Vitamin C If you are not ill, I suggest taking 3-5,000 mg/day of vitamin C. At the first sign of an illness, I would suggest taking 1,000 mg/hour until diarrhea develops, then back off for a time period.
Vitamin A For vitamin A, I suggest using 5,000 Units/day if you are not sick and 100,000 Units/day for four days at the first sign of an illness. Pregnant women cannot take these doses. (Note: Take vitamin A, not beta carotene.)
Vitamin D Also, vitamin D is very important for fighting infections. I suggest, at the onset of an illness, taking 50,000 IU of vitamin D3/day for four days.