Uncovering the Link Between Gut Bacteria and Alzheimer's Disease

Alzheimer's disease is a wily opponent that has long confounded even the most brilliant scientific minds. Still, researchers continue their pursuit of a cure and have nailed down a slew of risk factors, including everything from genes to circulatory issues, chronic inflammation, and lifestyle habits.

Researchers have discovered yet another factor that may boost one's Alzheimer's risk: the type of bacteria living in the gut microbiome. Studies suggest that a person's microbiome changes with age, environmental, and lifestyle factors. And several other studies suggest the microbiome may influence the development of neurodegenerative diseases, such as Alzheimer's disease. 

Here at Brain Health Breakthroughs, we are dedicated to bringing you the most credible and up-to-date findings. Through the years, we've followed emerging research regarding Targeting the Gut for a Better Brain, and how to Boost These Gut Microbes and Calm Depression.

This blog post delves into the complex world of human gut microbiota and neurodegenerative diseases. We'll cast the spotlight on the link between gut bacteria and Alzheimer’s disease and what researchers have discovered via meta-analysis, fecal samples, and Alzheimer's disease patients. Lastly, we will offer some practical tips for you to foster a healthy gut microbiome that will benefit brain function today and in the future. 

Key Takeaways

• Experts now believe that the gut-brain axis may contribute to the development and progression of neurological diseases such as Alzheimer’s disease.
• A growing body of research suggests that certain bacteria in a person's gut microbiome can affect their overall health and longevity and may be an early marker for developing dementia.
• Potential therapies include probiotics, prebiotics, dietary changes, exercise, sleep optimization, and fecal matter transplant (FMT).

Understanding the Gut-Brain Axis

The gut-brain axis is the two-way communication between the digestive system and the central nervous system. Residing in your digestive system, this "second brain" has been the focus of much research. 

Scientists have widely acknowledged that the microbiome-- or the gastrointestinal ecosystem-- affects overall health. However, it's only within the past 15 years that they have come to recognize that this gut-brain axis is vital for brain health. Now, many experts believe that it's closely linked to the development and progression of Alzheimer’s disease.

According to the National Institutes of Health, Alzheimer’s disease is a progressive neurodegenerative disease that slowly destroys memory and thinking skills, and eventually, the ability to carry out the simplest tasks. This neurological disease is the most common form of dementia, affecting millions of people worldwide.

The Role of Gut Microbiota

Gut microbiota is the complex community of microorganisms -- including bacteria, fungi and viruses -- that reside in your gastrointestinal tract and are essential for sustaining regular physiological homeostasis. These tiny yet mighty inhabitants can significantly modulate brain function and have been implicated in various brain diseases, and as a risk factor for Alzheimer’s.

According to a 2022 meta-analysis published in the journal Nutrients "a growing body of evidence indicates that gut microbiota dysfunctions are involved in the early stages of AD pathogenesis."

Inflammation and Immune System Dysfunction

Chronic inflammation and immune system dysfunction in the brain are closely associated with Alzheimer’s disease, and gut bacteria play a significant role in stopping or improving gut inflammation. A new study from Washington University School of Medicine, has found that gut bacteria influence immune responses in mice.

One analysis compared healthy people and people with preclinical Alzheimer's disease. Scientists found that the two groups had "markedly different gut bacteria" despite eating the same diet. These differences correlated with amyloid and tau levels, which rise long before cognitive symptoms appear. Researchers reason that these differences could be used to screen for early Alzheimer's disease.

“If there is a causative link, most likely the link would be inflammatory,” says study co-author Guatam Dantas, PhD. “Bacteria are these amazing chemical factories, and some of their metabolites affect inflammation in the gut or even get into the bloodstream, where they can influence the immune system all over the body."

Dr. Dantas admits that it's all speculative at this point. "But if it turns out that there is a causal link, we can start thinking about whether promoting ‘good’ bacteria or getting rid of ‘bad’ bacteria could slow down or even stop the development of symptomatic Alzheimer’s disease.”

Key Gut Bacteria Associated with Alzheimer's Disease

Recently published research from the University of Nevada, Las Vegas found a significant correlation between 10 specific types of gut bacteria and the likelihood of developing Alzheimer's disease.

Six of these bacteria were dubbed protective, while the other four were identified as risk factors for the disease. These bacteria play a critical role in the development of cognitive decline, which is a hallmark of Alzheimer’s disease.

