No, vitamin C does not prevent the flu, nor does it even reduce its direct symptoms. However, everything indicates that this antioxidant does reduce the sequelae of inflammation derived from virus infection.
Home remedies for the flu are very diverse. Those of us who comb gray hair remember warm milk with honey or an egg yolk, even with some punch. But there is one that survives the passage of time and we can consider the best known and accepted: a good dose of vitamin C.
Is there a scientifically based reason to turn to vitamin C as a remedy against the flu? No, there is not for direct symptoms. Although yes for the possible sequels.
Although some studies have shown some ability of vitamin C to prevent some of the symptoms of the flu, the reality is that they present design problems. In fact, when a comprehensive study has been conducted looking at multiple attempts to determine if vitamin C treatment actually improves flu symptoms, the results have been either none or very modest and only with excessively high doses such as 1 gram daily. Far from what a glass of orange juice or a handful of strawberries contains, for example.
In fact, the latest studies on clinical studies – what we know in the scientific world as meta-analyses and systematic reviews – emphatically conclude that only vaccines produce preventive effects, while the effect of vitamin C is negligible or null in terms of symptoms straight from the flu.
Vitamin C: a great soluble antioxidant
Our body has molecular antioxidants that can be classified as water-soluble or water-soluble, such as vitamin C and glutathione, and fat-soluble or fat-soluble, such as coenzyme Q10 and vitamin E.
These antioxidants fulfill an essential function: they reduce the levels of free radicals from oxygen or nitrogen metabolism, such as superoxide or hydrogen peroxide, and other more reactive ones that strongly attack DNA, producing mutations, such as hydroxyl radical or peroxynitrite.
Water soluble antioxidants reduce oxidative damage by scavenging some of these free radicals. On the other hand, those soluble in fats block the oxidation of membranes, preventing multiple effects on cell activity. They also prevent cell death by a mechanism known as ferroptosis.
Antioxidants need enzymes to recycle them
For an antioxidant to be useful in our cells, it needs enzymes that continually recycle it. This creates a cycle in which the active version of the antioxidant molecule is consumed over and over again by reacting against radicals, but is recycled by antioxidant enzymes in cells so that it can react again.
This cycle is known as the oxidation-reduction cycle, since the antioxidant oxidizes and reduces the free radical, eliminating it. Therefore, in order for antioxidant molecules to fulfill their function, they must have antioxidant enzymes in sufficient quantity and capacity to be endlessly recycled.
Therefore, gorging ourselves on antioxidant supplements does not make much sense if what is not working in our body are the enzymes that keep these molecules active. And when the body is out of balance, as occurs in chronic metabolic diseases or aging, these antioxidant enzymes function relatively poorly or are almost absent.
Vitamin C could prevent long-term damage
We all know the symptoms of the flu: cough, runny nose, malaise, fever, and joint pain. Influenza viruses invade cells and trigger an immune system response that produces a general inflammatory effect that causes fever and characteristic joint pain.
In all this inflammatory phenomenon, free oxygen radicals are generated that add even more damage to the direct damage produced by the virus itself. Increased production of free radicals during the flu generates a series of damage to cells and tissues that can aggravate degenerative processes and accelerate the accumulation of cellular waste.
These long-term damages could be behind the consequences that have been associated with influenza epidemics and that end up causing premature deaths even years later.
For this reason, the use of antioxidants could be considered a preventive therapy for the oxidative damage generated by the general inflammation produced by the viral infection of both influenza and covid-19.
We could, therefore, consider that vitamin C in the treatment of influenza is very useful to prevent oxidative damage that occurs due to the inflammatory effects derived from virus infection. In a well-fed person it would not be very necessary. However, in cases of deficiency or in the elderly, prevention is better than cure.
After all, a moderate excess of vitamin C prevents oxidative damage without side effects. And since it clears up quickly, any help is welcome even if it doesn't reduce symptoms much.
This article has been published in 'The conversation'.