A Microbial Signature of Dementia

Gut microbes are significantly different in people with cognitive impairments.

“We have to get behind the scientists and push for a dementia breakthrough. It could be that we fear dementia out of a sense of hopelessness, but there is hope, and it rests in the hands of our scientists.” —James Nesbitt

People with fewer and less-diverse gut microbes are more likely to have cognitive impairment, including dementia and Alzheimer’s. That’s according to a new study from a collaboration between Monash University of Australia and Jinan University of China.

Far from being a horrifying inevitability, this is excellent news. We can’t change our DNA or our upbringing, but we have a lot of control over our gut microbes. We just need to eat better and move a little more. Many of us have made it our life’s goal to maximize our sedentary snacking, but sadly, that is doing us no favors.

The study also found that pathogenic bacteria, including Pseudomonas, were more prevalent in people with cognitive impairment. Pseudomonas can stimulate the production of amyloids, which are known to be involved with Alzheimer’s and Parkinson’s. Amyloids are intimately involved with cognition and brain function.

The Amyloid Connection

Amyloids are a type of protein that are built to stack together like LEGO bricks. They are versatile components of all sorts of biological processes. Bacteria—like Pseudomonas—use amyloid proteins to stitch together communities of like-minded microbes into a tough matrix called a biofilm. But amyloids are not unique to bacteria; our gut lining produces amyloids in the form of antimicrobial proteins that act like fish nets, capturing pathogenic bacteria and then flushing them from our system.

But the amyloid that most people have heard about is in our brain. It forms plaques that disrupt the delicate information processing of our nerve cells. They grow to such huge numbers that they can be seen under an ordinary microscope, as Alois Alzheimer discovered in 1906 when he examined the brain of a dementia patient.

Most scientists working in the field today believe that amyloid is the cause of Alzheimer's, but a growing number of renegade researchers believe that amyloid in the brain is like the amyloid in the gut: a trap for pathogenic bacteria. If that is true, then the origin of Alzheimer's may be microbial, and amyloid buildup is the result, not the cause. When it comes to brain inflammation, we may have mistaken the firemen for the arsonist.

The study also found that beneficial bacteria like Blautia, Megamonas, and Veillonella were enhanced in the control group. Keep in mind that these three genera encompass many different species, most of which are beneficial, but some of which may be less so. Further studies will be needed to drill down to the species level to find out who the individual players are.

What to Do

The study was fairly small, with 229 people 60 years and older. But it showed causality, a rarity in human studies. They asked a group of their subjects to get more fruit and exercise into their lives and found that the richness of microbes in their gut improved.

Lead author Lei Zhang says, “Our findings reveal that consuming fresh fruit and engaging in regular exercise help promote the growth of gut microbiota, which is beneficial for cognitive function and can protect against cognitive impairment.”

The best fruit for gut microbes is berries. Strawberries, blackberries, blueberries, and raspberries are special fruits because we eat their seeds. This leads to a higher fiber content, which is what gut microbes really love. I’ve written about fiber and cognition before; you can read about it here.

Raspberries and blackberries contain about 9 grams of fiber per cup. A surprising winner in the fibrous fruit competition is passion fruit, with an amazing 24 grams of fiber per cup, if you eat the seeds. Not all fiber comes from seeds: avocados are often left off the fruit list, but they are actually fruit. They clock in at 9 grams of fiber per cup, and they also contain healthy oils.

Fiber feeds Megamonas bacteria, which then produce a healthy fatty acid called propionate. Fatty acids are like nectar to the cells lining your gut, both nourishing them and healing them. That keeps pathogens and toxins out of the blood system, preventing inflammation.

Flavonoids from fruit feed Blautia, a probiotic with many healthy characteristics. You can read more about flavonoids here. Blautia produces substances that kill pathogenic bacteria, even antibiotic-resistant ones. It also tells the immune system to chill out, preventing unnecessary inflammation. For that reason, Blautia may even protect against cancer.

As for exercise, it doesn’t need to be athlete-caliber to benefit us. But it needs to be more than running a bath or jumping to conclusions. One benefit of exercise is that it increases the abundance of Veillonella. This bacterium consumes the lactate generated by our exertions and converts it into propionate as well.

Is this a hassle? Well, fruit is nature’s original snack, and it’s easy to pop some berries in your mouth. Sadly, for the exercise-averse, there’s no great news. But if you think exercise is awful, just try dementia. This study will need to be replicated, but it’s some rare good news on the Alzheimer’s front.

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References

Wang, Jing, Gong Zhang, Hao Lai, Zengbin Li, Mingwang Shen, Chao Li, Patrick Kwan, et al. “Characterizing Gut Microbiota in Older Chinese Adults with Cognitive Impairment: A Cross-Sectional Study.” Journal of Alzheimer’s Disease. 2024 Aug 30. doi: 10.3233/JAD-240597. Online ahead of print.