Can taking extra vitamin c every day help prevent you from catching the coronavirus or the flu? if so, how much vitamin c is recommended?

Vitamin C: Sorry to maybe disappoint you, but there is no evidence that vitamin C helps prevent colds and almost certainly would not prevent influenza or coronavirus infection.

Vitamin C: While getting enough vitamin C in your diet is highly recommended, it has no special ability to prevent coronavirus or flu virus. Best preventative measures for these are frequent handwashing and avoiding people with sneezing/coughing/cold symptoms and fevers.

No: Not recommended, although vitamin C 100-200 mg per day orally for patients age 4 years and older may decrease duration of one's colds, but doesn't prevent colds. "May" means there is uncertainty. Large vitamin C intake causes gastrointestinal side effects. While unclear if there is a benefit, some adults take large 1-2 gram per day doses of vitamin C during colds to try to decrease cold symptoms.

COVID 19: I am not aware of literature that shows that Vitamin C will prevent transmisison of COVID 19 or influenza.