You look like an intelligent person with some common hearsay opinions contaminating your information base. Because of the structure of how these have been implanted over generations in the medical fields, most PhDs and MDs don't even begin to recognize their problem on accurate megavitamin information. Or where to start with the original scientific and medical papers. ...Very large doses of some vitamins can actually make you very sick or significantly increase your cancer risk
Clearly not dealing with preferred forms and regimens of nutrients if that happens. There also is some skill, supervision or basic education missing if that happens.
You might look at the old injectable vitamin C papers and the recent failures on vitamin D RDA setting (e.g. 200 iu D2 in 1992 vs 2000-5000 iu in 2017 for saavy arctic living) as a starting point.
One clue: When someone speaks to me about "antioxidants" or an indiscriminate vitamin letter rather than the actual molecular entity, their credibility takes a big hit. The particular molecule(s), mixture or regimen can make a huge difference in megadose therapeutic situations.