Very weak evidence that systematic review papers are the way to go to figure this out. Chris van Tulleken on BBC News says:
“Looking at any one individual study won't be very revealing to answer the question of whether vitamin supplementation is good for you. They're densely scientific and the conflicts of interest can be very hard to spot.
“For the answer you have to turn to what are called “systematic review papers”. This is where independent scientists gather up all the available data and re-analyse it to answer big questions.”
Strong evidence against supplementing: “We found no evidence to support antioxidant supplements for primary or secondary prevention [of diseases of any kind]. Beta-carotene and vitamin E seem to increase mortality, and so may higher doses of vitamin A. Antioxidant supplements need to be considered as medicinal products and should undergo sufficient evaluation before marketing.”
Supposedly from one of:
- Bjelakovic G, Nikolova D, Simonetti RG, Gluud C. Antioxidant supplements for preventing gastro-intestinal cancers, , 2004
- Bjelakovic G, Nikolova D, Gluud C, Antioxidant supplements to prevent mortality, The Journal of the American Medical Association, 2013
- Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG, Gluud C, Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases, Cochrane Database of Systematic Reviews, 2012