Vitamin C and COVID-19: Researchers call for status testing and intravenous / oral supplementation

By Guan Yu Lim

- Last updated on GMT

Researchers call for testing of vitamin C status and its supplementation in Covid-19 patients  ©Getty Images
Researchers call for testing of vitamin C status and its supplementation in Covid-19 patients ©Getty Images

Related tags Vitamin c COVID-19

The high frequency of vitamin C deficiency in people with respiratory infections has led researchers to call for levels to be tested on Covid-19 patients, followed by either intravenous or oral supplementation.

This is according to a yet-to-be published review, where researchers from the UK, New Zealand and US said it was common to see serum vitamin C deficiency (≤11 μmol/l) in hospitalized COVID-19 patients.

In one example, a study in New Zealand found that patients with pneumonia had lower vitamin C status compared with healthy controls, and the patients in ICU were more severely deficient.

A Barcelona study found 17 of 18 COVID-19 patients in ICU had vitamin C deficiency, while in Colorado, all COVID-19 patients in ICU had low levels of vitamin C, and non-survivors had much lower levels, half with overt deficiency levels as found in scurvy.

Researchers said serum vitamin C levels in humans decline rapidly under conditions of physiological stress such as infections, and as some countries are battling a second wave of Covid-19 infections, they said vitamin C may be a potential adjunctive therapy with its good safety profile and low cost.

Given the favourable safety profile and low cost of vitamin C, and frequency of vitamin C deficiency in respiratory infections, it may be worthwhile testing patients vitamin C status and treating accordingly with intravenous use within ICUs and orally with doses between 2 and 8g/day in hospitalised and infected persons​,” they wrote.

Vitamin C has antioxidant, anti-inflammatory and immunomodulating effects, and evidence to date indicate that oral vitamin C (2-8g/d) may reduce incidence and duration of respiratory infections and intravenous vitamin C (2-24g/d) has been shown to reduce mortality, ICU and hospital stays, and time on mechanical ventilation in severe respiratory infections.

The review is currently awaiting peer review before publication in the Nutrients​ journal, under the Special issue ‘Vitamins C and D: global and population health perspectives’.

Measuring vitamin C levels

Accessing vitamin C levels can help clinicians decide the next course of treatment whether orally or intravenously.

In one RCT in China, vitamin c was given intravenously (24g/day) to covid-19 patients on ventilators. Mortality was reduced by 68% than in the most critically ill compared to placebo.

First author and founder of Institute for Optimum Nutrition, Patrick Holford explained that intravenous was a more effective delivery system, especially for people in more critical conditions such as using ventilators.

There are similar RCT trials in progress in Italy and Canada.

Another author, Dr Anitra C. Carr, who is also associate professor at the University of Otago, said “When people get severe respiratory infections, their requirement and utilisation of vitamin C goes up significantly which is why they usually need intravenous infusions. Large doses of oral vitamin C are not taken up by the body to the same extent as comparable intravenous vitamin C doses​.”

According to her, there are currently trials underway at the Cleveland Clinic (US) assessing oral vitamin C supplementation (8g/d) in Covid-19 patients.

Holford added: “The single biggest life-saving impact that we can make in the short-term is to take vitamin C, in high doses, for those in critical infection. I hope ICUs will start to use vitamin C as standard practice, as China is already​.”

In terms of safety, intravenous vitamin C can be administered up to 6g without toxicity. For oral dosages, Carr said there are no upper known toxicity level for vitamin C.

The body has regulated uptake of oral vitamin C by specialised vitamin C transporters in the small intestine, this limits the amount of oral vitamin C that can be taken up at any one time. Also because it is water soluble any excess that the body doesn’t need is rapidly cleared by the kidneys. Some people can get gastrointestinal upsets with oral doses >3-4 g/d but (they are) not common​.”

Vitamin C is safe and non-toxic, except in people with renal disease or failure as their kidneys can’t clear high plasma doses of vitamin C unless the individual is on dialysis​.”

It is also important to note potential interactions when supplementing with vitamin C, whether orally or intravenously.

Patients who are low in vitamin C are often low in other micronutrients so should be assessed for deficiencies​,” Carr said.

According to her and Holford, vitamin C can be administered alone or with other micronutrients such as vitamin E or zinc. However, iron or copper may result in a loss in vitamin C in liquid format.


Carr and her team are currently assessing vitamin C status and administering supplements to assess its effect in patients with pneumonia and sepsis.

For Holford, he is also testing vitamin C levels in blood and urine to ascertain levels of those critically ill on arrival and after vitamin c treatment.

My current project is to get vitamin C levels tested with a urine test in care homes. In the UK, an estimated 480,000 people over age 65 have overt vitamin c deficiency below 11µmol/l. With 44% of deaths being in care homes, these people in a pre-scurvy state are unlikely to survive a viral attack. So vitamin C needs go up with age​.”

Researchers advised high-risk groups and those at risk of vitamin C deficiency to take vitamin C daily and increase dosage to 6 to 8g/day when infected.




 “Vitamin C—An Adjunctive Therapy for Respiratory Infection, Sepsis and COVID-19”

Authors: Patrick Holford, Anitra C. Carr, et al​.

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