'Talk to GP'
"It is vitally important that people always seek advice from their doctor before considering taking supplements," he said.
"In this instance, the dosage of vitamin E taken by participants was much higher than the recommended daily allowance and was at a level that could be significantly harmful for some."
Dr Eric Karran, director of research at Alzheimer's Research UK, said the trial suggested vitamin E may modestly slow the decline in day-to-day functioning in people with mild to moderate Alzheimer's, but without having an effect on memory and thinking skills.
He said it was too early to recommend vitamin E as a treatment.
"Until the findings from this trial have been replicated, we would not encourage people to take high doses of vitamin E supplements to try to prevent or treat Alzheimer's," he added.
"If people are concerned about their vitamin intake or diet, they should talk to their GP.