Antioxidants May Not Ward Off Dementia After All

A variety of supplements
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Antioxidant supplements may not help ward off dementia, a new study suggests. Although previous research had suggested a possible link between the two, this latest study is one of the largest studies to investigate whether antioxidants could help ward off dementia, and found no such link.

Researchers analyzed information from more than 7,500 U.S. men ages 60 and older who were randomly assigned to take a daily vitamin E supplement, a daily selenium supplement, both supplements or a placebo. Both vitamin E and the mineral selenium are antioxidants, which means they may prevent some types of damage in cells.

The men took the supplements for about five years, on average, and during that time, the researchers followed up with them to determine which men developed dementia. After that, a subset of about 3,700 men agreed to be followed for an additional six years while they were not taking the supplements.

The study found that the rate of dementia was about the same among men who had taken the supplements for five years and those who had taken the placebo during that time. In each of the four study groups, between 4 and 5 percent of the men developed dementia during the study. [6 Big Mysteries of Alzheimer's Disease]

"The supplemental use of vitamin E and selenium did not forestall dementia," and these supplements are not recommended to prevent dementia, the researchers, from the University of Kentucky, concluded in their paper, which was published today (March 20) in the journal JAMA Neurology.

Antioxidants are thought to thwart a damaging process called oxidative stress, which is implicated in the development of dementia. Some previous studies suggested that antioxidants might improve people's cognition or reduce their risk of dementia, but subsequent studies that were more rigorously designed — including this most recent study — have failed to find a link.

However, the new study had limitations that could have affected the results, the authors said. For example, the data on the participants in the new study actually came from a larger study that looked at whether vitamin E or selenium could prevent prostate cancer, called SELECT (which stands for "Selenium and Vitamin E Cancer Prevention Trial"). But that study ended in 2009, when an analysis failed to show a benefit of the supplements, and subsequent studies suggested that vitamin E may even increase the risk of prostate cancer. When the SELECT study ended, many of the participants dropped out, and the researchers involved in the new study lost about half of their participants.

In addition, the dementia screening test used in the study might have missed some people who were in the early stages of dementia, the researchers said.

Also, most of the participants were in their 60s during the study period, and the risk of dementia is still low for people in this age group, said Dr. Steven DeKosky, of the University of Florida, and Dr. Lon Schneider, of the University of Southern California, who were not involved in the research and wrote an editorial accompanying the new study in the journal.

Original article on Live Science.

Rachael Rettner

Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.