We aimed to provide a comprehensive review of the role of nutrition in dementia development or cognitive decline associated with ageing in humans. We searched PubMed up to Feb 28, 2018, for full-text, English-language articles using “dementia”, “cognitive function”, “diet”, and “nutrition” as initial keywords. Subsequent searches were performed for each diet component separately, and we also manually searched the reference lists of identified relevant reviews. We included longitudinal studies
ReviewNutrition and prevention of cognitive impairment
Introduction
An analysis of population-based data suggested that a third of Alzheimer's disease cases worldwide might be attributable to potentially modifiable risk factors.1 Nutrition is a modifiable environmental factor that has been associated with many non-communicable diseases with connections to dementia, such as diabetes and cardiovascular disease.2, 3 Evidence suggests that lifelong nutrition might also have a direct effect on brain function. For example, longitudinal stu dies have identified associations between certain nutrients or dietary patterns and brain-volume loss4, 5 or brain integrity,6 with some clinical trials7, 8 confirming these results. Additionally, a large body of scientific evidence, mostly from observational studies, suggests a direct role for lifelong nutrition on clinical measures of cognitive status in older adults. A clear overview of the strength of the available research is thus of major importance in clinical practice because it will provide the support needed for clinicians to formulate evidence-based dietary advice for individuals at risk or those already diagnosed with some degree of cognitive impairment.
Here, we provide a comprehensive review of observational studies and clinical trials that have investigated the associations between nutrition and future cognitive decline or dementia in humans. We focus on aspects of nutrition with the strongest evidence base. Given that daily food intake might have multiple effects on health outcomes due to interactions between many foods, we start our Review with individual food components (ie, essential micronutrients or other biologically active compounds and macronutrients). We then move to food groups (which might act via multiple nutrients or food ingredients) and dietary patterns (which might act via combinations of foods). Other emerging aspects of nutrition research, such as caloric restriction, are not covered because of insufficient evidence to date.
Section snippets
B vitamins
B vitamins have been studied for their potential effect on cognitive function because of their role in homocysteine metabolism and the well established association between homocysteine concentrations and cognitive decline. Specifically, several clinical studies have found that even moderately raised (within the normal range) concentrations of homocysteine might be associated with increased risk of dementia in people older than 65 years.9 Homocysteine is produced by methylation of methionine and
Fish and seafood
Several observational studies support a potentially beneficial association between fish or seafood consumption and cognitive outcomes (figure; appendix), which is consistent with the results of a 2017 meta-analysis.61 In one study,62 a significant protective association was observed between fish consumption and dementia, but only in carriers of APOE ε4. Similarly, in a study49 that reported an overall protective effect of fish consumption on cognitive decline, results were stronger for APOE ε4
Dietary patterns
Owing to the complex biological interactions between different components of the diet, it has been proposed that the use of a whole-diet approach, through the study of dietary patterns rather than individual nutrients or food groups, might help to understand the role of diet in chronic diseases, such as cognitive impairment in elderly people.72
The Mediterranean diet is the most extensively studied dietary pattern (figure, table 2; appendix). The results of most observational studies suggest
Conclusions and future directions
Nutrition is an important modifiable risk factor of cognitive dysfunction. The existing evidence suggests that certain nutrients or food ingredients, such as some B vitamins (particularly folate), flavonoids, vitamin D, and n-3 fatty acids, have the potential to benefit cognitive function. In terms of food groups, fish (and possibly other seafood), vegetables, and to a lesser extent fruit, as well as alcohol and coffee in moderation, might protect against cognitive decline. Somehow, stronger
Search strategy and selection criteria
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Homocysteine-lowering by B vitamins slows the rate of accelerated brain atrophy in mild cognitive impairment: a randomized controlled trial
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