Changes in gut bacteria could be linked to Alzheimer’s disease, according to a new study from the University of Wisconsin School of Medicine and Public Health.

The study, “Gut microbiome alterations in Alzheimer’s disease” was published today in Scientific Reports.

Dr. Barbara Bendlin, associate professor of medicine (geriatrics) at UW, led the study with Dr. Federico Rey, assistant professor of bacteriology. Nicholas Vogt, an MD-PhD student in Bendlin’s lab, is the first author on the paper.

“The results imply that gut bacteria may play a role in risk for dementia due to Alzheimer’s disease,” said Bendlin.

While previous animal studies had indicated that gut microbes might play a role in the accumulation of amyloid plaques (a hallmark feature of Alzheimer’s disease), the relationship between gut microbial communities and Alzheimer’s disease in humans was unknown.

To address this, microbiome and Alzheimer’s disease researchers at UW-Madison teamed up to analyze fecal samples collected from 25 human volunteers with mild to moderate dementia due to Alzheimer’s disease and 25 human volunteers who were cognitively healthy. The two groups were of similar age, sex, ethnicity, weight, and diabetes status.

“By using DNA sequencing to take a ‘snapshot’ of gut bacterial composition, we found that individuals with dementia had decreased microbial richness and diversity in their gut microbiome compared to people without a diagnosis of dementia” said Vogt.

“We were able to identify broad taxonomical changes in gut bacterial composition, as well as changes in abundance of a number of bacterial groups, some of which were more abundant in people with dementia due to Alzheimer’s disease and some of which were less abundant,” said Vogt.

The researchers also found that the altered abundance of these bacterial groups was associated with the hallmark pathologies of Alzheimer’s disease as shown by cerebrospinal fluid samples taken from participants.

“A profile of gut bacteria that looked more similar to what we observed in dementia was associated with Alzheimer’s disease pathology in the brain,” said Bendlin. “This was even the case among people who were cognitively healthy, suggesting a link between gut bacteria and the brain even in the absence of dementia.”

The work supports an emerging idea of ongoing communication between the brain and microbes in the gut.

“Microbes play key roles in processes in the body like metabolism and immune responses. We are only beginning to appreciate that alterations in the structure and functions of gut microbial communities can contribute to development of disease in the brain,” said Rey.

The researchers plan to conduct further studies to investigate how changes in the composition of gut bacteria could initiate or worsen processes that affect the progression of Alzheimer’s disease.

Additional authors are Robert Kerby, Kimberly Dill-McFarland, Sandra Harding, Andrew Merluzzi, Sterling Johnson, Cynthia Carlsson, Sanjay Asthana, Henrik Zetterberg, and Kaj Blennow.