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

In a groundbreaking study published in the journal *Gut Microbes* on June 8, 2025, researchers at King’s College London have revealed a significant connection between gut bacteria and the early stages of cognitive decline in Parkinson’s disease patients. The findings suggest that changes in the composition of oral and gut bacteria may serve as early warning signs of symptom progression in individuals suffering from this neurodegenerative condition.

Parkinson’s disease, which affects approximately 1% of the global population over the age of 60, is characterized by motor symptoms such as tremors and stiffness, as well as non-motor symptoms including cognitive decline and mood disorders. According to the Alzheimer’s Society, about one-third of individuals with Parkinson’s eventually develop dementia, underscoring the urgency of understanding the disease’s progression.

The study, led by Dr. Saeed Shoaie, a group leader at the Quantitative Systems Biology lab at King’s College London, involved the analysis of 228 saliva and stool samples collected from three groups: 41 patients with Parkinson’s and mild cognitive impairment, 47 patients with Parkinson’s and dementia, and 26 healthy control subjects. The researchers discovered that those with mild cognitive impairment exhibited elevated levels of harmful bacteria, many of which are typically found in the mouth. This bacterial imbalance releases toxins that could potentially damage gut tissue, promote inflammation, and negatively impact brain function.

Dr. Shoaie emphasized the emerging link between gut microbiota and neurodegenerative diseases. He stated, “Disruptions in the gut-brain axis could trigger inflammation and immune responses that contribute to neuronal damage.” Notably, the common gum disease bacterium *Porphyromonas gingivalis* has been identified as a potential contributor to Alzheimer’s disease, further reinforcing the importance of gut and oral health in mitigating neurodegenerative processes.

For this study, the researchers employed artificial intelligence to identify bacterial species and functions that traditional testing methods might overlook. This innovative approach allowed them to establish a more precise correlation between specific bacterial toxins and cognitive decline in Parkinson’s patients. Dr. Frederick Clasen, a research associate at the QTS lab, stated, “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. However, our findings suggest they may play an active role in worsening symptoms.”

The implications of this research are substantial. By identifying these microbial changes, healthcare providers may one day have biological markers to assess the risk of dementia among Parkinson’s patients. Furthermore, these findings could pave the way for targeted treatments aimed at altering the gut microbiome to protect brain health.

Dr. Shoaie concluded by highlighting the necessity of maintaining oral and gut health in managing Parkinson’s disease. As patients often become reliant on caregivers, routine oral hygiene and nutritional practices may be neglected. He suggested that promoting a healthy microbiome through consistent oral care, a balanced diet, and potential probiotic interventions could enhance disease management for individuals with Parkinson’s.

As the medical community continues to explore the intricacies of Parkinson’s disease, this study signifies a promising step toward understanding the interplay between gut health and cognitive function, potentially leading to innovative strategies for treatment and prevention in the future.