The fountain of youth does not exist, but there is a nauseating-sounding procedure that could keep us sharp into old age.
Writing in the journal Nature Aging, scientists from University College Cork revealed how they transferred bacteria from the faeces of young mice into older rodents.
While it may sound unpleasant, the safe procedure "reversed ageing-associated differences" to the older animals' so-called "brain immunity", in a move that has been called a "potential game-changer".
"Age-associated impairments in cognitive behaviour" were also reduced among the transplant recipients.
Although it is early days, so-called faecal microbiota transplants (FMTs) "may be a suitable therapeutic target to promote healthy ageing".
In the meantime, the scientists hope people will look after their gut health. Eating a nutritious diet that is rich in probiotics – found in certain yoghurts, sauerkraut and miso – can preserve the "good bacteria" that reside in our gastrointestinal tract.
Speaking of the results, study author Professor John Cryan said: "It's a potential game-changer. We've now established the microbiome can be harnessed to reverse age-related brain deterioration.
"We also see evidence of improved learning ability and cognitive function.
"Friendly bacteria have beneficial effects on the metabolic and immune systems. They can be gradually replaced with bacteria that drive chronic inflammation, metabolic dysfunction [a reduced ability to convert food into energy] and disease.
"We know microorganisms in the gut shape local immunity, but can also affect brain ageing and increase the risk of neurodegenerative diseases.
"Much work is needed to translate the findings for clinical use in humans," he added.
FMTs are approved in the UK if "standard therapies fail to help with diarrhoea" caused by the bacteria Clostridioides difficile.
The procedure involves the waste of a healthy donor being processed and then transplanted into a patient's intestine. This helps to restore the balance of the patient's gut bacteria, fighting off a C. difficile overgrowth.
While a FMT may sound off-putting, donors are first tested for an array of infections. They must also be free of medical problems and lead a healthy lifestyle.
C. difficile aside, our gut bacteria are increasingly being linked to our immune system and brain health.
Ageing is known to trigger "dramatic alterations in the microbiota, which is linked to poorer health and frailty in elderly populations", wrote the Cork scientists.
To better understand the potential of FMTs to ease "ageing processes", the team transplanted the gut bacteria of young – aged three to four months – and old – aged 19 to 20 months – mice into other rodents, also aged 19 to 20 months.
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The animals that received the gut bacteria of the young donors went on to perform better on memory tasks, as well as deciphering maze patterns more quickly.
Scans also showed signs of brain rejuvenation among the recipients, with their vital organ more closely resembling that of a younger mouse.
The recipients were also less prone to anxiety, a common dementia symptom.
"Our results reveal the microbiome may be a suitable therapeutic target to promote healthy ageing," wrote the scientists.
Professor Cryan has stressed, however, the findings should direct focus towards "microbiota-targeted dietary or bacterial-based interventions", rather than "advocating faecal transplants for people who want to rejuvenate their brain".
A daily dose of probiotics has previously been linked to improved health outcomes among older people.
"This research further demonstrates the importance of the gut microbiome in many aspects of health and particularly across the brain-gut axis where brain functioning can be positively influenced," said Professor Paul Ross, also from University College Cork.
"The study opens up possibilities in the future to modulate gut microbiota as a therapeutic target to influence brain health."
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