Urinary urolithins and cortical thickness in walnut-trial MRI substudy
In 104 cognitively healthy older adults, rising urinary urolithins tracked with preserved cortical thickness over 2 years, mainly in the right hemisphere and more clearly in metabotype B. This is an association, not proof of cause. [1]
Automatic summary · not editorially reviewed
The key findings
This longitudinal MRI substudy was conducted within the Walnuts and Healthy Aging randomized controlled trial, which tested 2 years of daily walnut consumption versus a control diet in older people at two centers. [1]
Among 55 participants allocated to the walnut diet, greater increases in urolithin A and urolithin C were longitudinally associated with preservation of cortical thickness, mainly in right-hemisphere regions and more pronounced in metabotype B. [1]
The authors present the findings as clinical evidence linking microbiota-derived (poly)phenol metabolites to brain aging and supporting a precision nutrition framework. [1]
The source at a glance
- Study type / format
- Longitudinal MRI substudy within a two-center randomized controlled trial (abstract)
- Population / context
- 104 cognitively healthy older adults from the Barcelona center of the Walnuts and Healthy Aging trial; 55 were allocated to the walnut diet.
- Summary based on
- Study abstract
- Original publication
- October 7, 2026
Walnut-trial MRI substudy in Barcelona participants
This longitudinal MRI substudy was part of the Walnuts and Healthy Aging study, a two-center randomized controlled trial in Barcelona, Spain and Loma Linda, California. The trial tested 2 years of daily walnut consumption against a control diet for age-related health outcomes in older people. A subset from the Barcelona center had structural MRI at baseline and after 2 years. The authors asked whether changes in urinary urolithins, gut microbiota-derived metabolites of walnut ellagitannins, were associated with concurrent changes in cortical thickness, a biomarker of age-related neurodegeneration.
Supporting source [1]
Urolithin rises linked to preserved cortical thickness
Of 104 participants, 55 were allocated to the walnut diet. In that group, greater increases in urolithin A (β = 0.023 per 1-SD, 95% CI 0.003–0.043) and urolithin C (β = 0.015, 95% CI 0.002–0.031) were longitudinally associated with preservation of cortical thickness, predominantly in right-hemisphere regions. Associations were more pronounced among metabotype B individuals. Urinary urolithins were measured by liquid chromatography–high-resolution mass spectrometry, and changes were related to concurrent cortical-thickness changes using multivariable-adjusted linear regression, stratified by urolithin metabotype.
Supporting source [1]
Abstract-only scope: associations, not causal proof
The authors describe these as novel clinical evidence linking microbiota-derived (poly)phenol metabolites to brain aging and supporting a precision nutrition framework. However, the design relates changes in urolithins to concurrent changes in cortical thickness; it does not show that urolithins cause the structural differences. Only the abstract was reviewed, so details such as the full participant flow, the control-group results and the full statistical reporting were not inspected. The trial is registered as NCT01634841.
Supporting source [1]
How to interpret this
Abstract only; the full text was not reviewed. The design is observational within a trial: urolithin changes are associated with concurrent cortical-thickness changes, not shown to cause them. Full participant flow, control-group findings and complete statistical reporting were not inspected.
Based on the study abstract; the full paper, tables and supplementary data were not reviewed.
Source & supporting passages
Galkina P, Domínguez-López I, Cofán M, Pozzoli C, Vallverdú-Queralt A, Serra-Mir M, Chiva-Blanch G, Rajaram S, Sabaté J, Sala-Vila A, Ros E, Lamuela-Raventós RM. · europepmc.org · October 7, 2026