GW Research Suggests Gut Bacteria May Link to Memory Decline in Alzheimer’s Disease

New research published Jan. 22 in Alzheimer's & Dementia: The Journal of the Alzheimer's Association contributes to growing evidence that imbalances in the gut microbiome, known as dysbiosis, may play a key role in the development and progression of mild cognitive impairment (MCI) and Alzheimer's disease. Alzheimer's affects an estimated 6.7 million individuals in the United States and nearly 50 million worldwide.

Researchers are working to understand the biological processes leading to memory loss and cognitive decline. One area they're studying is the microbiota-gut-brain axis-the communication system between the gut, the immune system and the brain. Research suggests that this system may contribute to brain inflammation and damage to nerve cells, which could play a role in Alzheimer's disease.

"Microbial signatures offer an important starting point for understanding how gut health may influence neuroinflammation and cognitive decline," said lead researcher Leigh Frame, associate professor in the George Washington University School of Medicine and Health Sciences.

The GW team analyzed 58 human studies published through February 2023 across different countries, making this the most thorough review to date focused exclusively on human studies. This is important because studies of animal models in this area do not typically translate well to human beings.

Across studies, individuals with MCI and Alzheimer's disease consistently showed different gut bacteria compared to older adults without cognitive decline.

Key findings of the GW review include:

• People with Alzheimer's disease tend to have higher levels of certain groups of gut bacteria-particularly the phyla Pseudomonadotaand Actinomycetota.

• Some people with Alzheimer's disease have lower microbial diversityin their gut-meaning they have fewer types of bacteria than usual.

• The types and amounts of gut bacteria are different in people with mild cognitive impairment, Alzheimer's disease, and healthy individuals. This suggests different microbiome signatures at different stages of cognitive decline.

• In people with Alzheimer's disease, functional changes in gut bacteria were also observed, including reduced activity in pathways linked to energy production and immune function.

Although the review does not establish cause and effect, the findings align with broader evidence suggesting that diets rich in fiber may support a healthier gut microbiome, which could have downstream implications for inflammation and brain health.

"While these early, largely observational results are encouraging, we need clinical trials to determine whether microbiome-targeted interventions can meaningfully alter disease trajectories," Frame said. "These trials are already underway in our lab and labs around the world."