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.

New research has linked richer social ties to better cognitive health in older adults, offering new insight into how connection relates to thinking and memory.

Earlier studies found links between specific social factors and health.

This study appears to be the first to build combined social profiles and test how they relate to cognitive health in older adults.

An interdisciplinary team from McGill University and Université Laval created three social environment categories, described as weaker, intermediate and richer.

They assembled 24 social variables such as network size, support, cohesion and isolation using data from about 30,000 participants in the Canadian Longitudinal Study on Aging, a nationally representative cohort of randomly selected Canadians aged 45 to 84 at baseline.

For cognition, the researchers examined three domains: executive function, which involves planning and decision-making; episodic memory, the ability to recall past events; and prospective memory, the ability to remember to perform planned actions.

They used data from a battery of tests previously administered to participants.

Daiva Nielsen is associate professor at the McGill School of Human Nutrition and co-first author of the paper

Nielsen said: “We identified significant associations between the social profiles and all three cognitive domains, with the intermediate and richer profiles generally exhibiting better cognitive outcomes than the weaker profile.”

The researcher noted that the effect size of the associations, a statistical measure of the strength of the relationship between variables, was relatively small, which is consistent with previous studies.

Nielsen noted that the effect sizes were somewhat stronger for participants aged 65 or older.

According to the researcher, this suggests that the social environment-cognition association may be more significant later in life.

Awareness has been increasing of the importance of social connection in public health.

Lack of social connection has been shown to be comparable to more widely acknowledged disease risk factors such as smoking, physical inactivity and obesity.

It is important to translate this knowledge to the public to empower individuals to help build meaningful connections within their communities.” she said.

The authors noted that the observed associations are correlational rather than causal, and it is possible, for example, that poor cognitive health also leads individuals to withdraw from social life.

The team, whose members span marketing, human behaviour, nutrition and epidemiology, hopes to continue using the Canadian Longitudinal Study on Aging data and the newly created social profiles in future research, said Nielsen.

The next steps involve studying changes in social environments and various health-related outcomes, including diet and chronic disease risk, she added.

“This work is an excellent example of the benefits of multidisciplinary research teams that can tackle complex research questions and bring diverse knowledge and expertise.” she said.