Effects of Nutrition on Cognitive Function in Adults with or without Cognitive Impairment: A Systematic Review of Randomized Controlled Clinical Trials

Nutrients
Q1
Oct 2021
Citations:62
Influential Citations:1
Systematic Reviews / Meta-Analyses
84
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Methods
Systematic review of randomized controlled trials (including crossover and parallel designs) evaluating dietary interventions (diet counseling, food-based interventions, and dietary supplement trials) in adults with or without cognitive impairment, excluding diagnosed Alzheimer’s disease; age range 18–90 years; trials conducted in 18 countries; 61 articles included; cognitive outcomes assessed via neuropsychological tests and imaging; quality assessed with RoB 2; PRISMA guidelines; PROSPERO registration (CRD42021245941).
Results
Across eligible trials, significant cognitive improvements were observed in 44 of 61 studies, across dietary patterns, foods, and supplements; 17 showed no significant improvement. Mediterranean-style patterns (e.g., MedPork/MedDairy/high-phenolic EVOO) and plant-based/antioxidant-rich supplements showed the most consistent signals for improvements in processing speed, memory, attention, language and executive function, though heterogeneity and study design limitations exist. Vitamin D and B vitamins yielded mixed results; some benefits in MCI with Vitamin D3 and B9+B12 combos, but not consistently across healthy individuals. Omega-3 PUFA trials largely showed no clear benefit when given alone, though some synergies with polyphenols or vitamins were reported. Polyphenol-rich compounds (curcumin, anthocyanins from Aronia/grapes/blueberries, cocoa flavanols, green tea catechins, astaxanthin, Biokesum, etc.) and other antioxidants demonstrated domain-specific improvements in memory, processing speed, attention, verbal fluency and executive function in various populations. Some trials reported improved brain perfusion or metabolic markers, but brain imaging data were limited. Overall, adopting Mediterranean-like patterns and targeted antioxidant/polyphenol-rich supplements may support cognitive function, but results are inconsistent and largely driven by small, heterogeneous trials; more robust long-term RCTs are needed, particularly for vitamins and PUFAs, and to clarify mechanisms via imaging/biomarkers.
Limitations
Interventions were highly heterogeneous with varying ages, regions, durations (often <12 weeks), and cognitive measures; cognitive-status classifications (MCI, SCD) were inconsistently defined and sometimes not biomarker-supported; most studies were supplement trials with small samples and high risk of bias; adherence assessment and intention-to-treat analyses were inconsistent; limited brain-imaging data; generalizability is limited by demographics and study design.

Abstract

New dietary approaches for the prevention of cognitive impairment are being investigated. However, evidence from dietary interventions is mainly from food and nutrient supplement interventions, with inconsistent results and high heterogeneity between...