Can Bacteria in the Mouth Predict Cognitive Decline in People with Parkinson's Disease? Study Finds Out

New Delhi: A new study published in Gut Microbes by researchers at King's College London has uncovered a connection between oral and gut bacteria and the progression of cognitive decline in people with Parkinson’s disease. The findings suggest that specific changes in the microbiome-he community of bacteria in the body—may serve as early warning signs of dementia, a common and distressing symptom in Parkinson’s disease.

Parkinson’s disease is notoriously difficult to diagnose in its early stages, as symptoms like memory issues and movement problems develop slowly over time.

Led by Dr. Saeed Shoaie, group leader of the Quantitative Systems Biology Lab at King’s College London, the study analysed 228 stool and saliva samples from individuals at different stages of Parkinson’s. These included patients with mild cognitive impairment, patients with dementia, and a control group without Parkinson’s. “The human gut and oral bacterial communities are increasingly linked to neurodegenerative diseases,” Dr. Shoaie noted. “Disruptions in the gut-brain axis could trigger inflammation and immune responses that contribute to neuronal damage.”

Researchers found clear differences in bacterial composition between groups. Notably, harmful oral bacteria, such as Porphyromonas gingivalis, had migrated to the gut, a process known as “oral-gut translocation.” These bacteria release virulence factors, or toxins, that damage gut tissue and may contribute to brain inflammation.

“We don’t yet know if the bacteria are causing the cognitive decline or if changes in the body due to Parkinson’s allow these bacteria to grow,” said first author Dr. Frederick Clasen. “But our findings suggest they may play an active role in worsening symptoms.”

Using artificial intelligence, the team identified specific bacterial species and toxins linked to cognitive decline. These may eventually serve as biomarkers to predict dementia risk or targets for new treatments.

The study also emphasises the importance of oral hygiene and a healthy diet in people with Parkinson’s. As Dr. Shoaie concluded, “Promoting a healthy microbiome through consistent oral care, a balanced diet, and potentially targeted probiotic interventions could support improved disease management in Parkinson’s.”

Reference: Clasen, F., Yildirim, S., Arıkan, M., Garcia-Guevara, F., Hanoğlu, L., Yılmaz, N. H., … Shoaie, S. (2025). Microbiome signatures of virulence in the oral-gut-brain axis influence Parkinson’s disease and cognitive decline pathophysiology. Gut Microbes, 17(1). https://doi.org/10.1080/19490976.2025.2506843