Oxidative stress has long been linked to age-related cognitive decline, the harbinger of dementia. Epidemiologic studies relating adherence to antioxidant-rich dietary patterns to lower incidence of cognitive impairment provide supportive evidence for the oxidative hypothesis of cognitive decline.

Walnuts are rich in alpha-linolenic acid, a plant-based omega-3 fatty acid. Walnuts also possess more polyphenolic compounds than any other type of nut. Both omega-3 fatty acids and polyphenols are considered critical brain foods that may counteract oxidative stress and inflammation, two drivers of cognitive decline. Hence, walnuts could beneficially influence cognition.

A two-center (Barcelona, Spain and Loma Linda, California) randomized controlled trial examined the cognitive effects of a two-year walnut intervention in initially cognitively healthy elders. The study, published in The American Journal of Clinical Nutrition, consisted of 708 free-living elders randomly assigned to a diet enriched with walnuts (30-60g/d) or without. A battery of comprehensive neurocognitive tests was administered at baseline and two years. In addition, repeated structural and functional brain magnetic resonance (fMRI) imaging was performed on a subset of 108 Barcelona participants.

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Of the 636 participants that completed the 2-year study, walnut supplementation had no overall effect on cognition. However, analysis of results by site and fMRI findings in Barcelona participants, who displayed lower education and a lower background status of dietary alpha-linolenic acid compared to the Loma Linda counterparts, suggest that walnuts might delay cognitive decline in subgroups at higher risk. “These results are encouraging but not conclusive for an effect of walnuts on brain health,” said Emilio Ros, from Hospital Clinic in Barcelona, and colleagues who conducted the study. Further investigation is warranted, in particular for disadvantaged populations in whom greatest benefit could be expected. 

Reference Sala-Vila A, Valls-Pedret C, Rajaram S, Coll-Padrós N, Cofán M, Serra-Mir M, Pérez-Heras AM, Roth I, Freitas-Simoes TM, Doménech M, Calvo C, López-Illamola A, Bitok E, Buxton NK, Huey L, Arechiga A, Oda K, Lee GL, Corella D, Vaqué-Alcázar L, Sala-Llonch R, Bartrés-Faz D, Sabaté J, Ros E. Effect of a two-year diet intervention with walnuts on cognitive decline. The Walnuts And Healthy Aging (WAHA) study: a randomized controlled trial.  The American Journal of Clinical Nutrition, DOI: https://doi.org/10.1093/ajcn/nqz328.  

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