Conclusions garnered from the investigation raise questions over previous findings, which identify oxidative stress as a proven dementia pathway.
The study found no evidence that the use of antioxidant supplements could prevent the onset of dementia.
“The supplemental use of vitamin E and selenium did not forestall dementia and are not recommended as preventive agents,” the study stated.
Oxidative stress, a process also implicated in Parkinson's disease and depression, is the main mechanism often used to explain Alzheimer Disease (AD) progression.
Along with diet modification, the use of antioxidant supplements as a potential aid to cognitive impairment or dementia has been put forward.
In the past patients observed with moderate dementia saw the development of the disease slow with the use of vitamin E.
However, when used alongside other antioxidants, it was unable to demonstrate benefit in patients with AD with mild to moderate dementia.
Observational studies involving selenium have linked cognitive decline with decreased plasma selenium over time. Results of its effectiveness against AD have also been mixed.
Based at the University of Kentucky, the trial enrolled 7540 elderly men who were exposed to the supplements for an average of 5.4 years.
A subset of 3786 men agreed to be observed for up to 6 additional years.
Participants took either vitamin E, selenium, vitamin E and selenium, or a placebo.
While taking study supplements, enrolled men were evaluated for dementia using a 2-stage neurological screen.
The main finding did not demonstrate dementia incidence (4.4%) differing among the 4 study arms.
“This conclusion is tempered by the underpowered study, inclusion of only men and a short supplement exposure time,” the study attempted to explain.
“In addition, there were dosage considerations and methodologic limitations in relying on real-world reporting of incident cases."
Negative media influence
Current vitamin E dietary reference values (DRVs) as set out by The European Food Safety Authority (EFSA) recommend 13 milligrams per day (mg/day) for men and 11 mg/day for women.
Meanwhile, back in 2014, the regulatory authority set an Adequate Intake (AI) for selenium at 70 microgram (µg) per day for adults.
In trying to explain the outcomes, the authors identified the surrounding publicity concerning the negative effect of supplements.
They referred to The Selenium and Vitamin E Cancer Prevention Trial as one significant study that reported on the potentially harmful effects of vitamin E (increased prostate cancer) and selenium (potentially increased diabetes).
In addition to outside negative reports on vitamin E (increased mortality), the team suggested this created issues that have affected the conduct of both the randomised control trial (RCT) and cohort study.
In the UK, Alzheimer's disease is the most common type of dementia, affecting an estimated 850,000 people.
The World Health Organization estimated that worldwide 7.7 million new cases of dementia were anticipated each year, implying one new case every 4.1 seconds.
This means that there were 2.3 m (31%) new cases per year in Europe and 1.2 m (16%) in the Americas with peak incidence among those aged 80-89 years in these regions.
Source: JAMA Neurology
Published online ahead of print: DOI: 10.1001/jamaneurol.2016.5778
“Association of Antioxidant Supplement Use and Dementia in the Prevention of Alzheimer’s Disease by Vitamin E and Selenium Trial.”
Authors: Richard J. Kryscio, Erin L. Abner, Allison Caban-Holt, Mark Lovell, Phyllis Goodman, Amy K. Darke, Monica Yee, John Crowley, Frederick A. Schmitt.