It is only in recent years that science has begun to explore the role that bacteria in the digestive system play in the context of human health.
A recent study has discovered that they are much more influential than previously thought, directly affecting the brain.
The Brain-Gut Connection
The human body contains ten times more bacteria than it does human cells. It is estimated that the gut (where most of these bacteria live) contains over three million unique bacterial genes of one thousand different species—one hundred fifty times more than our own genes (1). Most of these bacteria are not only beneficial but necessary for proper body function.
Unfriendly bacteria can cause illness but the body knows enough to attack and kill those that are harmful. If, however, the “good” bacteria are compromised, the immune system weakens and disease can ensue.
Studies into all the ways in which internal bacteria affect health have revealed some surprising results.
A common perception is that the brain controls all the body’s systems. Links have been found that show the brain’s influence on the gut function. But, it turns out, that it’s a two-way street: microbiota in the gastrointestinal tract influence brain function, including cognition, memory, and motor activity.
An Unlikely Parkinson’s Disease Cause
Parkinson’s disease is a chronic and progressive disorder that affects motor control and cognition. Neurons in the brain that regulate the production of the hormone dopamine begin to die.
the reduction in dopamine levels affects motor function, resulting in:
- Tremors in the head, hands, arms, and legs
- Stiff or rigid arms, legs, and torso
- Slow body movement
- Loss of balance, sometimes progressing to the inability to stand
- Sleep irregularity
- Loss of the sense of smell
- Change in voice
The exact cause of Parkinson’s disease has been previously unknown. It has been theorized that it is partly genetic but predisposition doesn’t always manifest in symptoms. Environmental factors such as herbicides and pesticides, pharmaceuticals, chronic inflammation (the result of any combination of factors, including poor dietary habits, aspartame, food additives, stress, and lack of exercise), and other toxins contribute to the risk of developing Parkinson’s and other neurological diseases.
In a recent study, the two-way street between the brain and the gut were very clearly observed.
The results of the study begin with: “The intestinal microbiota influence neurodevelopment, modulate behavior, and contribute to neurological disorders. However, a functional link between gut bacteria and neurodegenerative diseases remains unexplored.”
Synucleinopathies are the group of neurodegenerative disorders characterized by the collection of α-synuclein proteins around neurons (nerve cells) and glia (brain cells that support neurons, transporting nutrition and removing waste). α-synuclein is a protein normally found in the brain; in the case of synucleinopathies, there occurs an over-accumulation of them. Parkinson’s disease is included in this group.
The mice used in the study were treated to over-produce α-synuclein. Scientists found that the administration of antibiotics exacerbated the loss of motor control and other Parkinson’s symptoms. When the mice were orally fed probiotics (normal gastrointestinal bacteria), motor function improved and brain activity increased. Other groups of α-synuclein over-producing mice in the study were given microbiota directly from healthy people and people diagnosed with Parkinson’s. The reaction in the mice: symptoms worsened after receiving bacteria from the Parkinson’s donor group.
The study concluded: “These findings reveal that gut bacteria regulate movement disorders in mice and suggest that alterations in the human microbiome represent a risk factor for PD [Parkinson’s Disease].” (2)
The Importance Of Gut Bacteria
Synucleinopathies are not the only neurological conditions affected by gut bacteria.
If further proof is needed of the connection between healthy bacterial levels and the brain, here it is. A 2013 study linked gut bacteria to autism spectrum disorders (ASD). Symptoms were stimulated by the introduction of harmful bacteria and alleviated with the administration of probiotic bacteria. References to other studies point to a similar connection between brain and gut when studying multiple sclerosis, anxiety, and emotional instability.
“…microbial shifts within the gut of a mouse resulted in changes of metabolites in the serum and that these lead to the onset of autism-like behaviors. Moreover, administering a beneficial bacterium, Bacteroides fragilis, reversed the physiological, neurological, and immunological anomalies.” (3)