/day to avoid risk of developing kidney stones. This risk has not been found in women.

Pregnant women should not take more than 2,000 mg/day to avoid even the remote possibility of fetal harm. Such harms have not been found in any clinical study, but there have been anecdotal and isolated reports of harm.

Five years after the Institute of Medicine report above was published, a complete review of vitamin C safety studies and clinical trials found “dietary supplements of vitamins E and C are safe for the general population. Many clinical trials with these vitamins have involved subjects with various diseases, and no consistent pattern of adverse effects has occurred at any intake.”

Featured News
Recent Posts