Gut bacteria linked to cognitive function in Parkinson’s, study finds

Gut bacteria may be more closely linked to cognitive function than movement symptoms in people with Parkinson’s disease, a study has found.

Biological markers associated with gut bacteria helped predict cognitive performance, although accuracy was modest. The same approach showed little ability to predict the severity of movement symptoms.

The findings suggest a relationship between cognitive difficulties and the gut microbiome, the community of microorganisms living in the digestive system.

Scientists in Malaysia analysed stool and blood samples from 67 people with Parkinson’s disease and 64 people without the condition.

They examined the composition of gut bacteria, substances produced by those bacteria and biological markers found in the blood.

The team used machine learning, a form of artificial intelligence that identifies patterns in data, to investigate how these markers related to Parkinson’s symptoms.

Models combining gut and blood markers were able to distinguish people with Parkinson’s from those without the condition with high accuracy.

They correctly identified more than 97 per cent of participants with Parkinson’s and more than 90 per cent of those in the control group.

The results are consistent with previous research suggesting that Parkinson’s affects biological processes beyond the nervous system.

Researchers then examined whether the same information could predict symptom severity using standardised clinical assessments.

Parkinson’s is commonly associated with movement symptoms such as tremors and slowed movement, but cognitive difficulties are also a recognised feature.

The models showed little or no predictive accuracy when assessing movement symptom severity.

They performed better when predicting cognitive outcomes, although accuracy remained modest despite the results being statistically significant.

Almost all the factors selected by the machine learning systems to predict cognitive performance were related to the gut.

These included levels of particular bacterial populations and metabolites, substances produced through biological processes involving gut bacteria.

Previous research has found differences in the composition and activity of gut bacteria in people with Parkinson’s disease.

However, the relationship between these changes and individual symptoms remains incompletely understood.

The latest findings suggest gut-related biological processes may be associated with cognitive difficulties, but they do not establish that changes in gut bacteria cause cognitive impairment.

The researchers also acknowledged the study’s relatively small number of participants, which limits the conclusions that can be drawn.

They called for larger studies to confirm the findings and investigate the relationship between gut bacteria and cognitive function in Parkinson’s disease.