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Reference: JAMA Intern Med 2015 May 11 early online (level 3 [lacking direct] evidence)
In 2010, the estimated prevalence of dementia was 14.7% among adults over 70 years old in the United States (N Engl J Med. 2013 Apr 4;368(14):1326, Neuroepidemiology. 2007;29(1-2):125). Oxidative stress and vascular impairment contribute to age-related cognitive decline, but no effective pharmacological prevention or treatment strategies have been developed to date (Biochem Pharmacol. 2014 Apr 15;88(4):631, Br J Psychiatry. 2013Sep;203(3):255). Previously, the 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 randomized to 1 of 2 antioxidant-enriched Mediterranean diets or a control diet. Patients were followed for median 4.1 years.
The study included healthy adults (without cardiovascular disease at enrollment) with type 2 diabetes mellitus or 3 of 5 cardiovascular risk factors including smoking, hypertension, dyslipidemia, overweight or obesity, and family history of early-onset coronary heart disease. Participants were assigned to Mediterranean diet plus extra-virgin olive oil (1 L/week) vs. Mediterranean diet plus nuts (30g/day) vs. control diet (advice to reduce dietary fat), and were assessed for cognitive function at baseline and at trial completion. Compared to control diet, Mediterranean diet plus extra-virgin olive oil 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 control diet.
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.
For more information, see the Mediterranean diet topic in DynaMed.