Gut microbiome diversity and brain volume among general japanese men

Objective: Accumulative evidence links gut microbiome diversity to the central nervous system, cognition, and mental disorders. However, little is known regarding the associations of gut microbiome diversity with brain volumes in human. We assessed the association of within-person gut microbiome diversity and brain volumes in general Japanese men. Methods: Healthy Japanese men (n = 623) aged 40–79 years participated in the examination of the Shiga Epidemiological Study of Subclinical Atherosclerosis II (SESSA II) between 2010 and 2015. They underwent assessments of gut microbiota diversity (Shannon Diversity Index and Chao Index) through 16S rRNA sequencing using DNA extracted from stool samples and brain volumes in milliliters (i.e., total brain volume, white matter, gray matter, and hippocampus) and white matter lesion volumes (WMLV, reflecting cerebral small vessel disease) via brain magnetic resonance imaging (MRI). Multivariable linear regression tested the effect of indexes per SD on the outcomes. Results: In unadjusted models, higher Shannon Index and Chao Index were associated with lower volumes in hippocampus (see table). After adjustments for age and total intracranial volume, higher Shannon Index and Chao Index showed associations with higher volumes in gray matter but were attenuated after additional adjustments for body mass index, physical activity, smoking, drinking, and hypertension. Conclusions: Among general Japanese men, higher within-person gut microbiota diversity was not associated with volumes in total brain volume, white matter, gray matter, hippocampus, and WMLV. Further studies are warranted to identify specific gut microbiome signatures associated with brain volumes in human.