Longer-term mixed nut consumption improves brain vascular function and memory: A randomized, controlled crossover trial in older adults

Abstract

Nut consumption may reduce age-related cognitive decline, but underlying mechanisms are unclear. To investigate in older adults longer-term effects of mixed nut consumption on brain vascular function, which may underlie improvements in cognitive performance. Twenty-eight healthy individuals (age [mean±SD]: 65±3 years; BMI: 27.9±2.3kg/m2) were included in a randomized, single-blinded, cross-over trial with a 16-week intervention (60g/d mixed nuts: walnuts, pistachio, cashew, and hazelnuts) and control period (no nuts), separated by 8 weeks of washout. Participants followed the Dutch food-based dietary guidelines. At the end of each period, cerebral blood flow (CBF), a marker of brain vascular function, was quantified using arterial spin labeling magnetic resonance imaging. Effects on endothelial function, arterial stiffness, and the retinal microvasculature were also assessed. Cognitive performance was measured using the Cambridge Neuropsychological Test Automated Battery. Body weight remained stable during the study. As compared to the control period, the mixed nut intervention resulted in a higher regional CBF in the right frontal and parietal lobes (treatment effect: 5.0±6.5mL/100g/min; P<0.001), left frontal lobe (5.4±7.1mL/100g/min; P<0.001), and bilateral prefrontal cortex (5.6±6.6mL/100g/min; P<0.001). Carotid artery reactivity (0.7PP; 95%CI: 0.2 to 1.2; P=0.007), brachial flow-mediated vasodilation (1.6PP; 95%CI: 1.0 to 2.2; P<0.001) and retinal arteriolar calibers were higher (2μm; 95%CI: 0 to 3; P=0.037), and carotid-to-femoral pulse wave velocity lower (-0.6m/s; 95%CI:-1.1 to-0.1; P=0.032). Further, visuospatial memory (-4 errors [16%]; 95%CI:-8 to 0; P=0.045) and verbal memory (+1 correct [16%]; 0 to 2; P=0.035) improved, but executive function and psychomotor speed did not change. Longer-term mixed nut consumption as part of a healthy diet beneficially affected brain vascular function, which may relate to the observed beneficial effects on memory in older adults. Moreover, different characteristics of the peripheral vascular tree also improved.