How harmful gut bacteria trigger Alzheimer's

A growing body of evidence now suggests that it is not only age — but also diet — that affects the brain.

Indeed, a correlation between Alzheimer’s disease and an unhealthy gut has been uncovered, and Australian scientists are hoping to take this a step further by exploring how harmful gut bacteria access the brain and lead to dementia.

According to University of South Australia nano bio-scientist Dr Ibrahim Javed, tiny metabolites released by bad bacteria in the gut can travel to the brain, causing inflammation and triggering Alzheimer’s disease — for which there is no cure.

In younger people this is less likely because the blood–brain barrier is much stronger. However, this barrier weakens as people age, allowing harmful substances to damage neurons. When the microbiome in the gut ages, it also loses the ability to fight disease.

By identifying how metabolites released by bad bacteria damage neurons — and hopefully developing new drug therapies to block them — Javed said it should be possible to slow down or halt the progression of Alzheimer’s.

A second aim of the three-year research project is to investigate how probiotics and nutritional supplements, both of which contain friendly bacteria, can stamp out bad bacteria and stop metabolites escaping from the gut.

This follows on from several international clinical research studies that have demonstrated that probiotics improve digestive and cognitive issues in people with acute and chronic COVID-19.

“Our research indicates that harmful gut bacteria can trigger early onset dementia as well as accelerate dementia in patients already battling the neurodegenerative disease,” Javed said.

“A poor diet is one of several factors that harm gut bacteria, increasing your chances of developing dementia. Aging, lack of exercise, exposure to pesticides and genetics also play a role, although the latter is responsible for a very small number of cases. In most cases, dementia is preventable.”

Most types of bacteria are harmless — many are even essential for human survival — but bad bacteria create biofilms which cause gastrointestinal infections, chronic diseases, bowel cancer and brain diseases.

Alzheimer’s disease affects up to 55 million people worldwide and with an aging population, this number is expected to double every 20 years, according to Alzheimer’s Disease International.

Early onset dementia — under the age of 65 — is becoming more common in the global population, attributed to preventable factors such as a poor diet and a sedentary lifestyle, smoking, excessive alcohol consumption, social isolation, exposure to pesticides and air pollution.

Javed’s team is also collaborating with UniSA neuroscientist Associate Professor Larisa Bobrovskaya on a potential link between stress and Alzheimer’s disease, and whether women are more at risk.

Image credit: iStock.com/Ibrahim Akcengiz