A new study out of King’s College London is casting a fresh spotlight on an often-overlooked culprit in Parkinson’s disease progression: the bacteria living quietly in our mouths and intestines.
While Parkinson’s is traditionally defined by its motor symptoms—tremors, stiffness, balance issues—the disease’s impact on cognition has drawn increasing concern. Now, researchers suggest that the microbiome, the community of microbes inhabiting the human body, might be a more active player in that cognitive deterioration than previously thought.
Dr. Frederick Clasen, a research associate in the Quantitative Systems Biology Lab at King’s, led a team that explored how specific microbial shifts in the gut and mouth might relate to dementia in Parkinson’s patients. The team’s findings, published June 9 in Gut Microbes, paint a provocative picture.
The study followed 114 individuals, all living with Parkinson’s. Among them, 41 had mild cognitive impairment and 47 had already progressed to dementia. When the researchers analyzed their microbiomes, they noticed something striking: in those with more advanced cognitive symptoms, the gut was populated with a greater number of harmful bacteria typically found in the mouth.
“It’s not yet clear whether these bacteria are passengers or drivers in the disease process,” said Clasen. “But their presence correlates with worsening memory and cognitive performance. That gives us reason to look much more closely.”
What makes this discovery especially intriguing is that these oral invaders weren’t just present—they appeared to be actively producing toxins capable of damaging the gut lining, stirring inflammation, and possibly sending distress signals along the gut-brain axis. The same biological pathway has been previously implicated in Alzheimer’s disease, especially in cases where gum disease pathogens like Porphyromonas gingivalis have been found near brain tissue.
Dr. Saeed Shoaie, senior author of the study and head of the Quantitative Systems Biology Lab, emphasized the significance of this microbial migration. “We know the gut and brain are in constant biochemical conversation,” Shoaie noted. “Disruptions in this dialogue, possibly driven by oral pathogens taking up residence where they shouldn’t, could be influencing how neurodegeneration unfolds.”
The implications ripple out beyond biology into caregiving. Many individuals with Parkinson’s, especially in later stages, rely heavily on caregivers. As such, basic routines—oral hygiene, healthy eating—can become inconsistent or overlooked.
“Our results highlight how vital it is to maintain oral health and gut health throughout the disease,” Shoaie said. “It’s not just about preventing cavities or indigestion. These routines might be safeguarding the brain itself.”
Looking ahead, the researchers hope to explore whether interventions—dietary changes, improved oral care, even targeted probiotics—could meaningfully alter the gut environment and slow cognitive decline. There’s also potential for new biomarkers: if the toxins produced by these bacteria are measurable, they could one day help identify patients at high risk for Parkinson’s-related dementia before symptoms fully set in.
“We’re still in the early stages,” Clasen said. “But this opens a door. If we can confirm causality and understand the mechanisms, we might be able to intervene in a way that actually changes the course of the disease.”
For now, the message is clear: a toothbrush and a healthy diet might be more than routine—they might be neuroprotective tools hiding in plain sight.
