Mediterranean diet linked to lower dementia risk, finds extensive review

In a recent study published in the journal Aging Clinical and Experimental Research, researchers evaluated the link between the Mediterranean diet (MedDiet) and reduced dementia risk in older adults through a systematic review and meta-analysis.

Study: Association between Mediterranean diet and dementia and Alzheimer disease: a systematic review with meta-analysis. Image Credit: luigi giordano

Background 

Dementia, a cluster of brain disorders impairing cognitive functions, predominantly impacts older adults, with projections indicating that nearly 14 million will be affected by 2060. Alzheimer’s disease (AD), the most common form, results from the buildup of amyloid-beta peptides (Aβ). Risk factors span from genetics to lifestyle choices, yet measures like higher education and a healthy diet, particularly the MedDiet, could offer protective benefits. This diet emphasizes fruits, vegetables, and olive oil, but research on its efficacy against dementia has shown mixed outcomes. Consequently, further research is required to resolve these inconsistencies and understand how such dietary patterns might reduce dementia risks across different groups.

About the study 

The present systematic review and meta-analysis followed Cochrane Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 (PRISMA-2020) and Meta-analysis Of Observational Studies in Epidemiology (MOOSE) guidelines, utilizing a detailed protocol registered under International Prospective Register of Systematic Reviews (PROSPERO) CRD 42023444368. The study, executed through comprehensive searches on PubMed/MEDLINE and Scopus on July 17, 2023, rigorously examined the intersection of MedDiet, aging, and dementia outcomes.

The inclusion criteria, centered on observational studies of the older adults examining MedDiet’s impact on dementia, facilitated the extraction of relevant studies while excluding non-original, non-English, or unrelated dietary studies. Independent reviewers scrutinized the selected studies through a two-tiered screening process. Data was carefully extracted into a pre-tested Excel sheet, capturing a comprehensive range of study details, from design to dietary assessment tools, ensuring a robust analysis.

Quality was rigorously assessed using the Newcastle–Ottawa Scale (NOS), setting a high-quality benchmark at seven or more points. Statistical analysis, adhering to PRISMA 2020’s transparency in documenting selection processes, combined effect sizes from diverse study designs to assess MedDiet’s impact on dementia risk. Heterogeneity and publication bias were thoroughly evaluated, with adjustments made for detected biases. Sensitivity and subgroup analyses further refined the understanding of this diet-dementia relationship, focusing on dementia types, study quality, and methodologies.

Study results 

In the present study, a total of 682 records were unearthed, leading to a refined pool of 21 studies for inclusion after thorough screening and assessment processes. This selection journey, marked by rigorous criteria and methodological rigor, shed light on the diverse global research efforts spanning continents from Europe to Australia, capturing studies as early as 1970 through to 2022. The studies employed a variety of designs, predominantly cohort and cross-sectional studies, with sample sizes ranging significantly. Notably, the assessment of dietary adherence utilized a range of MedDiet scores, reflecting the methodological diversity in capturing diet-dementia associations.

The demographic makeup of the study populations primarily consisted of community-dwelling elderly individuals, though some studies focused on specific groups such as Medicare beneficiaries or residents of healthcare institutions. The gender representation was broadly inclusive, although a few studies targeted postmenopausal women or men exclusively. High-quality scores were attributed to all studies included in the meta-analysis, underscoring the credibility and robustness of the findings presented.

Central to this review, the meta-analysis illuminated a moderate reduction in dementia risk associated with higher adherence to the MedDiet despite moderate to high statistical heterogeneity among the datasets. This finding was refined by various sensitivity and subgroup analyses, which dissected the data by dementia type, study design, and geographical regions, among other factors. Each analysis contributed layers of understanding to the complex relationship between diet and dementia, reinforcing MedDiet’s potential as a modifiable risk factor in dementia prevention.

Particularly compelling was the pooled analysis for AD, which showcased a more pronounced protective effect of MedDiet against this specific form of dementia. However, the study also acknowledged the presence of potential publication bias, necessitating a cautious interpretation of the results. Despite these challenges, the consistency of findings across different analyses underscores MedDiet’s relevance in dementia risk reduction strategies.

Conclusions 

To summarize, this systematic review and meta-analysis explored the link between MedDiet and reduced dementia risk among older adults, finding an 11% decrease in risk among those with high adherence. Particularly notable was the 27% risk reduction for AD, although the association with mild cognitive impairment (MCI) was not significant. Furthermore, the study addressed statistical heterogeneity and methodological diversity in MedDiet scoring, enhancing the robustness of its findings.