Vitamin C has long been touted as an immunity booster, with claims ranging from it being useful for everything from the common cold through to far more serious issues. The research around Vitamin C is generally positive, although some of the health claims are definitely over blown. That’s not to say that you shouldn’t make sure to get enough of it, and not having enough will of course have negative effects on immunity.
It's also important to note that we rely solely on vitamin C from dietary sources and it’s essential for the immune system, but also everything from bodily functions through to healthy skin.
Vitamin C and The Immune System
Vitamin C is involved in the production of a lot of our immune cells, most notably our white blood cells. As many people know white blood cells are responsible for fighting off infections.  On top of that it’s also important for the production of antibodies.  As a result, we know for sure that getting the RDI is essential for a healthy immune system. The question is, does taking more vitamin C mean more immunity?
The Studies on Vitamin C and Immunity
First up we’ll start with the more negative studies, as of course we know that we do need vitamin C in general, we’re going to look at vitamin C beyond the recommend minimum or it’s effect on specific conditions.
Vitamin C and the Common Cold
For example, vitamin C and the common cold. As we mentioned in the intro, a lot of people claim that vitamin c can help fight off the common cold. And this is something of a misconception. Supplementing extra vitamin C was shown to improve immune response in blood samples, but it did nothing to shorten the length of or reduce the symptoms of the virus.  So technically, yes it does improve your bodies ability to fight it off, but that didn’t actually translate to any tangible difference.
However, there have been other studies that have shown when fighting off the cold, and other respritory issues vitamin C can improve the recovery time especially when combined with zinc and vitamin D. 
And on top of that getting enough vitamin C has been associated with a reduced rate of and improved outcome of pneumonia, malaria, and diarrhea infections, particularly in children in developing countries. Although several of these studies are a case of getting enough vitamin C, rather than over supplementing a pre existing diet, others did show an improved outcome.
Vitamin C as an Anti Oxidant
Free radicals do cause damage to the body, and vitamin C has also been shown to help improve the bodies defenses in this regard improving it’s anti oxidant response. Certain conditions that are made worse by oxidative stress could benefit from vitamin C although the research is still early.  This includes several neurological conditions, as well as things like diabetes and arthritis. This is particularly useful as it’s shown some promise with reducing inflammation too.
How Much Vitamin C Do I Need?
The Recommended Dietary Intake (RDI) for vitamin C varies depending on factors such as age, sex, and life stage. For adult men and women, the RDI is generally around 75-90 milligrams per day.  There are some times when this could be different, for example this can go up a little during pregnancy for example. It is also possible to take too much vitamin C although it's quite difficult and is most likely to only cause a stomach upset in most cases.
So, is it Worth Taking Vitamin C Supplements When You're Sick?
Seeing as this is quite possibly why many people are reading this article. It's important to note that whilst vitamin C may not be a miraculous cure for the common cold, it undoubtedly plays a vital role in supporting immune function and overall health. If you think you're not getting enough, then yes, you probably would benefit from a vitamin C supplement seeing as vitamin C is essential to maintain a robust immune system and protect against various infections and diseases.
1 - Davood, Jafari., Abdolreza, Esmaeilzadeh., Marziyeh, Mohammadi-Kordkhayli., Nima, Rezaei. (2019). Vitamin C and the Immune System. doi: 10.1007/978-3-030-16073-9_5
2 - Anitra, C., Carr., Silvia, Maggini. (2017). Vitamin C and Immune Function. Nutrients, doi: 10.3390/NU9111211
3 - Alexander, Ströhle., Andreas, Hahn. (2009). Vitamin C and immune function. Medizinische Monatsschrift für Pharmazeuten,
4 - Stephen, Beveridge., Eva, S., Wintergerst., Silvia, Maggini., D., Hornig. (2008). Immune-enhancing role of vitamin C and zinc and effect on clinical conditions. doi: 10.1017/S0029665108006927
4 - Voja, Pavlovic., M., Sarac. (2011). A short overview of vitamin C and selected cells of the immune system. Central European Journal of Medicine, doi: 10.2478/S11536-010-0066-X
6 - https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/