Recently, an association between dysbiosis of the gut microbiota (GMB) and the development of several diseases, such as Alzheimer’s disease (AD), has been proposed. Dysbiosis involves changes in microbial diversity influenced by environmental factors, like diet or lifestyle. In this study, we investigated the role of GMB parameters in Spanish AD patients, assessing the impact of adherence to the Mediterranean lifestyle (ML), as well as to characterize these parameters in relation to neuropsychological, neuropsychiatric, emotional, and functionality parameters. A case–control study was conducted to investigate the association between the composition of the GMB and cognitive, emotional, neuropsychiatric, and functionality status in Spanish AD patients, along with a shotgun metagenomics approach. Richness and alpha-diversity were significantly lower in the AD group compared to the controls. PERMANOVA and ANOSIM tests of Bray–Curtis dissimilarity, Aitchison distance, and Jaccard similarity did not showed significant differences in beta-diversity between the two groups. Moreover, associations between various phyla of the AD group and orientation performance, food consumption, and activities of daily living were identified. Dysbiosis observed in Spanish AD patients is characterized by reductions in richness and alpha-diversity, alongside alterations in GMB composition, which may be linked to adherence to the ML and cognitive and functionality symptoms.

Parkinson's disease (PD) and dementia with Lewy bodies (DLB) are related α-synucleinopathies that share Lewy pathology, but they differ clinically. Increasing evidence links gut microbiota (GMB) dysbiosis and microbially derived metabolites to Parkinsonian disorders yet reported associations remain heterogeneous across cohorts and the Lewy body dementia syndromes are comparatively under characterized. This study integrated clinical characterization and GMB profiling in Parkinson's disease dementia (PDD), DLB, and healthy controls (HC) to identify shared and syndrome specific features, and to relate these patterns to cognitive, neuropsychiatric, and functional outcomes. The present cross-sectional case-control study in Spain included 76 adults aged 60 to 85 years (HC = 38, PDD = 27, DLB = 11). Stool samples underwent shotgun metagenomic sequencing, with species-level taxonomic profiling using Kraken2. Community diversity was assessed using observed species and Chao1 richness, Shannon alpha diversity, and Bray-Curtis dissimilarity for beta diversity. LEfSe and multivariate linear modeling with MaAsLin2 were performed to identify GMB species associated with PDD and DLB and their clinical correlates. PDD showed higher richness compared with HC. Shannon alpha diversity did not differ between groups. Bray-Curtis differed by separation of HC from both PDD and DLB, with no significant difference between Lewy body dementia syndromes. LEfSe identified 19 significantly differential taxa. Furthermore, several taxa showed significant multivariable associations with clinical outcomes. PDD and DLB shared a broadly similar GMB alteration away from HC, with multivariable associations between several taxa and clinical outcomes. Longitudinal and functional studies are needed to clarify causality and biomarker potential.

This article presents data collected from a total of 50 older adults (25 healthy controls and 25 diagnosed with Alzheimer's disease). Among the assessments performed in this sample was a comprehensive neurocognitive screening: including working memory, cognitive flexibility, perception, attention, motor coordination, inhibitory control, verbal fluency and visuo-spatial skills. The data presented also include analysis of the participants' gut microbiota using the shot gun approach in faecal samples. Finally, evaluations of the emotional state, level of functioning and adherence to the Mediterranean lifestyle of all participants are also available. Despite the limited sample size due to challenges in patient recruitment, present data could be useful in the identification of microbial signatures potentially predictive of cognitive decline or AD progression and also for helping to the design of clinical trials targeting the microbiome to assess effects on cognitive function. Furthermore, it is well known that the gut microbiota exhibits significant variability associated with lifestyle habits, diet, and geographic location, underscoring the critical influence of environmental and cultural factors in shaping its composition. These data are of utmost importance when considering regional and lifestyle-related diversity in microbiome research, as they can help researchers explore personalized therapeutic approaches and enhance participant stratification in future clinical trials.