Mediterranean Diet and Magnetic Resonance Imaging-Assessed Brain Atrophy in Cognitively Normal Individuals at Risk for Alzheimer's Disease

Abstract

Objectives: Epidemiological evidence linking diet, one of the most important modifiable environmental factors, and risk of Alzheimer's disease (AD) is rapidly increasing. Several studies have shown that higher adherence to a Mediterranean diet (MeDi) is associated with reduced risk of AD. This study examines the associations between high vs. lower adherence to a MeDi and structural MRI-based brain atrophy in key regions for AD in cognitively normal (NL) individuals with and without risk factors for AD.

Design: Cross-sectional study.

Setting: Manhattan (broader area).

Participants: Fifty-two NL individuals (age 54+12 y, 70% women) with complete dietary information and cross-sectional, 3D T1-weighted MRI scans were examined.

Measurements: Subjects were dichotomized into those showing higher vs. lower adherences to the MeDi using published protocols. Estimates of cortical thickness for entorhinal cortex (EC), inferior parietal lobe, middle temporal gyrus, orbitofrontal cortex (OFC) and posterior cingulate cortex (PCC) were obtained by use of automated segmentation tools (FreeSurfer). Multivariate general linear models and linear regressions assessed the associations of MeDi with MRI measures.

Results: Of the 52 participants, 20 (39%) showed higher MeDi adherence (MeDi+) and 32 (61%) showed lower adherence (MeDi-). Groups were comparable for clinical, neuropsychological measures, presence of a family history of AD (FH), and frequency of Apolipoprotein E (APOE) ε4 genotype. With and without controlling for age and total intracranial volume, MeDi+ subjects showed greater thickness of AD-vulnerable ROIs as compared to MeDi- subjects (Wilk's Lambda p=0.026). Group differences were most pronounced in OFC (p=0.001), EC (p=0.03) and PCC (p=0.04) of the left hemisphere. Adjusting for gender, education, FH, APOE status, BMI, insulin resistance scores and presence of hypertension did not attenuate the relationship.

Conclusion: NL individuals showing lower adherence to the MeDi had cortical thinning in the same brain regions as clinical AD patients compared to those showing higher adherence. These data indicate that the MeDi may have a protective effect against tissue loss, and suggest that dietary interventions may play a role in the prevention of AD.

Keywords: Alzheimer's disease; Mediterranean diet; brain imaging; diet; early detection; magnetic resonance imaging (MRI).

Figure 1

Three-dimensional representations of the 5 ROIs examined in the current study (only right hemisphere is shown). All of the ROIs are visible in the lateral (top) and medial (bottom) views of the gray matter surface

Figure 2

Mediterranean diet and APOE genotype interactions on regional MRI thickness Abbreviations: MeDi = Mediterranean diet group (MeDi- = lower adherence vs MeDi+ = higher adherence), APOE4 = Apolipoprotein E ε4 allele (APOE4- = non carriers, APOE4+ = carriers). MRI measures are age and total intracranial volume-adjusted residuals

Figure 3

Associations between Mediterranean diet scores and regional MRI thickness MRI measures are age and total intracranial volume-adjusted residuals

Figure 4

MRI scans of two representative NL cases showing higher vs. lower adherence to the MeDi. Participants were 52 and 50 year old, respectively, with MMSE>28, education>12 y, normal cognitive test performance by age and education. The MeDi+ subject shows no ventricular enlargement or hippocampal atrophy by age. The MeDi- subject shows mild ventricular enlargement, hippocampal and temporal cortex atrophy by age (arrows)