In medicine, antioxidants are "naturally occurring or synthetic substances that inhibit or retard the oxidation of a substance to which it is added. They counteract the harmful and damaging effects of oxidation in animal tissue".
Vascular disease prevention
Initially, observational cohort cohort studies such as the Nurses' Health Study found associations between self-reported consumption of vitamin C (ascorbic acid) and vitamin E (α-tocopherol) and reductions in vascular disease.
|Vitamin E 800 IU/day||2.0% (11/546)|
|Vitamin E 400 IU/day||0.6% (3/489)|
The Cambridge Heart Antioxidant Study (CHAOS) was an early randomized controlled trial of vitamin E and in spite of having worse baseline characteritics in the vitamin E group, found "in patients with angiographically proven symptomatic coronary atherosclerosis, alpha-tocopherol treatment substantially reduces the rate of non-fatal MI, with beneficial effects apparent after 1 year of treatment" and no effect oncardiovascular deaths. As noted in the table, the lack of a dose-response gradient makes causation less likely. The study also had less patients in the control group for uncertain reasons in spite of randomization. This trial was published prior to trials adhering to the Consort Statement on the reporting of trials and thus readers cannot track patients through the trial's recruitment process.
In the year 2000, the HOPE study was the first negative randomized controlled trial of Vitamin E to be published. The HOPE study used 400 IU of vitamin E and followed high-risk patients for a mean of 4.5 years. At the time of the HOPE study, 1 of every 8 Americans reported taking vitamin E supplements.
Subsequent trials confirmed the HOPE study. Vitamins C (500 mg) and E (400 IU) did not benefit males in the Physicians' Health Study II randomized controlled trial which started recruitment in 1997 and followed patients for a mean of 8 years. Vitamin E did not benefit women in the Women's Health Study randomized controlled trial which began recruitment in 1992 and followed women for an average of 10.1 years.
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