https://orcid.org/0000-0003-2351-0444
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ABSTRACT
Background
The pathology underlying cognitive changes in people with Parkinson’s disease (PD) is not well understood. In healthy older adults, gut microbiome composition has been associated with cognitive function. In people with PD, preliminary evidence suggests that cortical spreading of abnormal alpha-synuclein aggregates may be associated with cognitive impairment. As changes in the gut have been linked to PD onset and associated Lewy body pathology, an investigation of the gut microbiome and cognition in PD is warranted.
Objective
To synthesise existing evidence on the relationship between the gut microbiome and cognitive function in PD.
Methods
A systematic review was conducted to search for peer-reviewed articles and grey literature published to July 2021 across seven electronic databases (MEDLINE, EMBASE, PsycINFO, Scopus, Cochrane Library, ProQuest, and ProQuest Dissertations and Theses). English language articles reporting the relationship between cognition and the gut microbiome in human participants with PD were considered for inclusion. Results were qualitatively synthesised and evidence quality was assessed using the QualSyst tool for quantitative studies.
Results
Five cross-sectional studies reporting the association between the gut microbiome and cognition in 395 participants with PD were included. Studies provided preliminary evidence of a relationship between cognition and gut microbiota within the Bacteroidetes and Firmicutes phyla, however, associations with specific genera were inconsistent across studies.
Conclusions
Some species of short-chain fatty acid-producing bacteria (e.g. acetate, butyrate, and propionate producers) appear to be reduced in participants with PD with cognitive impairment. More research with larger samples and more consistent methodology is needed to substantiate these findings.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Data availability statement
Data sharing is not applicable to this article as no new data were created or analysed in this study. The authors confirm that the information supporting the findings of this review are available within the article and its supplementary materials.
Additional information
Notes on contributors
Hayley Grant
Hayley Grant is a PhD candidate at Curtin University, Western Australia. She holds a Bachelor in Psychology (Hons).
Ryan Anderton
Ryan Anderton is an Associate Professor at the University of Notre Dame Australia. He holds a PhD in Neuroscience from the University of Western Australia. His current research focuses on the role of the gut microbiome and inflammation in influencing Parkinson’s disease initiation and progression.
Natalie Gasson
Natalie Gasson is a Professor of Psychology at Curtin University, Western Australia. She also completed her PhD in Psychology at Curtin University, and her research interests include ageing and Parkinson’s disease, stigma toward mental illness, and psychological literacy.
Blake J. Lawrence
Blake J. Lawrence is a Research Fellow at Curtin University, Western Australia. He also completed his PhD at Curtin University, which examined nonpharmacological interventions for mild cognitive impairment in Parkinson’s disease.