Abstract
Context: As the food industry is continually involved in the development of new attractive alternative therapeutic agents, the evaluation of the beneficial impact of (poly)phenols on cognitive and brain function during aging has gained increasing interest. Objective: This systematic review and meta-analysis aimed to evaluate the acute and chronic effects of (poly)phenol-rich diet supplementation on cognitive function and brain health in aging adults. Data Sources: PubMed and Web of Science databases were searched for relevant randomized placebo-controlled trials (RCTs) published from inception to July 2019. Study Selection: Two researchers independently screened 4303 records, using the PICOS criteria: Participants were aging adults; Intervention was based on acute and/or chronic (poly)phenols-rich supplementation; Comparator was any comparator; Outcomes included cognitive function and neuroprotective measures; and Study design was RCTs. A third researcher was consulted when discrepancies arose. Fifteen high-quality (mean PEDro score = 8.8 ± 0.56) RCTs (total participants: 918 healthy older adults) were included in the final sample. Data Extraction: Information on study design, employed treatment, characteristics of participants, outcomes, and the correspondent assessing methods were extracted. Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed. Data Analysis and Results: A random-effects meta-analysis was used to pool estimates across studies. Effect size (ES) and its 95% confidence interval (CI) was calculated. Pooled results yielded a trivial ES (−0.2 to 0.03) for brain-derived neurotrophic factor and neuroinflammatory parameters and small (0.36) to moderate (0.82) ES for executive functions. Conclusion: This meta-analysis failed to provide evidence regarding the neuroprotective and anti-inflammatory effect of (poly)phenols supplementation in aging adults. However, findings from individual studies, included in this systematic review, suggest polyphenol-rich supplementation may improve some cognitive and brain functions in older adults. The beneficial effect of polyphenols seems to depend on ingested dose and bioavailability. Results suggest at least an intermediate dose (≥500 mg), and intermediate (≈9%) to high (43%) bioavailability rates are needed to cross the brain blood barrier and to exert a significant effect on cognitive health.
Highlights
For the first time in history, most people can expect to live into their sixties and beyond [1]
The present results of the pooled analysis failed to demonstrate any anti-inflammatory action of chronic anthocyanin [31] and resveratrol [29,42] supplementation on Hs-CRP and/or IL-6 and TNF-α. These results indicate that the employed dose (200 mg to 387 mg) and the bioavailability of the used polyphenol compound (e.g., 0.4 for anthocyanin) of the included studies were not sufficient to exert anti-inflammatory effects
The evaluation of the beneficial impact ofphenols on cognitive and brain function during aging has recently garnered increased interest as food industries are continually involved in developing new attractive alternative therapeutic agents
Summary
For the first time in history, most people can expect to live into their sixties and beyond [1]. The redox imbalance in favor of pro-oxidant in older adults is mainly due (i) to the increased generation of reactive oxygen species because of the higher accumulation of reactive iron with aging [10,11] and (ii) to the decreased activity of many antioxidant enzymes (i.e., superoxide dismutase, catalase, glutathione, and glutathione peroxidase) in specific cognitive regions of the brain such as the hippocampus and the cerebral cortex [12,13] This imbalance reduces the brain’s capability to neutralize/counter the generated free radicals (FR) and, increases vulnerability to FR attack, potentially leading to tissue damage and neuroinflammatory processes [14,15]. This may play an important role in the apparition of neurodegenerative disease via toxin generation pathways [9,18]
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