Abstract
Background
Vitamin E is a dietary compound that functions as an antioxidant scavenging toxic free radicals. Evidence that free radicals may contribute to the pathological processes of cognitive impairment including Alzheimer’s disease has led to interest in the use of vitamin E in the treatment of mild cognitive impairment (MCI) and Alzheimer’s dementia (AD).
Objectives
To assess the efficacy of vitamin E in the treatment of AD and prevention of progression of MCI to dementia.
Search methods
The Specialized Register of the Cochrane Dementia and Cognitive Improvement Group (ALOIS), The Cochrane Library, MEDLINE, EMBASE, PsycINFO, CINAHL, LILACS as well as many trials databases and grey literature sources were searched on 25 June 2012 using the terms: “Vitamin E”, vitamin-E, alpha-tocopherol.
Selection criteria
All unconfounded, double-blind, randomised trials in which treatment with vitamin E at any dose was compared with placebo for patients with AD and MCI.
Data collection and analysis
Two review authors independently applied the selection criteria and assessed study quality and extracted and analysed the data. For each outcome measure data were sought on every patient randomised. Where such data were not available an analysis of patients who completed treatment was conducted. It was not possible to pool data between studies owing to a lack of comparable outcome measure.
Main results
Only three studies met the inclusion criteria: two in an AD population and one in an MCI population. In the first of the AD studies (Sano 1996) the authors reported some benefit from vitamin E (2000 IU/day) with fewer participants reaching an end point of death, institutionalisation, change to a Clinical Dementia Rating (CDR) of three, or loss of two basic activities of daily living within two years. Of patients completing treatment, 58% (45/77) on vitamin E compared with 74% (58/78) on placebo reached one of the end points (odds ratio (OR) 0.49; 95% confidence interval (CI) 0.25 to 0.96). The second AD treatment study (Lloret 2009) explored the effects of vitamin E (800 IU/day) on cognitive progression in relation to oxidative stress levels. Patients whose oxidative stress markers were lowered by vitamin E showed no significant difference in the percentage change in Mini-Mental State Examination (MMSE) score, between baseline and six months, compared to the placebo group. The primary aim of the MCI study (Petersen 2005) was to investigate the effect of vitamin E (2000 IU/day) on the time to progression from MCI to possible or probable AD. A total of 214 of the 769 participants progressed to dementia, with 212 being classified as having possible or probable AD. There was no significant difference in the probability of progression from MCI to AD between the vitamin E group and the placebo group (hazard ratio 1.02; 95% CI 0.74 to 1.41; P = 0.91).
Authors’ conclusions
No convincing evidence that vitamin E is of benefit in the treatment of AD or MCI. Future trials assessing vitamin E treatment in AD should not be restricted to alpha-tocopherol.
Plain language summary
Vitamin E should not be used for the treatment of mild cognitive impairment (MCI) and Alzheimer’s dementia (AD)
Vitamin E is a dietary compound that has strong antioxidant properties. Vitamin E has been shown to act on some toxic chemicals that may contribute to the damage seen in AD. Many laboratory, animal and epidemiological studies have pointed towards a possible beneficial role for vitamin E in the prevention and treatment of AD. However, to date very limited evidence exists in humans to support the routine use of vitamin E. Further, in recent years evidence has come to light implicating vitamin E with potentially serious side effects and even increased mortality. In this review three studies were identified and these demonstrated no or limited benefit for vitamin E in MCI and AD. Therefore, vitamin E should not be used in the treatment of MCI or AD. More trials are still needed but these should include different forms of vitamin E.
