Is Alzheimer's Really a Brain Disease?

For over a century, Alzheimer’s disease has been viewed primarily as a degenerative brain disorder—one that progressively steals memories, cognition, and ultimately, identity. It’s no exaggeration to say it is one devastating illness that continues to haunt patients and families, still with no definitive cure. But here’s the twist: what if it’s because we’ve been looking in the wrong place all along? What if the origins of Alzheimer’s don’t begin in the brain, but deep within our gut?

This idea was not conjured out of thin air. In December 2024, a publication of a groundbreaking research by scientists at King’s College London and APC Microbiome Ireland gained serious attention in the medical field. They proposed that symptoms of Alzheimer’s could actually be transferred from one mouse to another—just by transplanting gut bacteria. A simple exchange of these gut microbes triggered brain inflammation, memory loss, and cognitive changes in healthy mice. 

This sensational finding acts as a clue that Alzheimer's may be more than just a brain disease. Maybe, it begins as an immune disorder that is triggered by microbial derangements in the gut.

In fact, in 2023, few scientists were already beginning to question the entrenched brain-centered understanding of Alzheimer's. Research done by the National Institute on Aging (NIA) revealed that symptoms of aging Alzheimer's patients were often accompanied by a sudden loss of beneficial gut microbes and a corresponding rise in inflammatory markers, these symptoms even showing up before the brain even started developing amyloid plaques (clumps of protein often seen in Alzheimer’s patients).

To fortify the theory that the gut microbiome impacts the brain, scientists at Duke University found that people with Alzheimer's had abnormal concentrations of bile acids in their blood and brain tissue—compounds that are broken down in part by the liver and finished off by bacteria in the gut. This suggests that these gut chemicals are able to cross the blood-brain barrier and interfere with neural functioning.

It is  becoming clearer that the brain and gut are deeply connected, constantly chatting through the gut-brain axis. One key player in this system is short-chain fatty acids (SCFAs), made when gut bacteria break down fiber. These molecules help calm down brain inflammation as well as regulate brain’s immune cells microglia, that, when overactive, are known to drive Alzheimer’s-related damage. 

The bottomline? Is Alzheimer's still a brain disease?

Perhaps. It is clear that the relationship between Alzheimer’s and the guts is strong, yet the research done so far is still too limited to prove causation. But one thing is made sure: the gut, once thought to play just a mere supporting role in brain health, is now stepping into the spotlight of upcoming multitudinous research. And who knows? This might not just reshape how we understand Alzheimer’s and research efforts for its cure, but many other diseases as well.

References

Alzheimer’s may not be a “brain disease.” (2024). Earth.com. https://www.earth.com/news/alzheimers-may-not-be-a-brain-disease/

Piller, C. (2022, July 21). Potential fabrication in research images threatens key theory of Alzheimer’s disease. Science. https://www.science.org/content/article/potential-fabrication-research-images-threatens-key-theory-alzheimers-disease

The Conversation. (2025, March 20). Alzheimer’s May Not Actually Be a Brain Disease, Says Expert. ScienceAlert. https://www.sciencealert.com/alzheimers-may-not-actually-be-a-brain-disease-says-expert