Lots of research suggests that healthy hearts lower our risk of dementia.

But it seems gut changes might matter, too.

Dr David Vauzour, lead researcher of the paper published in Gut Microbes, said: “Even in people who had only just begun noticing mild memory changes, there were clear shifts in both their gut bacteria and the metabolites they release into the bloodstream”.

The researchers looked at stool samples from 150 adults aged 50 and over. Some were healthy, while others had mild cognitive impairment (MCI), sometimes seen as a precursor to dementia.

There was also a third group of people who performed normally on cognitive tests but who said they felt like something “wasn’t quite right” with their memory or cognition.

All participants gave the researchers both fasting blood samples (which were used to identify 33 key molecules made in our gut) and stool samples (used to identify the gut bacteria of participants).

“We explored whether specific combinations of these gut and diet-derived chemicals could separate the healthy from those experiencing early cognitive decline,” Dr Vazour said.

“What we found was really striking. Even in people who had only just begun noticing mild memory changes, there were clear shifts in both their gut bacteria and the metabolites they release into the bloodstream.”

They built a machine-learning model on just six of these metabolites. It was able to classify people into the three groups with 79% accuracy, and could tell cognitively healthy adults apart from those with mild cognitive impairment with over 80% accuracy.

The chemical changes seen in participants’ blood samples seemed to be linked to the bacteria present (or absent) in their stool, which Dr Vaxour said adds “weight to growing evidence that the so‑called gut–brain axis ― the communication network between our digestive system and the brain ― may play an important role in cognitive ageing”.

The study’s co-author, Dr Simon McArthur from Queen Mary University of London, has high hopes for the findings.

“While we’re not yet at the point of providing a diagnostic test, our work suggests we may be able to use dietary and microbial information to help catch the presence of dementia earlier in life, potentially even before significant brain damage has occurred,” he said.

“We hope this work will pave the way for simple, non-invasive blood tests capable of identifying people at higher risk of memory decline years before dementia is typically diagnosed.”

For his part, Dr Vauzor added, “If particular gut bacteria or the chemicals they produce contribute to early cognitive decline, treatments involving diet, probiotics, microbiome‑based therapies, or personalised nutrition could one day form part of dementia prevention strategies.”

However, writing for the Science Media Centre, Prof Eef Hogervorst, a Professor of Biological Psychology at Loughborough University, wasn’t as convinced.

He said, “It is an interesting finding and a very well-written paper with good theory and impressive statistical analyses, but with small groups and no follow-up, I think the conclusion that this can be an early diagnostic marker for cognitive decline and even dementia may be a little overstated.”