Does Parkinson's Disease Start in the Gut?

A Rise in Parkinson's Cases

The number of people with Parkinson’s disease across the world has doubled in the past 25 years. Parkinson’s is the fastest growing neurological disorder worldwide, even surpassing Alzheimer’s disease, according to the Global Burden of Disease Study, which pooled health outcomes data from 195 countries.

A Link to the Gut

There is growing evidence linking Parkinson's disease to poor gut health. Several studies suggest that gut dysfunction may play a key role in the development and progression of the disease.

“People have, for the longest time, described Parkinson’s disease as a top-down disease - so, it starts in the brain and then percolates down to the gut, and that’s why patients have issues with their gastrointestinal tract,” said study author Subhash Kulkarni, an assistant professor at Beth Israel Deaconess Medical Centre in the US.

“Another hypothesis suggests that, in many patients, it may be a bottom-up approach, where it starts in the gut and goes all the way up to the brain.”

Kulkarni and his colleagues found that people with upper gastrointestinal conditions, in particular, ulcers or other types of damage to the lining of the oesophagus, stomach, or upper part of the small intestine, were far more likely to develop Parkinson’s disease later in life. The study was published online Thursday in Jama Network Open.

Gut-Brain Axis

The "gut-brain axis" refers to the communication network between the digestive system and the brain. Parkinson’s disease may begin in the gut, with gastrointestinal symptoms like constipation often appearing years before motor symptoms. Some researchers believe that misfolded alpha-synuclein proteins, a hallmark of Parkinson's, may form in the gut and travel to the brain via the vagus nerve.

Gut Microbiome

Changes in the gut microbiome, the population of bacteria in the intestines, have been observed in Parkinson’s patients. Studies show that Parkinson’s patients often have an altered balance of gut bacteria (dysbiosis), with fewer beneficial bacteria and an increase in harmful species. These imbalances may influence inflammation and neurodegeneration.

Intestinal Permeability ("Leaky Gut"):

Some research suggests that patients with Parkinson's may have increased intestinal permeability, commonly known as "leaky gut." This can allow harmful substances like toxins or pathogens to escape from the gut into the bloodstream, potentially triggering inflammation that affects the brain.

Gastrointestinal Symptoms:

Many people with Parkinson’s experience gastrointestinal issues like constipation, bloating, or difficulty swallowing years before developing motor symptoms. This has led researchers to investigate the early involvement of the gut in Parkinson’s pathology.

Vagus Nerve Involvement:

The vagus nerve, which connects the brain and the gut, may play a role in the transmission of pathological proteins from the gut to the brain. Some animal studies have shown that cutting the vagus nerve can delay or prevent the onset of Parkinson’s-like symptoms, suggesting a pathway between gut health and brain disease.

While these findings are not yet fully understood, they highlight the potential role of gut health in Parkinson’s disease and suggest that the gastrointestinal system could be an early site of disease activity. This has led to an increased interest in therapeutic approaches like probiotics, prebiotics, and dietary interventions aimed at improving gut health as a way to potentially slow the progression of Parkinson’s.