Dietary Flavonoids Consumption and Cognitive Function: A Systematic Review and Meta-analysis of Observational Studies

Associations between dietary flavonoids consumption and cognitive health have been observed in epidemiological studies, but the results were controversial. Therefore, the present meta-analysis aimed to collectively evaluate the existing evidence from observational studies and quantitatively examine the association. Included were 26 studies with 269,574 participants. Dietary flavonoids consumption was assessed by dietary surveys in these studies, individuals with lower dietary flavonoids consumption were set as the reference group. We computed pooled estimates of adjusted odds ratios (ORs) for the risk of adverse cognitive events and beta (β) values for standardized cognitive test scores, along with their 95% confidence intervals (CIs). We found that higher dietary flavonoids consumption was associated with lower risk of adverse cognitive events (pooled OR = 0.90, 95% CI: 0.83-0.98, P = 0.01) and better cognitive test performance (pooled β = 0.03, 95% CI: 0.02-0.04, P < 0.001). The dose-response analysis showed that the risk of adverse cognitive events was reduced by 2.0% (95% CI: 1.2%-2.8%, P < 0.001) for every 100 mg/day increase in dietary flavonoids consumption. Among specific adverse cognitive events, the inverse association between dietary flavonoids consumption and risk of adverse cognitive events remained significant in cognitive decline (pooled OR = 0.88, 95% CI: 0.79-0.98, P = 0.02), but not in dementia (pooled OR = 0.97, 95% CI: 0.79-1.19, P = 0.80) and Alzheimer's disease (pooled OR = 0.90, 95% CI: 0.69-1.17, P = 0.43). Among the flavonoid subclasses, significant associations were observed for anthocyanins, flavonols, flavones, and flavan-3-ols, but not for flavanones and isoflavones. This meta-analysis summarized the up-to-date results of observational studies on dietary flavonoids consumption and cognitive function, and provided supporting evidence for the potential protective effects of flavonoids and their subclasses on cognitive function.