Mediterranean-Style Diet Associated With Increased Cortical Thickness

Deborah Brauser

August 15, 2016

More evidence suggests that eating a Mediterranean-style diet is linked not only to improved cognitive function but also to increased cortical thickness.

Assessment of 672 elderly participants in the Mayo Clinic Study of Aging showed that those with a higher Mediterranean diet (MedDiet) adherence score had significantly larger cortical thickness measurements in the frontal, parietal, and occipital lobes than did those with lower scores.

Those with a higher consumption of specifically fish or legumes also had larger cortical thickness, albeit in slightly different areas. On the other hand, those who consumed large amounts of carbohydrates and sugar had lower cortical thickness.

The study was published online July 25 in Alzheimer's & Dementia.

"Our study shows that diet impacts the structural changes in the brain that underlie the dementia syndrome," lead author Rosebud O. Roberts, professor of epidemiology and neurology at Mayo Clinic, Rochester, Minnesota, told Medscape Medical News.

Dr Rosebud O. Roberts

The results "can help people see that they have a role to play in reducing their risk of dementia by paying attention to their eating habits," added Dr Roberts.

In a separate publication, a new meta-analysis of 18 studies showed that high consumption of a MedDiet was associated with improved attention, memory, and language — as well as a "slowing down" of cognitive impairment.

First author of that report, Roy J. Hardman, PhD candidate, Center for Human Psychopharmacology at Swinburne University, Melbourne, Australia, told Medscape Medical News that what was surprising was the significant effects even when different measurement tools were used to assess diet adherence and various cognitive domains — "regardless of the population mix and the country in which the research was being conducted."

"The MedDiet is an example of healthy eating that can promote a healthy aging brain," he added.

The meta-analysis was published online July 22 in Frontiers in Nutrition.

MRI Evaluations

The original Mayo Clinic Study of Aging identified all residents of Olmstead County, Minnesota, who were aged 70 to 89 years on October 1, 2004.

For the current analysis, the researchers examined those who underwent MRI of all four lobes separately, averaged together (average lobar), and who were considered "cognitively normal" at the time of their MRI.

In this cohort, 52.5% were men and the mean age was 79.8 years. During a clinical evaluation, the participants were asked questions from the Functional Activities Questionnaire and Clinical Dementia Rating scale and underwent a battery of memory and neuropsychometric tests.

They also completed the Food Frequency Questionnaire (FFQ) regarding dietary patterns over the previous year. A MedDiet score was computed from these data.

Compared with a low score, a high MedDiet adherence score was associated with significantly greater cortical thickness in the following three lobes:

  • Frontal, P = .008

  • Parietal, P =.04

  • Occipital, P = .03

The average cortical thickness was also significantly larger (P = .01) among those with a higher adherence score.

Nonpharmacologic Intervention?

In addition, several individual regions of interest were greater in participants with high MedDiet scores, including the superior and middle temporal, precuneus, lingual, fusiform, and dorsolateral prefrontal cortex (range, P = .005 to .03).

Examination of individual components of a MedDiet showed that higher intake of legumes was significantly associated with greater occipital, parietal, precuneus, superior parietal, inferior parietal, and lingual thickness.

Fish intake was associated with greater thickness in the same areas except for the occipital and lingual, and with the addition of the posterior cingulate.

Increased cortical thickness was also found in certain brain regions of participants with higher consumption of whole grains or cereals and of total vegetables with and without legumes.

Negative associations with entorhinal cortical thickness were found with high intake of carbohydrates and sugary food; lower inferior and superior temporal thickness were associated with high intake of red meat.

This study "assessed associations of several dietary measures with MRI biomarkers of atrophy or neurodegeneration," write the investigators. "If validated prospectively, the associations will inform the development of nonpharmacologic interventions for maintaining cortical thickness and thereby reducing the risk of cognitive impairment."

Dr Roberts added that, all together, research has shown that poor eating habits can cause cardiovascular disease and cancer in midlife and cognitive impairment and dementia in late life.

So the takeaway message is that "clinicians should continue to educate their patients on the importance of maintaining a healthy diet not only for their heart, but also for their brain."

Dr Hardman, who wasn't involved with this research, called it a "great study" overall.

However, "the ramifications…have not been explored further, as the validation of this work and correlation with blood biomarkers still needs to be considered."

Still, he said that the study "is a valuable contribution to the substantiation" of how a MedDiet can benefit both an aging population and the general community.

Decreased AD Conversion

In the meta-analysis he was involved with, Dr Hardman and colleagues reviewed 18 longitudinal and prospective studies that examined dietary measures and cognitive improvements or impairment over the past 15 years.

Dr Roy J. Hardman

"It is important to consider that with the aging population, the burden to the health budget is not sustainable. And with the implementation of diet changes, the cognitive protective nature of the diet may prove to be substantial," he said.

The investigators found that 13 of the assessed studies showed improved cognitive function or a slowed rate of cognitive decline, which, in turn, minimized conversion to Alzheimer's disease in participants who had a strong adherence to a MedDiet.

"The specific cognitive domains that were found to benefit with improved Mediterranean Diet Score were memory (delayed recognition, long-term, and working memory), executive function, and visual constructs," they report.

There were no significant benefits for motor or action function from MedDiet adherence in studies that focused on those specific domains.

The researchers note that the overall results indicate "encouraging evidence" of a link between consumption of this type of diet and cognitive improvement.

However, they also stress the need for a computer-based FFQ for obtaining a standardized MedDiet score and that future randomized, controlled trials should use validated cognitive evaluations "that are sensitive to cognitive faculties, which are compromised with age and potentially amenable to interventions."

Research now shows that "the MedDiet offers the opportunity to change some modifiable risk factors," Dr Hardman stated in a press release.

"These include reducing inflammatory responses, increasing micronutrients, improving vitamin and mineral imbalances, changing lipid profiles…and maybe changing the gut micro-biota."

The first study was funded by grants from the National Institutes of Health (NIH) and by the Mayo Foundation for Medical Education and Research. Dr Roberts reports receiving research funding from the NIH. Disclosures for the coauthors are in the original paper. The authors of the meta-analysis have disclosed no relevant financial relationships.

Alzheimers Dement. Published online July 25, 2016. Abstract

Front Nutr. Published online July 22, 2016. Full article

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