Level 3 (lacking direct) evidence

In 2010, the estimated prevalence of dementia was 14.7% among adults aged more than 70 years in the United States (N Engl J Med. 2013;368[14]:1326-1334, Neuroepidemiology. 2007;29[1-2]:125-132). Oxidative stress and vascular impairment contribute to age-related cognitive decline, but no effective pharmacologic prevention or treatment strategies have been developed to date. 

Previously, the Prevención con Dieta Mediterránea (PREDIMED) trial showed that a Mediterranean diet supplemented with antioxidant-rich foods could reduce adverse cardiovascular outcomes in high-risk patients. A recent subgroup analysis of that trial examined cognitive function in 447 cognitively healthy adults (mean age, 67 years) who were randomly assigned to 1 of 2 antioxidant-enriched Mediterranean diets or a control diet (JAMA Intern Med. 2015;175(7):1094-1103). Patients were followed for a median of 4.1 years. The subjects were healthy adults (without cardiovascular disease at enrollment) with type 2 diabetes mellitus or 3 of 5 cardiovascular risk factors: smoking, hypertension, dyslipidemia, overweight or obesity, and family history of early-onset coronary heart disease. Participants were assigned to the Mediterranean diet plus extra-virgin olive oil (1 L/week), Mediterranean diet plus nuts (30g/day), or a control diet (advice to reduce dietary fat). They were assessed for cognitive function at baseline and at trial completion. Compared to the control diet, the Mediterranean diet plus extra-virgin olive oil was associated with greater improvements in the global cognition composite score (P < 0.01) and the frontal function composite score (P < 0.01), and the Mediterranean diet plus nuts was associated with a higher memory composite score (P < 0.05). In addition, all cognitive composite scores significantly decreased from baseline with the control diet.

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Statistically significant improvements in composite cognitive scores were observed for both Mediterranean diets, and results of this study are strengthened by the long duration of the intervention and wide array of neuropsychological tests used to evaluate cognitive functioning. However, the study is limited by the high loss to follow up, particularly in the control group, and relatively small number of participants receiving tests of frontal function and language. In addition, inclusion of only high vascular risk participants may affect the generalizability of the findings. Overall, the findings suggest that improvement in cognitive function in older adults may be an additional benefit beyond cardiovascular outcomes from a Mediterranean diet supplemented with antioxidant-rich foods. Whether these improvements in neuropsychological testing translate into real-world functional outcomes remains uncertain. 

Alan Ehrlich, MD, is a deputy editor for DynaMed, in Ipswich, Mass., and assistant clinical professor in Family Medicine, University of Massachusetts Medical School in Worcester.

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