Parkinson’s Disease (PD) is a progressive neurodegenerative disorder associated with brain changes, deficits in motor function, nonmotor symptoms, and cognitive decline. PD is characterized by motor dysfunctions including rigidity, tremor, and postural instability, and other symptoms such as sleep disturbance, anxiety, depression, constipation, and other gastrointestinal (GI) symptoms. Inflammation, mitochondrial dysfunction, and oxidative damage have been linked to PD. Recent evidence also suggests that changes in the gut microbiome may influence PD. 

A recently published review article by Mirzaei and colleagues explored the relationship between PD and probiotic supplementation. Multiple research studies have correlated changes in the gut microbiome with certain aspects of PD progression. The gut microbiome may influence cognitive functioning through many different pathways including neural, metabolic, neuroendocrine, and immune. The immune system has been shown to have a bidirectional influence on the gut-brain axis; levels of interleukin (IL)-1 and IL-6 may be modulated indirectly by certain microbiota and probiotics. In the hypothalamus, IL-1 and IL-6 may then regulate the release of corticotropin-releasing hormone, a regulator of the hypothalamic-pituitary-adrenal axis.

Reduced populations of species in the Prevotellaceae family in the gut microbiome have been linked to the incidence of PD. Prevotellaceae play a role in the synthesis of neuroactive short-chain fatty acids (SCFA) including butyrate, propionate, and acetate, as well as the release of folate and thiamine. Changes in butyrate concentrations may influence intestinal permeability. Intestinal permeability may then increase bacterial endotoxins such as lipopolysaccharides (LPS) which can lead to the overexpression and aggregation of alpha-synuclein, which is a protein linked to neuroinflammation, motor deficits, and PD.

Dopamine deficiency is a hallmark feature of PD. Changes in dopamine levels are also associated with the gut microbiome. Almost half of the dopamine in the body is produced in the GI tract. Changes in the gut microbiome have been shown to affect the production of dopamine through its influence on ghrelin. SCFAs were recently shown to help modulate ghrelin levels. 

GI microbes have also been shown to produce ferulic acid, a molecule that helps modulate the inflammatory response. Ferulic acid helps suppress reactive oxygen species and apoptotic activity through several pathways including the expression of caspase-3. 

Probiotic supplementation may support the production of neurotransmitters, a healthy inflammatory response, and healthy brain-derived neurotrophic factor (BDNF) levels. Reduced levels of BDNF have been associated with dopaminergic cell death in PD. A supplement containing Lactobacillus acidophilus, Lactobacillus reuteri, and Bifidobacterium bifidum was associated with improvement in certain symptoms related to PD in clinical studies. In animal studies, probiotic supplementation was shown to help improve motor impairment in PD animal models; improvements in spatial memory and rotational behavior were also noted.

Daily administration of Streptococcus thermophilus and Lactobacillus plantarum was shown to help improve motor skills. Another study involving Clostridium butyricum reported improvements in gait patterns, motor coordination, and balance. 

More clinical research is needed, particularly with standardized probiotic strains. However, research suggests that probiotics may help support certain aspects of brain health, cognitive function, and potentially play a supportive role in certain age-related neurodegenerative illnesses. 

By Colleen Ambrose, ND, MAT