Vitamin C for Colds, Flu and COVID-19

Oranges Contain Significant Vitamin C

Vitamin C has long been considered a support for the immune system. As such, you often hear recommendations for taking vitamin C to help prevent and treat colds and flu or even COVID-19. Yet over the years, the research on vitamin C has been somewhat mixed. With the cold and flu season upon us, it’s worth seeing what the latest research suggests.

The Latest Meta-Analysis

When it comes to colds and flu, there are three main parameters to consider: prevention, the severity and the duration of illness. The most recent meta-analysis combined the latest research and found that taking vitamin C may help prevent colds and flu, but the effect was small and didn’t reach full clinical significance (Keya 2022). 

As for reducing the severity of colds and flu, vitamin C doesn’t appear to have a strong effect. However, vitamin C does appear to significantly shorten the duration of being sick. Therefore, according to the latest data, vitamin C has modest but significant effects. It may slightly decrease your risk of becoming sick if you take it consistently and it should help you recover more quickly. 

If vitamin C is all you have, I wouldn’t hesitate to use it. However, there are other natural options that I’ve covered previously that also appear to reduce the incidence, severity and duration of colds and flu, including:

Vitamin C and Covid-19

Oral Vitamin C for COVID-19

Data on vitamin C and COVID-19 is still controversial. An early trial found that patients with COVID-19 had almost five-fold lower levels of vitamin C in the blood. These low levels were easily restored with high-dose supplementation of 100 mg/kg of vitamin C per day (Xing 2021). A study using high dose oral supplementation for COVID-19 found that vitamin C shortened the time to a 50% reduction in symptoms by almost one day, but the results failed to reach clinical significance (Thomas 2021). A study on 1000 mg per day in COVID-19 patients didn’t find mortality benefits but the vitamin reduced blood clotting events by more than half (Sulaiman 2021). 

In more severe cases, a separate trial using just 500 mg of vitamin C daily in critically ill COVID-19 patients did find survival benefits. Patients on vitamin C survived an average of eight days as compared to only four days without (Majidi 2021). However, a study on mild to moderate COVID-19 patients found that 1000 mg of oral vitamin C had no effect on the progression of COVID-19 symptoms (Fogleman 2022).

In total, an overall meta-analysis of studies found that oral vitamin C supplementation reduced in-hospital mortality from 51.8% to 39.3% (Olczak-Pruc 2022). While the data is still early, it is suggestive that vitamin C is helpful in treating COVID-19. 

Intravenous Vitamin C for COVID-19

Oranges Are a Source of Vitamin C

Since the maximum dose of oral vitamin C is limited due to bowel tolerance, intravenous vitamin C can be used to increase blood levels higher than what is possible with oral supplementation. High-dose vitamin C, administered Intravenously, has been explored as a treatment for COVID-19. 

In the most recent meta-analysis of vitamin C for COVID-19, intravenous vitamin C reduced mortality significantly. Patients on intravenous vitamin C had a mortality rate of 13% as compared to 18.9% without (Olczak-Pruc 2022). Again, the data suggests benefits with vitamin C for treating COVID-19.


Vitamin C appears to have value for treating colds, flu and COVID-19. For colds and flu, the benefits are modest, possibly helping with prevention and shortening the duration of illness. For COVID-19, there appears to be a true survival benefit for both oral and intravenous supplementation. Considering the safety of vitamin C, it would appear to make sense to consider including it as part of a standard protocol for improving COVID-19 outcomes. 

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