Some research has suggested that vitamin E and selenium supplements might lower the risk for Alzheimer’s disease, but a new long-term trial has found no evidence that they will.

The study began as a randomized clinical trial in 2002 testing the supplements for the prevention of prostate cancer. When that study was stopped in 2009 because no effect was found, 3,786 of the original 7,540 men participated in a continuing study to test the antioxidants as a preventive for Alzheimer’s.

The study, in JAMA Neurology, randomly assigned the men, whose average age was 67 at the start, to take either vitamin E, selenium, both supplements, or a placebo. By 2015, 4.4 percent of the men had dementia, but there was no difference between the groups. Neither selenium, vitamin E, nor both in combination were any more effective than a placebo.

The study controlled for age, family history of Alzheimer’s disease, education, race, diabetes and other factors.

The lead author, Richard J. Kryscio, a professor of statistics at the University of Kentucky, said that it is possible that different dosages or different types of selenium or vitamin E might show an effect.

“We could have picked the wrong version or the wrong dose,” he said. “But there’s really no evidence that these supplements will make a difference down the road in preventing dementia.”