Dementia with Lewy bodies (DLB) is a common form of dementia that currently has no cure.
Recent research has suggested that gut bacteria may play a role in Parkinson’s disease, but the specific microbes associated with Lewy body dementia have remained unclear.
Now, a research team led by Nagoya University in Japan has identified three gut bacteria associated with DLB: Collinsella, Ruminococcus, and Bifidobacterium.
The findings could open new possibilities for diagnosis and treatment of the disease.
What is Lewy body dementia?
Lewy body dementia occurs when abnormal deposits of a protein called alpha-synuclein accumulate in the brain. These deposits disrupt brain chemicals and lead to declines in thinking, reasoning, memory, and movement.
Common symptoms include confusion, memory loss, impaired motor function, sleep disturbances, and visual hallucinations.
Parkinson’s disease typically begins with movement problems, but some patients develop cognitive decline within a year — a condition classified as Lewy body dementia. Predicting which patients will progress to DLB has been challenging for physicians.
What the study involved
The researchers analyzed gut microorganisms and fecal bile acids in patients with Lewy body dementia, Parkinson’s disease, and rapid eye movement sleep behavior disorder.
They found that three intestinal bacteria — Collinsella, Ruminococcus, and Bifidobacterium — were strongly associated with patients with DLB.
The team also observed similarities between the gut microbiomes of Parkinson’s disease and Lewy body dementia. In both conditions, bacteria that produce short-chain fatty acids (SCFAs), which are important for gut and brain health, were reduced.
In patients with DLB specifically, levels of Ruminococcus torques and Collinsella were increased, while Bifidobacterium levels were decreased.
Why these bacteria matter
Lower levels of Bifidobacterium may have important implications for treatment. This bacterium helps increase brain-derived neurotrophic factor (BDNF), a protein essential for the growth, development, and maintenance of neurons. Reduced Bifidobacterium levels may therefore contribute to cognitive decline in DLB.
Meanwhile, both Ruminococcus torques and Collinsella produce enzymes that influence inflammation in the substantia nigra, a brain region involved in movement control.
Higher levels of these bacteria in DLB compared with Parkinson’s disease may help explain why movement symptoms appear later in Lewy body dementia — a key difference between the two conditions.
Implications for diagnosis and treatment
The researchers suggest that gut microbiome analysis could help identify patients at risk of Lewy body dementia.
They also propose that targeting gut bacteria may offer new treatment strategies. Increasing Bifidobacterium levels could potentially slow disease onset and progression, while modifying levels of other bacteria might influence neuroinflammation.
Although more research is needed, these findings highlight the gut–brain connection as a promising area for future therapies.
The study was conducted by Hiroshi Nishiwaki and colleagues and published in npj Parkinson’s Disease.
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