Phytochemicals and Cognitive Ageing in Adults Aged ≥ 50 Years: A Systematic Review and Meta-analysis of Long-term (≥ 12 weeks) Interventions

At a glance

Design

Systematic review & meta-analysis

Search

PubMed, Embase, Scopus, PsycINFO, Cochrane Library (2016–2025)

Inclusion

RCTs of oral phytochemical interventions, 12+ weeks, adults aged 50+, validated cognitive outcomes

Risk of bias

Cochrane RoB 2 tool

Studies included

16 RCTs (N ≈ 1,700; 114 outcome observations)

Registration

PROSPERO CRD420261322655

Presented at

AAIC 2026, ExCeL London, 12–15 July 2026

From the AAIC 2026 poster · click to download the full poster (PDF)

Abstract

Background. With dementia projected to affect over 150 million people by 2050, prevention is a public health priority. The 2024 Lancet Commission identified 14 modifiable risk factors accounting for approximately 45% of cases globally, converging on oxidative stress and neuroinflammation as shared biological pathways. Dietary phytochemicals modulate these pathways and show neuroprotective effects in preclinical models, but translational evidence from randomised controlled trials (RCTs) in older adults remains fragmented. No comprehensive synthesis has examined the breadth of phytochemical interventions and cognitive domains in adults aged 50 and older while restricting to durations sufficient to capture sustained neurobiological effects.

Methods. A systematic search of PubMed, Embase, Scopus, PsycINFO, and the Cochrane Library (2016–2025) identified RCTs of oral phytochemical interventions lasting 12 or more weeks in adults aged 50 and older, with validated cognitive outcomes. Risk of bias was assessed using the Cochrane RoB 2 tool. Random-effects meta-analyses were conducted within five cognitive domains using Hedges' g, with sensitivity analyses examining the influence of risk of bias on pooled estimates.

Results. Sixteen RCTs (N ≈ 1,700; 114 outcome observations) met inclusion criteria, spanning anthocyanins, polyphenol extracts, flavonoids, carotenoids, and whole-food sources. Risk of bias was rated low in six studies, some concerns in eight, and high in two. All five domain-level pooled estimates favoured intervention. Episodic memory approached significance (g = 0.22, 95% CI [−0.01, 0.44], p = .057), with positive findings in 5/8 studies. Global cognition was non-significant in the primary analysis (g = 0.31, p = .052, I² = 88%) but became significant and homogeneous after excluding the single high-risk-of-bias outlier (g = 0.11, p = .022, I² = 0%). Executive function showed consistent small effects across six studies (g = 0.14, I² = 0%). Working memory showed no significant effect. Positive findings were disproportionately concentrated in smaller and higher-risk-of-bias studies. A convergent pattern of selective benefit in cognitively vulnerable populations emerged across independent studies using different phytochemicals and analytic frameworks.

Conclusions. Phytochemical supplementation produces small but consistent cognitive benefits in adults aged 50 and older. The convergent subgroup pattern suggests phytochemicals may act as targeted neuroprotective agents in cognitively vulnerable populations rather than broad-spectrum cognitive enhancers, positioning them as candidate components of multi-domain dementia prevention strategies. Isolated supplement trials may underestimate the true potential of dietary phytochemicals, since whole plant foods contain thousands of bioactive compounds that may act synergistically. Future prevention trials should prioritise whole-food and phytochemical-rich dietary interventions, adopt enrichment designs targeting cognitively vulnerable populations, extend follow-up durations, and incorporate biomarkers of oxidative stress and neuroinflammation. Large-scale cohorts such as the U.K. Biobank offer a complementary approach to advancing dementia prevention research at population scale.

Get the full poster

Find me at the poster session, or use the links below.

More on this research

This poster is one piece of a wider PhD programme on plant-based phytochemicals, the gut-immune-brain axis, and cognitive ageing.