Objective: To assess the effect on cognition of a controlled intervention testing Mediterranean diets (MedDiet).
Design: Randomized trial after 6.5 years of nutritional intervention.
Setting: Eight primary care centers affiliated to the University of Navarra.
Participants: A random subsample of 285 participants (95 randomly allocated to each of 3 groups) of the PREDIMED-NAVARRA trial. All of them were at high vascular risk (44.8% men, 74.1±5.7 years at cognitive evaluation). Interventions: Nutritional intervention comparing two MedDiets (supplemented with extra-virgin olive oil [EVOO] or mixed nuts) versus a low-fat control diet. Participants received intensive education to increase adherence to the intended intervention. Participants allocated to the MedDiet groups received EVOO (1 l/week) or 30 g/day of mixed nuts. Dietary habits were evaluated using a validated 137-item food frequency questionnaire (FFQ). Additionally, adherence to MedDiet was appraised using a 14-item questionnaire both at baseline and yearly thereafter.
Measurements: Cognitive performance as a main outcome and cognitive status (normal, mild cognitive impairment [MCI] or dementia) as a secondary outcome were evaluated by two neurologists blinded to group assignment after 6.5 years of nutritional intervention.
Results: Better post-trial cognitive performance versus control in all cognitive domains and significantly better performance across fluency and memory tasks were observed for participants allocated to the MedDiet+EVOO group. After adjustment for sex, age, education, apolipoprotein E genotype, family history of cognitive impairment/dementia, smoking, physical activity, body mass index, hypertension, dyslipidaemia, diabetes, alcohol and total energy intake, this group also showed lower MCI (OR=0.34 95% CI: 0.12-0.97) compared with control group. Participants assigned to MedDiet+Nuts group did not differ from controls.
Conclusion: A long-term intervention with an EVOO-rich MedDiet resulted in a better cognitive function in comparison with a control diet. However, non-significant differences were found for most cognitive domains. Participants allocated to an EVOO-rich MedDiet had less MCI than controls.