Gut Bacteria and Dementia Linked.

HONOLULU — Depletion of certain gut bacteria, and an elevated level of other bacteria, are associated with an increased risk for dementia, a new study suggests.

“Although our study has numerous limitations, the results suggest that the gut microbiome could be a new target for the management of dementia,” study author Naoki Saji, MD, PhD, Vice Director, Center for Comprehensive Care and Research on Memory Disorders, National Center for Geriatrics and Gerontology in Japan, told Medscape Medical News.

Doctors should urge patients to “take care of their gut,” said Saji.
The study was presented here at the International Stroke Conference (ISC) 2019, and published online January 30 in Scientific Reports.

The gut microbiome refers to microorganisms that live in the digestive tract; there are about a thousand different species of bacteria, comprising trillions of cells. Recent research has correlated certain changes in gut bacteria with inflammatory and autoimmune conditions, and studies have shown that changes in diet can alter gut bacteria.

The gut microbiome has become a hot topic for many experts, including Saji. His research interests include associations between dementia and cerebrovascular and cardiovascular diseases. He supports the hypothesis that these diseases share common risk factors.
Results of previous research suggest a relationship between the gut microbiome and cardiovascular diseases. “I thought that a relationship between dementia and gut microbiome might be also possible,” said Saji.
The new study included 128 outpatients visiting a memory clinic at their institution; participants had a mean age of 74.2 years and 59% were female.

Researchers collected information on demographics, risk factors, and activities of daily living, and assessed cognitive function using neuropsychological tests and brain MRI scans.
As well, from fecal samples, they determined gut microbiota using terminal restriction fragment length polymorphism (T-RFLP) analysis. This, said Saji, is a well-established and reliable method of classifying gut microbiota.
Investigators divided study participants into demented and nondemented groups. They used multivariable logistic regression models to identify factors independently associated with dementia.
Silent lacunar infarcts and cerebral microbleeds were more frequently seen on MRI scans of patients with dementia, the researchers report.
Decreased Bacteroides

The T-RFLP analysis revealed group differences in components of gut microbiota. For example, levels of Bacteroides (enterotype I), which are organisms that normally live in the intestines and can be beneficial, were decreased in demented compared with nondemented patients.
Other bacteria (enterotype III) were increased in the group with dementia.
Multivariable analyses showed that enterotype I (odds ratio [OR] 0.1, 95% confidence interval [CI] 0.02 – 0.4, P < .001) and enterotype III (OR 12.7, 95% CI 3.3 - 65.8, P < .001) were strongly associated with dementia, independent of traditional dementia biomarkers such as APOE ?4 genetic status; deficits in certain neurochemicals; and high scores on Voxel-Based Specific Regional Analysis System for Alzheimer's Disease (VSRAD). Fecal concentrations of ammonia, indole, skatole, and phenol were higher in demented compared with nondemented patients.

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