• Posted June 13, 2025

Microbiome Linked To Memory Issues, Dementia In Parkinson's Patients

FRIDAY, June 13, 2025 (HealthDay News) — A person’s microbiome – the bacteria naturally living in the mouth and gut – might contribute to Parkinson’s disease, a new study says.

Specific changes in these bacteria are associated with cognitive decline in Parkinson’s, researchers reported June 9 in the journal Gut Microbes.

In particular, harmful bacteria moving from the mouth to the gut was tied to Parkinson’s patients shifting from mild memory issues to full-blown dementia, researchers found.

“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, but our findings suggest they may play an active role in worsening symptoms,” lead researcher Frederick Clasen, a research associate at the Quantitative Systems Biology Lab at King’s College London, said in a news release.

Parkinson’s is a brain disorder primarily associated with movement problems like shaking, stiffness and difficulty with balance and coordination.

But as the disease progresses, patients are more likely to develop memory problems as well, according to the National Institute on Aging.

“The human gut and oral bacterial communities are increasingly linked to neurodegenerative diseases,” senior researcher Saeed Shoaie, group leader of the Quantitative Systems Biology Lab at King’s College London, said in a news release.

“Disruptions in the gut-brain axis could trigger inflammation and immune responses that contribute to neuronal damage,” Shoaie added. “A common gum disease bacterium like Porphyromonas gingivalis has been discovered as a potential driver of Alzheimer’s.”

For the study, gut and mouth bacteria were analyzed among 114 people, including 41 Parkinson’s patients with mild cognitive impairment and 47 Parkinson’s patients with dementia.

Researchers discovered clear differences in the types and functions of bacteria between the groups.

In people with cognitive impairment, the gut contained more harmful bacteria – including many strains that likely migrated there from the mouth.

These bacteria were found to replace toxins that can damage gut tissue, promote inflammation and possibly affect the brain, researchers said.

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

The findings also show the importance of healthy lifestyle behaviors for people with Parkinson’s, like eating a good diet and maintaining oral hygiene, researchers said.

“As people with Parkinson’s become increasingly reliant on [caregivers], routine practices such as oral hygiene and nutritional intake may be neglected,” Shoaie said.

“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,” Shoaie added.

Future research will investigate how these bacteria and toxins might affect brain function, and whether lifestyle changes could help slow or prevent dementia in Parkinson’s patients, researchers said.

More information

The National Institute on Aging has more about Parkinson’s disease.

SOURCES: King’s College London, news release, June 9, 2025; Gut Microbes, June 9, 2025.