New Study Links Gut Health to Cognitive Loss in Parkinson’s

Cognitive decline in Parkinson's disease has been linked to changes in gut microorganisms, also known as the microbiome. This includes the progression from mild memory issues to dementia, a common and distressing symptom of the disease.

These microbiome changes could act as early warning signs. They may help doctors detect and treat Parkinson’s before symptoms become more severe. Currently, the disease is difficult to diagnose in its early stages because symptoms develop slowly.

The study, led by King's College London, adds to evidence showing a strong connection between gut and brain health. Although the ‘gut-brain’ link has been widely studied, few investigations have focused on how the gut may affect cognitive decline in conditions like Parkinson’s.

The human gut and oral bacterial communities are increasingly linked to neurodegenerative diseases. Disruptions in the gut-brain axis could trigger inflammation and immune responses that contribute to neuronal damage. A common gum disease bacterium, like Porphyromonas gingivalis, has been discovered as a potential driver of Alzheimer’s.

Dr. Saeed Shoaie, Study Co-Author and Leader, Quantitative Systems Biology Lab, King’s College London

The study, published in Gut Microbes, examined gut and mouth bacteria using 228 stool and saliva samples. It included two groups of people with Parkinson’s: those with moderate cognitive decline and those with dementia, at various disease stages. A healthy control group without Parkinson’s was also included.

Researchers found clear differences in the types and functions of bacteria across the groups. In people with cognitive impairment, the gut contained more harmful bacteria, many of which likely came from the mouth.

This process is known as "oral-gut translocation." It involves oral bacteria entering the gut, where they are not normally found. These bacteria were found to produce virulence factors—chemicals that can damage gut tissue, cause inflammation, and possibly affect the brain.

We do not 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. But our findings suggest they may play an active role in worsening symptoms.

Dr. Frederick Clasen, Study First Author and Research Associate, Quantitative Systems Biology Lab, King’s College London

The researchers used artificial intelligence to link these toxins to cognitive decline in people with Parkinson’s. AI helped identify specific bacterial species and functions that traditional methods might have missed.

Dr. Clasen elaborated, “These toxins could be used as biological markers to identify patients at higher risk of dementia in Parkinson’s. In the future, they might also be targets for new treatments that protect the brain by changing the gut environment.”

The results also highlight the importance of good dental hygiene and diet for people with Parkinson’s, especially as the disease progresses.

Dr. Shoaie added, “The emerging evidence underscores the potential importance of maintaining oral and gut health in mitigating or slowing neurodegenerative processes. As people with Parkinson’s become increasingly reliant on carers, routine practices such as oral hygiene and nutritional intake may be neglected. Our findings suggest that promoting a healthy microbiome through consistent oral care, a balanced diet, and potentially targeted probiotic interventions could support improved disease management in Parkinson’s.”

Future research will explore whether these bacteria and their toxins directly affect brain function. It will also examine whether changing the microbiome through diet, dental care, or medication can help reduce or prevent dementia in people with Parkinson’s.