The Impact of the Mediterranean Diet on the Cognitive Functioning of Healthy Older Adults: A Systematic Review and Meta-Analysis

Abstract

Evidence from epidemiologic studies suggests a relation between the Mediterranean diet (MeDi) and cognitive function, but results are inconsistent. Prior reviews have not provided pooled data from meta-analysis of longitudinal studies and randomized controlled trials (RCTs), or they included younger adult participants. This systematic review and meta-analysis examines the impact of the MeDi on the cognitive functioning of healthy older adults. Fifteen cohort studies with 41,492 participants and 2 RCTs with 309 and 162 participants in intervention and control groups, respectively, were included. The primary outcome of interest was cognitive function, divided into domains of memory and executive function. Meta-analysis of cohort studies revealed a significant association between MeDi and older adults' episodic memory (n = 25,369, r = 0.01, P = 0.03) and global cognition (n = 41,492, r = 0.05, P ≤ 0.001), but not working memory (n = 1487, r = 0.007, P = 0.93) or semantic memory (n = 1487, r = 0.08, P = 0.28). Meta-analysis of RCTs revealed that compared with controls, the MeDi improved delayed recall (n = 429, P = 0.01), working memory (n = 566, P = 0.03), and global cognition (n = 429, P = 0.047), but not episodic memory (n = 566, P = 0.15), immediate recall (n = 566, P = 0.17), paired associates (n = 429, P = 0.20), attention (n = 566, P = 0.69), processing speed (n = 566, P = 0.35), or verbal fluency (n = 566, P = 0.12). The strongest evidence suggests a beneficial effect of the MeDi on older adults' global cognition. This article discusses the influence of study design and components of the MeDi on cognitive function and considers possible mechanisms.

Keywords: Mediterranean diet; cognitive functioning; healthy older adults; meta-analysis; systematic review.

FIGURE 1

Preferred Reporting Items for Systematic Reviews and Meta-Analyses flow diagram. RCT, randomized controlled trial.

FIGURE 2

Forest plots for observational studies showing plots for episodic memory (A), global cognition (B), and semantic memory (C).

FIGURE 3

Forest plots for randomized controlled trials showing plots for attention (A), delayed recall (B), episodic memory (C), global cognition (D), immediate recall (E), paired associates (F), processing speed (G), verbal fluency (H), and working memory (I).CG, control group; EG, experimental group; MD, Mediterranean Diet; N, nuts; OO, olive oil.