A new study is building on the growing association between the liver and Alzheimer's disease. Suggesting a correlation between blood-based liver function biomarkers and several neurological signs of Alzheimer's, the research hypothesizes the neurodegenerative disease has broader metabolic effects in organs other than the brain.

Several studies published over the past few years have found intriguing connections between Alzheimer's disease and the liver. Just last year it was suggested that an age-related decline in plasmalogens, a class of lipids produced by the liver, could be related to an increased risk of Alzheimer's. Other studies have previously found certain enzymes produced by the liver can confer neuroprotective effects, implying a dysfunctional liver can possibly precede the onset of neurodegenerative diseases such as Alzheimer's.

"While we have focused for too long on studying the brain in isolation, we now have to study the brain as an organ that is communicating with and connected to other organs that support its function and that can contribute to its dysfunction," explains Rima Kaddurah-Daouk, from Duke University, and one of the lead researchers on the new study. "The concept emerges that Alzheimer's disease might be a systemic disease that affects several organs including the liver."

The new study set out to fill a gap in the current body of scientific knowledge, looking to uncover any potential association between liver function biomarkers and Alzheimer's biomarkers. A cohort of more than 1,500 subjects was studied, including around 400 healthy controls. Several Alzheimer's biomarkers were tracked, including amyloid and tau levels in cerebrospinal fluid, against five standard liver-function markers easily detected in blood samples.

The results revealed a consistent association between alterations in liver function and the progression of Alzheimer's markers. The researchers are cautious to note that it is unclear at this stage whether these liver function alterations are playing a causative role in the progression of Alzheimer's. While prior research has described more overtly how the liver could be directly influencing neurodegeneration, this study more generally suggests an interesting "axis of communication" between the liver and the brain.

At the very least the study hypothesizes these liver function biomarkers, easily tracked through regular blood testing, could offer clinicians new ways to identify patients at a higher risk of developing Alzheimer's. Kwangsik Nho, a radiologist from the Indiana University School of Medicine working on the new study, also suggests this novel brain-liver association points to new ways to understand how Alzheimer's may have broad systemic signs outside of just the brain.

"This is a new paradigm for Alzheimer's research," says Nho. "Until now, we only focused on the brain. Our research shows that by using blood biomarkers, we can still focus on the brain but also find evidence of Alzheimer's and improve our understanding of the body's internal signalling."

The new research was published in the journal JAMA Network Open.