An ample body of research has shown that oxidative stress plays a key role in the development of neurodegenerative disorders such as Alzheimer’s and Parkinson’s disease. As a result, antioxidant supplements have been proposed as preventive measures against dementia. A new trial, however, tests the effect of vitamin E and selenium on aging men and finds no evidence that they have therapeutic value.

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New research investigates the effects of antioxidant supplements on dementia and does not recommend vitamin E or selenium as preventive agents.

In neurodegenerative disorders such as Alzheimer’s disease or Parkinson’s disease, brain cells die slowly but irreversibly. While researchers do not know exactly what causes dementia and other neurodegenerative conditions, the process of oxidative stress has been shown to play a key role.

Oxidative stress is a process commonly associated with advancing age. It is a form of physiological damage on the body caused by an accumulation of free radicals.

A healthy body normally maintains a balance between free radicals and antioxidants, but when free radicals are found in overwhelming numbers, our body’s lipids, proteins, and DNA are damaged, thus causing a number of diseases.

Therefore, some studies have suggested that an intake of antioxidants from dietary supplements may help to restore the body’s antioxidant/free radicals balance, with a specific focus on the benefits of antioxidants on cognitive impairment.

Vitamin E and selenium have both been shown to have antioxidant properties. A new study – by Richard J. Kryscio, Ph.D., of the University of Kentucky in Lexington, and his colleagues – presents the results of a clinical trial that examined the ability of these two supplements to ward off dementia in asymptomatic older men.

The findings were published in JAMA Neurology.

The Prevention of Alzheimer’s Disease by Vitamin E and Selenium (PREADViSE) is a double-blind, randomized clinical trial that began in May 2002.

PREADViSE was part of the Selenium and Vitamin E Cancer Prevention Trial (SELECT), designed to test the effects of vitamin E and selenium on prostate cancer.

SELECT closed in 2009, and the remaining PREADViSE trial turned into a cohort study running from September 2009 to May 2015.

The PREADViSE trial included 7,540 men aged 60 and above, 3,786 of whom carried on to participate in the cohort study. During the trial, the men were randomly assigned to receive vitamin E, selenium, a combination of the two, or a placebo.

Throughout the trial, as well as in the cohort study, the participants were assessed for dementia using a two-stage screen, and they were encouraged to see a physician for a checkup if the results suggested the possibility of cognitive impairment.

Finally, the scientists used Cox proportional hazards models to adjust for race, ethnicity, and other demographic information, as well as for the presence of comorbidities.

The study found that neither of the two supplements, either taken alone or in combination, prevented dementia.

The authors note that to their knowledge, this is the first study that examines the long-term effect of antioxidant supplements on dementia in asymptomatic men. Kryscio and colleagues also admit some of the study’s limitations – for example, the fact that it lost half of its participants during the transition to a cohort study. Additionally, the researchers point out that the randomized trial and cohort study may have also been biased by the publicity around the adverse effects of supplements.

The authors conclude:

The supplemental use of vitamin E and selenium did not forestall dementia and are not recommended as preventive agents. This conclusion is tempered by the underpowered study, inclusion of only men, a short supplement exposure time, dosage considerations and methodologic limitations in relying on real-world reporting of incident cases.”

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