Currently it is not possible to identify any vitamin or mineral supplements that can reduce the risk of individuals with mild cognitive impairment (MCI) from developing dementia or effectively treat symptoms. An analysis on the subject was conducted by the Cochrane Dementia and Cognitive Impairment Group; the results were published in the Cochrane Database of Systematic Reviews.
The investigators sought to assess the effects of vitamin and mineral supplementation on cognitive function and the incidence of dementia in individuals who already had MCI. They performed literature searches in December 2014, July 2015, March 2016, August 2016, March 2017, and January 2018. A total of 7257 records were retrieved from the 6 searches. After de-duplication, 5211 records remained.
Included in the review were quasi-randomized placebo-controlled trials that assessed orally administered vitamin or mineral supplements in patients with a diagnosis of MCI and evaluated the incidence of dementia, cognitive outcomes, or both. The researchers were interested in studies that were applicable to the general population of older adults and thus excluded studies in which the participants had severe vitamin or mineral deficiencies.
The researchers searched for data on the primary efficacy outcomes of dementia incidence and scores on overall cognitive function. Secondary outcomes included episodic memory, executive function, speed of processing, functional performance, clinical global impression, quality of life, adverse events, and mortality. Data collection and analysis were performed according to standard Cochrane systematic review methods. The risk for bias in the included studies was evaluated using the Cochrane risk-of-bias assessment tool. The vitamins and minerals were grouped according to their putative mechanism of action, and where clinically appropriate the investigators pooled data using random-effects models.
Ultimately, 5 trials that included a total of 879 participants and explored B vitamin supplements were included. In four of the trials, the intervention involved a combination of vitamins B6, B12, and folic acid. In the fifth trial, folic acid only was evaluated. The doses used in the 5 trials varied. With respect to the primary efficacy outcomes, none of the trials reported the incidence of dementia, and the evidence on overall cognitive function was of very low quality. Little or no effect on episodic memory, executive function, speed of processing, or quality of life was reported with respect to B vitamins taken for 6 to 24 months. The evidence in these trials was either very sparse or considered to be of very low quality.
One trial of vitamin E supplementation (1000 IU of alpha-tocopherol 2 times daily) in 516 individuals was included in the review. No effect of vitamin E supplementation was found with respect to the probability of progression from MCI to Alzheimer dementia over 3 years (hazard ratio 1.02; 95% CI, 0.74-1.41).The evidence was considered to be of moderate quality.
The investigators included one trial of 256 individuals receiving combined vitamin E and vitamin C supplementation and one trial of 26 individuals receiving supplementation with chromium picolinate. In both cases, the evidence was considered to be of very low quality.
The investigators concluded that the evidence on vitamin and mineral supplementation as treatments for MCI is quite limited. Treatment with high-dose vitamin E for 3 years most likely did not decrease the risk of developing dementia, but no data are available on this outcome for other supplements. B vitamins are the only supplement to have been evaluated in >1 randomized controlled trial. Evidence from a single study that reported a reduced rate of brain atrophy in participants taking vitamin B and a beneficial effect of vitamin B on episodic memory in participants with higher serum homocysteine at baseline merits attempted replication in other studies.
McCleery J, Abraham RP, Denton DA, et al. Vitamin and mineral supplementation for preventing dementia or delaying cognitive decline in people with mild cognitive impairment. Cochrane Database Syst Rev. 2018;11:CD011905.