VITAMINS & SUPPLEMENTS · GUIDE
Antioxidants, Cognition and Dementia Risk: What Trials Found
What randomized trials and Cochrane reviews found for vitamin E, vitamin C, beta-carotene and selenium on memory, cognitive decline and dementia, and what stays uncertain.
Content last updated . This page has not been medically reviewed.
Back to AntioxidantsQuick answer
The PREADViSE authors describe oxidative stress as an established dementia pathway, which is one reason antioxidant supplements were tested. [1] The results are mostly disappointing. In cognitively healthy older adults, a Cochrane review did not find evidence that any vitamin or mineral supplementation strategy has a meaningful effect on cognitive decline or dementia, though it said the evidence does not permit definitive conclusions. [2] The one clearer finding is narrow: in people who already had Alzheimer's disease, one trial of high-dose vitamin E found slower decline in daily functioning. [3] That does not transfer to healthy people, to other forms of vitamin E, or to other antioxidants.
Evidence labels used here: mixed, no good evidence of benefit, promising but limited, evidence of harm. Memory problems should be assessed by a clinician; see mild cognitive impairment and dementia.
What the trials found
| Group studied | Study and amount (study amounts, not advice) | What the source found | Label |
|---|---|---|---|
| Healthy older adults, many reviews pooled | Cochrane review: 28 studies, more than 83,000 participants; 8 studies (47,840 participants) tested beta-carotene, vitamin C or vitamin E [2] | Results were mixed; the only positive signals came from long-term antioxidant vitamin studies, and the authors did not find a meaningful effect on cognitive decline or dementia overall [2] | Mixed, low certainty |
| Men aged 60 and older, no memory complaints | PREADViSE: 7540 men, vitamin E, selenium, both, or placebo [1] | Dementia was not different among the four arms; neither supplement prevented dementia [1] | No good evidence of benefit |
| Women aged 65 and older with or at risk of heart disease | Women's Antioxidant Cardiovascular Study: vitamin E 402 mg every other day, beta-carotene 50 mg every other day, vitamin C 500 mg daily; tested by telephone over 5.4 years [4] | Antioxidant supplementation did not slow cognitive change [4] | No good evidence of benefit |
| Mild cognitive impairment (MCI) | Cochrane review of vitamin E (alpha-tocopherol form) in MCI and Alzheimer's dementia [5] | No evidence it prevents progression to dementia or improves cognition in MCI [5] | No good evidence of benefit |
| Mild to moderate Alzheimer's disease | TEAM-AD: 613 patients already taking a cholinesterase inhibitor; 2000 IU a day of alpha tocopherol vs placebo [3] | Slower decline in daily functioning than placebo [3]. The Cochrane review found no clinically important effect on cognition scores in Alzheimer's, but moderate-quality evidence from one study that it may slow functional decline [5] | Promising but limited, in this group only |
| Moderately severe Alzheimer's disease | Earlier trial: alpha-tocopherol 2000 IU a day, selegiline, both or placebo [6] | Unadjusted analyses showed no significant difference among the four groups; adjusted analyses showed delays [6] | Mixed |
How to read these results
- Specific form and amount. The positive Alzheimer's findings used the alpha-tocopherol form at 2000 IU a day. [3] The NHS lists 540 mg (800 IU) or less a day of vitamin E supplements as unlikely to cause harm, so this is a high study amount. [7]
- Different questions. Treating people with dementia, delaying MCI, and preventing dementia in healthy people are separate questions. Success in one is not evidence for another.
- Small signals. A Cochrane review found low-certainty hints of better cognition with beta-carotene after about 18 years and vitamin C after 5 to 10 years. [2] NCCIH describes the effects seen as small. [8]
- Food versus pills. NCCIH says higher intakes of vegetables and fruits go with lower risks of chronic disease, but there is currently no evidence that antioxidant supplements have a positive impact on these diseases, apart from age-related macular degeneration. [8]
Safety and who should ask first
- Vitamin E and bleeding. High doses of vitamin E supplements may increase the risk of bleeding and may interact with anticoagulant or antiplatelet medicines. [8] See medication interactions and supplements before surgery.
