A study in the journal JAMA found that patients with mild Alzheimer's disease and levels of vitamin E were given at high dose levels of memory decline more slowly than those given a placebo or dummy pill.
They are able to carry out the tasks of daily periods longer and require less assistance from the guards, said a researcher in the United States.
But experts who are members of the Alzheimer's Society said the doses used are very high and may not be safe.
In the study, 613 people with mild to moderate Alzheimer's receiving daily doses of vitamin E. The patient is undergoing therapy dementia drugs known as memantine, which is a combination of vitamin E and memantine, and others are given a placebo.
Changes in their ability to carry out everyday tasks - such as washing or changing clothes - measured average for more than two years.
"These findings suggest that alpha- tocopherol is beneficial in mild to moderate Alzheimer's by slowing functional decline and reduce the burden on caregivers," said a team led by Dr. Maurice Dysken of the Minneapolis VA Health Care System.
Commenting on the study, Dr Doug Brown, director of research and development at the Alzheimer's Society, said the treatments that can help people with dementia carry out everyday tasks is the key to enable these people to live in a good condition as long as possible.
But he said more research is needed to see whether vitamin E actually have benefits for people with dementia, and is it safe taking high doses every day.