A blood test could help identify people at higher risk of cognitive decline years before a traditional diagnosis is possible – according to University of East Anglia research.
Scientists have discovered that subtle changes in the blood may reveal the earliest signs of cognitive decline long before symptoms become obvious.
These changes are caused by chemicals produced by gut bacteria - reinforcing the idea that the gut–brain connection plays an important role in early memory changes.
It is hoped that the breakthrough could one-day transform how we detect dementia.
Lead researcher Dr David Vauzour, from UEA's Norwich Medical School, said: "Dementia is one of the greatest public health challenges of our time.
"Around a million people in the UK are living with the condition, and globally more than 55 million people are affected. With cases projected to increase sharply as populations age, the urgency for earlier detection, better support, and meaningful prevention strategies has never been greater.
"Early detection is critical because by the time dementia symptoms become obvious, much of the brain damage has already happened.
"Identifying biological warning signs earlier could allow for timely lifestyle changes, targeted interventions, and better monitoring."
How the research happened
Researchers analysed blood and stool samples from 150 adults aged 50 and over - ranging from healthy individuals to those with mild cognitive impairment (MCI), which is often a precursor to dementia.
A third group included people experiencing subjective memory lapses, who still perform normally on standard cognitive tests but feel that something is "not quite right".
The volunteers gave fasting blood samples, which were scrutinised using highly sensitive lab techniques to measure 33 key molecules produced by the gut microbes and from diet.
Participants also provided stool samples so scientists could map the unique communities of bacteria living in their digestive systems.
Dr Vauzour said: "Using advanced computer modelling and AI-powered machine learning, we explored whether specific combinations of these gut and diet derived chemicals could separate the healthy from those experiencing early cognitive decline.
The gut–brain warning signals hiding in plain sight
"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."
A machine-learning model built on just six of these metabolites was able to classify people into the three groups with 79 per cent accuracy and could distinguish healthy adults from those with mild cognitive impairment with over 80 per cent accuracy.
"Crucially, the chemical changes in the volunteers' blood were strongly linked to differences in specific gut bacteria," said Dr Vauzour.
"This 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 aging.
Paving the way for a dementia blood test
"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," added co-author Dr Simon McArthur, from Queen Mary University of London.
"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."
The study also highlights the potential of the gut microbiome as a target for protecting brain health.
Dr Vauzour said: "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."
Dr Saber Sami, Alzheimer's Research UK UEA lead and co-author, said: "This study is exciting because it links advanced data analysis with a clinically realistic goal of finding a simple and acceptable way to detect risk earlier. It could add to a new set of methods that help bridge the gap between discovery science and practical tools for prevention."
This research was led by the University of East Anglia in collaboration with Queen Mary University of London. It was part-funded by Alzheimer's Research UK.
'Circulatory dietary and gut-derived metabolites predict early cognitive decline' is published in the journal Gut Microbes.
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