Can gut bacteria quietly raise Alzheimer’s risk? New study has clues

New research shows that higher levels of this bacterial product may be associated with changes in the brain linked to Alzheimer’s disease. (Image: Pixabay)

What happens in the gut may have consequences far beyond digestion. Scientists are increasingly discovering that the trillions of microorganisms living in our intestines produce chemicals that can enter the bloodstream and influence metabolism, inflammation and the immune system. Now, researchers are investigating whether one of these microbial chemicals could also affect the ageing brain.

The molecule attracting attention is imidazole propionate, or ImP, which is produced by some gut bacteria.

What is imidazole propionate?

ImP is a small molecule made when certain bacteria break down an amino acid found in proteins.

New research shows that higher levels of this bacterial product may be associated with changes in the brain linked to Alzheimer’s disease. The findings, highlighted in a University of Wisconsin–Madison research announcement on October 3, came from research involving both humans and mice.

What did the researchers find?

The researchers studied 1,196 adults who did not have cognitive impairment. People who had higher concentrations of ImP in their blood tended to perform less well on certain cognitive tests. They also had more biological markers associated with Alzheimer’s disease. The researchers additionally found associations between some ImP-producing gut bacteria and Alzheimer’s-related markers.

But there is an important distinction here: an association is not proof of cause and effect. Having a higher level of ImP does not mean that a person will develop Alzheimer’s disease. To explore whether there might be a biological mechanism behind the association, the researchers turned to mice.

Could a gut chemical affect the brain?

In experiments, mice exposed to ImP over prolonged periods developed changes resembling some features of Alzheimer’s disease. These included alterations involving beta-amyloid and tau, two proteins closely associated with Alzheimer’s. In Alzheimer’s disease, beta-amyloid can accumulate as plaques, while abnormal tau can form tangles inside brain cells. The researchers also found evidence that ImP can affect the blood-brain barrier. The blood-brain barrier is a protective system formed largely by specialised cells lining blood vessels in the brain. It helps regulate which substances in the bloodstream can enter brain tissue. If this protective barrier becomes impaired, it may contribute to processes involved in brain ageing and neurological disease.

Story continues below this ad

Taken together, the findings suggest a possible pathway: Certain gut bacteria produce ImP. This enters the bloodstream, may affect the blood-brain barrier and brain cells, triggering changes associated with Alzheimer’s disease.

Does this mean probiotics could prevent Alzheimer’s?

No—not based on this study. The research did not test whether probiotic supplements can lower ImP levels or reduce the risk of Alzheimer’s disease. Probiotics contain different strains of bacteria, and one probiotic product cannot be assumed to have the same effects as another. In addition, the gut microbiome is extremely complex. Simply adding bacteria to the gut does not necessarily mean that the overall microbial environment will change in a predictable way.

The study also did not identify a particular food or diet that can reliably eliminate ImP.

Alzheimer’s disease has many risk factors

It is also important not to view Alzheimer’s disease as the result of a single molecule—or even a single biological pathway. Age is the strongest known risk factor, while genetics, cardiovascular health and other factors can also influence risk. Blood pressure, cholesterol, diabetes, physical activity, smoking, sleep and overall health are among the factors researchers continue to study. The gut microbiome may eventually turn out to be one piece of this much larger puzzle.

Story continues below this ad

Why is the finding important?

Looking at the chemicals produced by those bacteria may provide a more precise way of studying the gut–brain connection. Researchers can now ask questions such as: Which gut bacteria produce ImP? What causes those bacteria to make more or less of it? How much ImP enters the bloodstream? Can lowering ImP levels alter Alzheimer’s-related changes? Could targeting ImP or the bacteria that produce it be safe and effective in people?

These are the questions that future studies will need to answer. If future research in humans shows that lowering ImP can reduce Alzheimer’s-related changes or help preserve cognitive function, this early finding could eventually become the basis for a new therapeutic strategy.