Scientists have long known that vitamins C and E can be antioxidants in low concentrations but tissue- and DNA-destructive pro-oxidants in high concentrations. A recent clinical trial conducted at the Bertram Diabetes Research Unit and the Institute for Food Research in Norwich in England finds that there really is such a thing as getting to much alpha-tocopherol.
Scientists gave diabetics a daily dose of either a placebo or 1200 IU (800 mg) of alpha-tocopherol, one of the eight chemicals known as "vitamin E," every day for 29 days. At first there were no differences between the diabetic volunteers who got the placebo and those who got vitamin E.
By day 29, however, evidence of pro-oxidant effects began showing up in the diabetics who got the high-dose vitamin E. By day 29, from 6 to 20 per cent of the white blood cells (particularly the kind that get "stuck" in oxidized cholesterol) in the vitamin E treatment group had DNA damage.
This finding suggests that if you are a diabetic who takes just alpha-tocopherol, that is, no other form of vitamin E, and no other antioxidants, you are taking a damaging amount of vitamin E.
It's easy to correct the problem, of course. Take less alpha-tocopherol, and if you have a medically determined indication for high-dose vitamin E, take a supplement that contains at least gamma-tocopherol and preferably the other six tocopherols and tocotrienols, as well. Balanced antioxidant supplementation is always preferable to a high dose of a single antioxidant.
Winterbone MS, Sampson MJ, Saha S, Hughes JC, Hughes DA. Pro-oxidant effect of alpha-tocopherol in patients with type 2 diabetes after an oral glucose tolerance test--a randomised controlled trial. Cardiovasc Diabetol. 2007 Feb 22;6:8.