- Prostate cancer signal. One study in the Cochrane review of healthy adults found a statistically significant increase in prostate cancer diagnoses among men taking vitamin E. [2]
- Beta-carotene. NCCIH reports that beta-carotene supplements increased lung cancer risk, most strongly in people at high risk such as smokers and those exposed to asbestos at work. [8] See beta-carotene supplements, smokers and the ATBC and CARET trials.
- Older adults. A clinician or pharmacist can review any supplement against a person's medicines; see older adults.
Proper evidence not found
For CoQ10, alpha-lipoic acid, polyphenol extracts or glutathione and dementia outcomes, proper evidence not found in the sources we read. Our searches covered vitamin E, vitamin C, beta-carotene, selenium and antioxidants with cognition and dementia; we did not search the other compounds one by one. For other brain-supplement claims see nootropic evidence by outcome.Related pages
Vitamin E, selenium, and brain-healthy habits.Frequently asked questions
Can antioxidant supplements prevent dementia?
A Cochrane review did not find evidence that any vitamin or mineral supplementation strategy for healthy adults in mid or late life has a meaningful effect on cognitive decline or dementia. [2] In PREADViSE, neither vitamin E nor selenium prevented dementia. [1]
Does vitamin E help Alzheimer's disease?
In one trial of people with mild to moderate Alzheimer's disease who were taking a cholinesterase inhibitor, 2000 IU a day of alpha tocopherol slowed functional decline. [3] The Cochrane review found no clinically important cognition benefit. [5] Ask a clinician before using vitamin E alongside any medicine.
Does vitamin E stop mild cognitive impairment turning into dementia?
The Cochrane review found no evidence that the alpha-tocopherol form prevents progression from MCI to dementia. [5]
Is the 2000 IU study amount a safe amount to take?
It is a study amount, not advice. The NHS says 540 mg (800 IU) or less a day of vitamin E supplements is unlikely to cause harm. [7] High-dose vitamin E may affect bleeding and interact with some medicines. [8]
If antioxidant foods are linked with better health, why do pills not help?
NCCIH says purified antioxidants might act differently than those consumed in foods, and other substances or habits linked with eating fruits and vegetables may explain the link. [8]
References
- Kryscio RJ, et al. Association of antioxidant supplement use and dementia in the Prevention of Alzheimer's Disease by Vitamin E and Selenium Trial (PREADViSE). JAMA Neurol. 2017. Read 2026-10-23.
- Rutjes AWS, et al. Vitamin and mineral supplementation for maintaining cognitive function in cognitively healthy people in mid and late life. Cochrane Database Syst Rev. 2018. Read 2026-10-23.
- Dysken MW, et al. Effect of vitamin E and memantine on functional decline in Alzheimer disease: the TEAM-AD VA cooperative randomized trial. JAMA. 2014. Read 2026-10-23.
- Kang JH, et al. Vitamin E, vitamin C, beta carotene, and cognitive function among women with or at risk of cardiovascular disease: the Women's Antioxidant and Cardiovascular Study. Circulation. 2009. Read 2026-10-23.
- Farina N, et al. Vitamin E for Alzheimer's dementia and mild cognitive impairment. Cochrane Database Syst Rev. 2017. Read 2026-10-23.
- Sano M, et al. A controlled trial of selegiline, alpha-tocopherol, or both as treatment for Alzheimer's disease. N Engl J Med. 1997. Read 2026-10-23.
- Vitamins and minerals: Vitamin E. NHS (UK), page last reviewed 3 August 2020. Read 2026-10-23.
- Antioxidant Supplements: What You Need To Know. National Center for Complementary and Integrative Health (US). Read 2026-10-23.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.