New Research Links Oral and Gut Bacteria to Cognitive Decline in Parkinson's Disease

Scientists have uncovered a significant connection between bacteria present in the mouth and gut and the progression of cognitive decline in Parkinson's disease. Variations in the microbiome— the collection of microorganisms residing in these areas—have been associated with the severity of cognitive impairment, including shifts from mild memory issues to dementia, which is a common and challenging symptom of Parkinson's.

These microbiome changes could serve as early indicators of Parkinson's, potentially allowing for earlier detection and intervention before symptoms worsen. Since initial symptoms often develop gradually, identifying such biomarkers is crucial for timely diagnosis.

Research led by King's College London emphasizes the close relationship between the gut, oral health, and brain function. While this 'gut-brain' axis has been extensively studied, little is known about the gut's role in the cognitive deterioration seen in neurodegenerative diseases like Parkinson's.

Dr. Saeed Shoaie, head of the Quantitative Systems Biology Lab at King's College London, explained that disruptions in the microbial communities within the gut and mouth may trigger inflammatory and immune responses that contribute to neuronal damage. Notably, bacteria linked to common gum disease, such as Porphyromonas gingivalis, have been implicated as potential factors in Alzheimer's disease.

In a recent study published in Gut Microbes, scientists analyzed 228 stool and saliva samples from Parkinson's patients at different stages—those with mild cognitive decline and those with dementia—alongside healthy controls. They identified distinct differences in bacterial types and functions, notably an increase in harmful bacteria originating from the mouth, which invade the gut—a process termed 'oral-gut translocation.' These bacteria generate virulence factors—molecules that damage gut tissue and promote inflammation—that could influence brain health.

First author Dr. Frederick Clasen highlighted that it remains unclear whether these bacteria cause cognitive decline or if Parkinson's-related changes in the body foster bacterial growth. Nonetheless, using artificial intelligence, the team linked these bacterial toxins to cognitive deterioration, suggesting they could serve as biomarkers and treatment targets.

The research underscores the importance of maintaining oral and gut hygiene, along with balanced nutrition, especially as Parkinson's progresses. Dr. Shoaie emphasized that preserving a healthy microbiome through oral care and diet might help mitigate or slow neurodegenerative processes. Future studies aim to determine whether altering the microbiome could directly impact brain health and reduce dementia risk in Parkinson's patients.

Source: https://medicalxpress.com/news/2025-06-mouth-gut-bacteria-linked-brain.html