It had been theorized that the vitamin, a potent antioxidant, could slow down onset of the disease although results of studies investigating its benefit have been mixed.
A study by John Hopkins researchers earlier last year found that people who took supplements of vitamin E in combination with vitamin C were less likely to develop the disease, although there was no evidence of benefit from multivitamins, or the vitamin alone.
But in the new double-blind research on 769 subjects with mild cognitive impairment, a daily dose of 2000 IU of vitamin E over three years failed to make any difference when compared with another group taking a placebo.
"There were no significant differences in the rate of progression to Alzheimer's disease between the vitamin E and placebo groups at any point, either among all patients or among apolipoprotein E 4 carriers," write the researchers in the early online article in the New England Journal of Medicine yesterday.
In an editorial in the same journal, Deborah Blacker writes that the "clear-cut negative findings for vitamin E, which is widely used despite the dearth of evidence for its efficacy, are noteworthy".
The findings were first presented at the conference on Alzheimer's Disease and Related Disorders in Philadelphia last year, when the Alzheimer's Association described the trial as "among the most anticipated studies" at the conference.
It also found that a group taking the drug donepezil had a reduced likelihood of progression to Alzheimer's disease during the first 12 months of the study.
There are nearly 18 million people with dementia in the world and the most common cause of this dementia is Alzheimer's disease. By 2025 this figure will rise to 34 million, with 71 per cent of these likely to live in developing countries, making the need for prevention crucial.