vitamin C in orange juice form is 1litre=0.5grams
anyone suggesting 5-8gram means someone has to drink 10-15 litres of orange juice
the human body only needs ~0.1g not 5g-8g
200ml or OJ (a cup/glass) is all you need. not 10-15 litres
telling people to have 5 litres of OJ or chew on 5 VitC suppliment tablets a day is foolish non-science
your body only uses what it needs and excretes the rest....
Unfortunately there are no good studies on oral Vitamin C. All we have are a bunch of very small underpowered studies. There is even less data on dosing. The doses given in these small studies typically ranged from 500mg to 3000mg daily with the lower end dosing being more much more common. Vitamin C is generally harmless but can cause GI upset at high doses.
Here are four small studies looking at Vitamin C in the setting of cold or flu 3 showed a benefit one did not. All were very small.
There is of course no data at all looking at vitamin C and coronavirus. That said am currently taking 1g a day because the potential downsides are so negligible.
https://pubmed.ncbi.nlm.nih.gov/10543583/https://pubmed.ncbi.nlm.nih.gov/16118650/https://www.ncbi.nlm.nih.gov/pmc/articles/PMC478963/https://pubmed.ncbi.nlm.nih.gov/11700812/