Article - Polyphenol supplementation and executive functioning in overweight and obese adults at risk of cognitive impairment: A systematic review and meta-analysis.

Expert Review

Reviewer: Ana-Paula Agrela

15th Feb 2024

Conflict of interest

None

Take home message

Overweight and obesity have increasing evidence that indicates a link to compromised executive functions such as memory and decision-making processes and cognitive impairment
This meta-analysis revealed a non-significant effect of polyphenol supplementation on executive functions among overweight and/or obese populations with a susceptibility to cognitive impairment.

Evidence category

B: Systematic reviews including RCTs of limited number

Summary review

A systematic review and meta-analysis were undertaken to investigate the impact of polyphenol supplementation on executive functions (cognitive functions which constitute part of the working memory and decision-making processes) among overweight and/or obese populations.

Method: A comprehensive literature search was conducted using four electronic databases: PubMed/Medline, PsycInfo, Scopus and the Cochrane Trials Library. Inclusion criteria encompassed primary research studies which investigated the impact of polyphenols versus placebo on executive function in overweight or obese adults.

The review comprised a total of 23 randomised controlled trials (RCTs), incorporating a participant pool of N = 1,976 individuals. The mean ages of participants in all 23 studies receiving polyphenol supplementation were 62.92 years (SD = 8.06 years) and the mean BMIs ranged from 25.5 kg/m2 to 33.7 kg/m2. Various dietary polyphenols were investigated in the studies, with the main groups being isoflavones, flavonoids, resveratrol, phenolic acid, curcumin, walnuts and blueberry powder.

The JADAD scale was employed to assess the methodological quality of the incorporated studies
Hedges g, accompanied by 95% confidence intervals (CI) for endpoints, was computed utilising a random effects model whenever applicable
Various statistical methods were considered for potential application in evaluating publication bias
Sensitivity analysis was conducted to assess the robustness of the obtained results.

Results

Meta analysis of the 23 primary studies produced a non-significant effect of polyphenol supplementation on executive function (g = 0.076, CI = -0.018 to 0.170)
A double-blind, randomised, placebo-controlled parallel study reported significant benefits in 60 participants (mean age 67 years) taking 80mg of curcumin over placebo for digital vigilance and serial subtraction tasks (p=0.041)
A double-blind, randomised, placebo-controlled parallel intervention trial showed significant benefits in 79 patients (mean age of 61 years) taking 150mg of resveratrol for visuospatial working memory double span and trail making test (p= 0.012).

Conclusion: This meta-analysis revealed a non-significant effect of polyphenol supplementation on executive functions among overweight and/or obese populations.

Clinical practice applications

Research has documented the association between compromised executive functions and obesity/overweight, emphasising neuroinflammation and oxidative stress as potential mechanisms
A plausible intervention involves the utilisation of polyphenols, known for their antioxidant and anti-inflammatory properties
This systematic review and meta-analysis revealed a non-significant effect of polyphenol supplementation on executive functions
A potential beneficial impact for 80mg of curcumin and 150mg of resveratrol was revealed in younger populations (mean ages of 67 and 61 years).

Considerations for future research

A potential beneficial impact of 80mg of curcumin and 150mg of resveratrol supplementation was revealed in a younger population (mean ages of 67 and 61 years), highlighting the necessity for in-depth exploration in subsequent studies
The diversity in tasks employed for assessing executive functions and the comprehensive reporting of the phenolic composition of supplements had limitations that warrant consideration in future research
The exact constituent and dose of supplementation needs to be described as this is necessary for the identification of the potential beneficial compounds for cognitive health and to support clinical practice.

Expert reviews are written by nutrition professionals and academics with advanced qualifications to provide a critical appraisal of the article and implications for practice. Each review is peer-reviewed by a member of the NED Editorial Board. Find out more about our NED Expert Reviewers here.

Abstract

BACKGROUND AND OBJECTIVES

Increasing evidence indicates a link between obesity and cognitive impairment. Furthermore, there is limited literature regarding the effect of polyphenols, a plant derived compounds, on executive functioning in an overweight/obese population at-risk of cognitive impairment. The aim of the present systematic review and meta-analysis of randomized controlled trials is to examine the effect of polyphenol supplementation on executive functions in overweight and/or obese populations at risk of cognitive impairment.

METHODS

A comprehensive literature search was conducted from inception to March 2023 using four electronic databases: PubMed/Medline, PsycInfo, Scopus and Cochrane trials library. Published primary research studies in English that compared the effect of polyphenols with placebo on executive function in overweight/obese adults were considered eligible for the meta-analysis. Jadad scale was used for the methodological quality rating of the included studies. Hedges g with 95% confidence intervals (CI) for endpoints were calculated using random effect model where applicable. Rosenthal's Fail-safe N, funnel plots, the Begg and Mazumdar's rank correlation test (Kendall's S statistic P-Q), Egger's linear regression test, and Duval and Tweedie's trim-and-fill test were identified for potential use as appropriate, to examine publication bias. Sensitivity analysis was conducted to examine the robustness of the results.

RESULTS AND CONCLUSION

A total of 23 RCT studies involving N = 1,976 participants were included in the review. The results of the meta-analysis revealed a non-significant effect for polyphenol supplementation on executive function (g = 0.076, CI = -0.018 to 0.170). Observations from primary studies within the meta-analysis showed a potential positive effect of polyphenol supplementation in a younger population at-risk of cognitive impairment and it is recommended to investigate this further in future studies. Moreover, the variability of the tasks used to examine executive functions as well as the adequate reporting of supplement's phenolic composition is a limitation that future work should also consider.

Copyright: © 2023 Farag et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.