Fig. 3

Altered phylum- and genus-level taxonomies in participants with cognitive impairment. a The circular layout illustrates the mean relative abundance of phyla (16S rRNA gene sequencing) among the mild, questionable, and normal groups in the GNHS. Colors in upper and lower halves of the outermost circle represent different groups of participants and microbial phyla, respectively. Width of each track highlights mean relative abundance of each phylum contained in different groups of participants. b and c The relative abundance of Firmicutes and Bacteroidetes (b), and the ratio of Bacteroidetes to Firmicutes (c) among the GNHS participants with different degrees of cognitive impairment are presented by the violin plot with included boxplot. The boxplots show median and interquartile ranges (IQR). Whiskers specify ± 1.5 × IQR. (ns, P > 0.05; *0.005 < P < 0.05; **P < 0.005; two-sided Mann–Whitney U test). d Key gut microbial genera that contribute to distinguishing participants with different levels of cognitive impairment (Mild vs. Normal in the GNHS; AD vs. NC in the AD case–control study) using LASSO models. The bars are colored according to the direction of association between the genera and cognitive impairment (orange for positive correlation [harmful]; dark green for negative correlation [beneficial]). ^#Key genera selected in both populations. e Validation of the relationships between key genera and cognitive performance using linear mixed-effect models in the CHNS. The forest plot shows the result of the association between Bacteroides and global cognitive scores. The completed result is provided in the Additional file 1: Table S6. In the GNHS, participants were classified into corresponding degrees of cognitive impairment according to their MMSE scores: ‘Mild’ (score ≤ 25), ‘Questionable’ (score 26–29) and ‘Normal’ (score 30). In the CHNS, the participants were classified into T1, T2 and T3 groups according to the tertiles of their global cognitive scores. GNHS Guangzhou Nutrition and Health Study, AD Alzheimer’s disease, LASSO least absolute shrinkage and selection operator, CHNS China Health and Nutrition Survey, T tertile