New research links gut inflammation to Alzheimer’s, with higher levels associated with more amyloid plaque in the brain.
Animal studies have shown Alzheimer’s can be passed to young mice through gut microbe transfer, strengthening the link between the gut and the brain.
A 2023 study adds support to inflammation as a possible mechanism.
Barbara Bendlin, psychologist at the University of Wisconsin, said: “We showed people with Alzheimer’s disease have more gut inflammation, and among people with Alzheimer’s, when we looked at brain imaging, those with higher gut inflammation had higher levels of amyloid plaque accumulation in their brains.”
Margo Heston, pathologist at the University of Wisconsin, and an international team tested faecal calprotectin, a marker of gut inflammation, in stool samples from 125 individuals in two Alzheimer’s prevention cohorts.
Participants completed cognitive tests at enrolment, family history interviews and testing for a high-risk Alzheimer’s gene. Amyloid plaques are abnormal protein clumps in the brain that signal disease processes.
A subset of participants took clinical tests for signs of amyloid protein clumps.
Whilst calprotectin levels were generally higher in older participants, they were even more pronounced in those with Alzheimer’s-characteristic amyloid plaques.
Levels of other Alzheimer’s biomarkers also rose with inflammation, and memory scores fell as calprotectin increased. Even participants without an Alzheimer’s diagnosis recorded poorer memory with higher calprotectin.
Heston said: “We can’t infer causality from this study; for that, we need to do animal studies.”
Laboratory analyses have shown gut-bacteria chemicals can stimulate inflammatory signals in the brain. Other studies have reported increased gut inflammation in patients with Alzheimer’s compared with controls.
The researchers suspect microbiome shifts trigger gut changes that lead to mild but chronic, system-wide inflammation, gradually weakening the body’s protective barriers.
Federico Rey, bacteriologist at the University of Wisconsin, said: “Increased gut permeability could result in higher blood levels of inflammatory molecules and toxins derived from gut lumen, leading to systemic inflammation, which in turn may impair the blood-brain barrier and may promote neuroinflammation, and potentially neural injury and neurodegeneration.”
The team is now testing whether diet-induced inflammation in mice can trigger the rodent version of Alzheimer’s.
