Vitamin C is best known for its antioxidant properties, being able to protect the body’s cells and tissues from oxidative damage and dysfunction (read antiaging). However, the vitamin also has numerous other important functions within the body, many of which are known to support healthy immune function.

Vitamin C benefits

• Plays a potential role in preventing, shortening, and alleviating diverse infections and pneumonia by facilitating the normal release of white blood cells
• Reduces the severity and duration of a cold
• Facilitates the absorption of iron (especially important in women).
• Helps your body stimulate collagen, a protein that forms connective tissue, blood vessels, cartilage, muscle and collagen in bones. 
• Supports healthy eyesight (especially in the elderly)
• It helps to maintain healthy cardiovascular function.

How much Vitamin C should you take daily?

Vitamin C is an essential water-soluble nutrient that cannot be synthesised or stored by humans, so we must consume it on a regular basis in order to maintain appropriate levels in the body.

The recommended dietary intake (RDI) in Australia is fairly low at 30-40mg for adults, and around 90mg in America. Pregnant and lactating women as well as smokers need higher doses of vitamin C.

These are considered the minimum amounts to prevent severe illnesses such as scurvy, and a much higher dose is needed to have a real effect on any infections.

A meta-analysis (mother of all research) of dose-dependency calculated that on average 1 g/day of Vitamin C shortened the duration of colds in adults on average by 6%-17% and 2 g/day Vitamin C shortened the duration of colds in adults by 21%-26%. Thus, higher doses were associated with greater effects. Nevertheless, we don’t have a clear cut answer to dosage and effectiveness. Vitamin C has been used in clinical settings for decades to prevent and reduce the effects of colds and as a result, we know that during a cold or the flu, Vitamin C levels can become depleted, and therefore a person’s requirement for Vitamin C increases with the severity of the infection, hence it makes sense to increase the Vitamin C intake during an infection (cold or flu)

A new clinical trial to investigate Vitamin C infusion for the treatment of severe COVID-19 infected pneumonia has begun in Wuhan, China. This is one of the first trials to test the effects of intravenous (IV) Vitamin C therapy in patients infected with this virus. In this trial, the investigators will treat patients with intravenous Vitamin C at a dose of 24 g/day for 7 days. They will assess requirements for mechanical ventilation and vasopressor drugs, organ failure scores, ICU length of stay and 28-day mortality.

Summary

At this point in time, no official amount of Vitamin C is being recommended, but from the studies available to us, we can see that the effectiveness of Vitamin C is dose-dependent and higher doses are needed during an infection.

It is safe to take 1-2000mg/day and this can be a sufficient preventative treatment. But as the cold starts to take hold and you feel a slight tickle in the throat, you can increase the daily intake to 3-6000mg/day. You can do this for the duration of the cold. Once you feel back to normal, reduce the intake to 1-2000mg/day during winter and possibly even less during summer, dependent on your average intake of fruit and vegetables.

Spread out the intake of Vitamin C over the course of the day, as the body can only absorb smaller amounts at a time, aim to take 500mg-1000mg at a time. Vitamin C can be taken with or without food, at any time of day.

Vitamin C is a water-soluble vitamin, which means that the risks associated with taking too much are generally low since the body can flush out excess amounts that it doesn’t need. However, the side effects of taking too much Vitamin C is an upset stomach and possibly diarrhea, if this happens scale back your intake to a tolerable dosage for your body.

References

Vitamin C for preventing and treating pneumonia. Cochrane Database Syst. Rev. 2013;8:CD005532. [Google Scholar]

Vitamin C for Preventing and Treating Pneumonia. [(accessed on 17 March 2017)]; Available online: http://www.mv.helsinki.fi/home/hemila/CP.

Preventing the common cold with a vitamin C supplement: A double-blind, placebo-controlled survey. Adv. Ther. 2002;19:151–159. doi: 10.1007/BF02850271. [PubMed]

Factors affecting the magnitude of the benefit. Med. Hypotheses. 1999;52:171–178. [PubMed]

The effect on winter illness of large doses of vitamin C. Can. Med. Assoc. J. 1974;111:31–36. [PMC free article] [PubMed]