Abstract

Assessed as up to date: 2012/04/06

Background

Mild cognitive impairment (MCI) is an intermediate state between normal cognition and dementia in which daily function is largely intact. This condition may present an opportunity for research into the prevention of dementia. Carbohydrate is an essential and easily accessible macronutrient which influences cognitive performance. A better understanding of carbohydrate-driven cognitive changes in normal cognition and mild cognitive impairment may suggest ways to prevent or reduce cognitive decline.

Objectives

To assess the effectiveness of carbohydrates in improving cognitive function in older adults with normal cognition or mild cognitive impairment.

Search methods

We searched ALOIS, the Cochrane Dementia and Cognitive Improvement Group Specialized Register, on 6 April 2012 using the terms: carbohydrates OR carbohydrate OR monosaccharides OR disaccharides OR oligosaccharides OR polysaccharides OR CARBS. ALOIS contains records from all major healthcare databases (The Cochrane Library, MEDLINE, EMBASE, PsycINFO, CINAHL, LILACS) as well as from many trial databases and grey literature sources.

Selection criteria

All randomised controlled trials (RCT) examining the effect of any form of carbohydrates on the cognition or daily functioning of adults aged 55 years or over with normal cognition or MCI.

Data collection and analysis

One review author selected and retrieved relevant articles for further assessment. The remaining authors independently assessed whether any of the retrieved trials should be included. Disagreements were resolved by discussion. 

Main results

One study was included. It involved 44 adults aged 60 to 80 years and compared a glucose drink with a saccharin drink, given on only a single occasion. Those receiving the glucose drink were significantly faster in completing the switching condition of the modified Stroop test (F 1, 41 = 10.47; P < 0.01) compared to those receiving the saccharin drink. Participants in the glucose group also showed a significantly smaller dual-task cost in a computerised test of divided attention compared to the placebo group (F 1, 38 = 8.49; P < 0.01, ƞ² = 0.18). As a glucose drink was administered only once, safety, global function, behaviour disturbance, and activities of daily living were not investigated in the study.

Authors' conclusions

With only one RCT included, there is insufficient evidence to base any recommendations about the use of any form of carbohydrate for enhancing cognitive performance in older adults with normal cognition or mild cognitive impairment. More studies of many different carbohydrates are needed to tease out complex nutritional issues and to further evaluate memory improvement.

Author(s)

Ooi Cheow Peng, Loke Seng Cheong, Yassin Zaitun, Hamid Tengku-Aizan

Summary

There is insufficient evidence for the use of carbohydrates to improve cognitive performance in older adults with normal or mild cognitive impairment 

Carbohydrates consist of sugars, oligosaccharides and polysaccharides. These components are found in a large range of foods and have variable effects on digestion, blood sugar levels, and their impact on health. Despite the evidence accumulated from biological and epidemiological (observational) studies and non-randomised clinical trials, only one randomised, controlled trial could be included in this review. This study had 44 participants. Participants who were given a single glucose drink showed possible momentary enhancement of cognitive performance compared to those given a saccharin drink. A safety assessment was not reported. We need more studies on different types of carbohydrates, particularly those from fruit, vegetable and whole grain sources, for older adults with normal cognition and mild cognitive impairment to understand the role of this nutrient type in the prevention or reduction of cognitive decline.

Reviewer's Conclusions

Implications for practice 

There is insufficient evidence to support the use of carbohydrates in maintaining or improving cognitive competence, which impacts on independent living in older adults with normal cognition or mild cognitive impairment.

Implications for research 

The implications for research are two-fold. First, there is a continuing potential for development of interventions for cognitive enhancement from the diversity of carbohydrate sources that are available. The second is the quality of the available studies.

The wide range of carbohydrates and their many apparent effects on cognitive functions mean that, at first sight, they might appear suitable as interventions to improve failing cognitive function in the elderly. However, identifying an effect of any individual nutrient in healthy diets is challenging because of known synergies between nutrients, the difficulty of controlling and recording dietary intake over a long period, the occurrence of insulin resistance and associated diabetes, as well as the effect of overall nutritional status. 

Since evidence available on the protective associations of a Mediterranean diet and high vegetable intake has focused on limited population groups in developed countries, confirmation of these findings in other populations, particularly in Asians, is necessary. Small effect sizes, the inappropriate use of multiple cognitive measures, and the possibility of residual confounders all need to be considered in designing these studies. If a protective association is confirmed, it is necessary to identify potential interventions that are of high impact and cost-effective in reducing the burden of dementia in the coming years. The effectiveness of such interventions at a population versus clinical level needs to be clarified. The impact of co-morbid conditions, the presence of other modifiable risk factors for cognitive decline, and the optimal age for initiation of potential interventions are also among the important issues that need to be addressed.

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