Risk Factors: Four Harmful Bacteria

Four harmful bacteria—Collinsella, Bacteroides, Lachnospira, and Veillonella—are linked to increased Alzheimer’s disease risk due to their role in inflammation and immune dysfunction. Bacteroides, in particular, has been identified as the most significant risk genus linked to Alzheimer’s disease.

In addition to these four bacteria, other harmful microorganisms, such as Porphyromonas gingivalis, Chlamydia pneumoniae, Spirochetes, and fungi, have also been associated with Alzheimer’s disease. Identifying and targeting these harmful bacteria may provide valuable insights that can be leveraged in the fight against Alzheimer’s disease.

Protective Factors: Six Beneficial Bacteria

On the other hand, six categories of beneficial bacteria—Adlercreutzia, Eubacterium nodatum group, Eisenbergiella, Eubacterium fissicatena group, Gordonibacter, and Prevotella—are associated with a reduced risk of Alzheimer’s disease, potentially due to their anti-inflammatory properties.

For instance, Intestinibacter has been identified as the most significantly associated protective genus with Alzheimer’s disease.

By promoting the growth of these beneficial bacteria and improving the microbial composition of the gut, we may be able to harness their protective effects and develop targeted interventions to prevent or treat Alzheimer’s disease.

More on how you can start doing this on your own in a minute. But first, why do the bacteria have such a beneficial effect on the brain?

Is Alzheimer's Disease a Metabolic Disorder?

Studies have suggested that Alzheimer’s disease is a metabolic disorder, with disruptions in various metabolic pathways, including tryptophan, tyrosine, and purine pathways.

Metabolic pathways involving gut bacteria-derived metabolites, such as short-chain fatty acids (SCFAs), may impact the progression of Alzheimer’s disease.

Research has also demonstrated that SCFAs, produced by gut bacteria, can reduce inflammation, enhance cognitive function, and diminish the likelihood of developing Alzheimer’s disease. That bears repeating: healthy gut bacteria produce chemicals that can boost your cognitive function and stop memory loss. That in and of itself is a great reason to do whatever you can to support healthy gut microbiota. Best of all, it's not that hard.

Short Chain Fatty Acids (SCFAs) Fight Brain Inflammation Like Nobody's Business

SCFAs, such as butyrate, propionate, and acetate, are the primary metabolites generated by the microbiota in the large intestine. They're created through the anaerobic fermentation of indigestible polysaccharides, including dietary fiber and resistant starch. These SCFAs possess anti-inflammatory characteristics and can alter brain functioning, and even stop the development of Alzheimer’s disease.

In one study, mice which were treated with SCFAs through drinking water showed improvements in cognitive performance, supporting the potential benefits of SCFAs for preventing Alzheimer’s disease.

Fortunately, making small, healthy changes to your lifestyle is the first step to support the production of SCFAs and improve the health of your gut.

Lifestyle Factors Affecting Gut Health and Alzheimer's Disease

Lifestyle factors, such as diet, sleep, and exercise, can significantly impact gut health and lower your risk for developing Alzheimer's disease.

Research has shown that a healthy diet, regular exercise, and adequate sleep can support a healthy gut microbiome by reducing inflammation and bolstering immune system function.

Eating A Gut-Boosting Diet

A healthy diet rich in fruits, vegetables, and whole grains can promote a diverse gut microbiome, reducing Alzheimer’s disease risk. This is a diet rich in antioxidants, vitamins, polyphenols, unsaturated fatty acids, fish, whole grains, green leafy and other vegetables, berries, poultry, beans, and nuts.

It's the exact opposite of eating a diet high in saturated and trans fats and low in fruits, vegetables, and whole grains, which has been linked to Alzheimer’s disease.

We write frequently about the link between a healthy diet and brain health. Two recent posts include: Does This Diet Reduce the Risk of Alzheimer's Disease? and Why the MIND Diet is Proven to Cut Alzheimer's Risk in Half.

Sleep and Exercise

Adequate sleep and regular exercise can also contribute to a healthy gut microbiome and help prevent Alzheimer’s disease. Research has shown that low levels of physical activity and poor sleep are associated with an increased risk of Alzheimer’s disease. We've written about the importance of sleep to memory function repeatedly over the years.

Exercise has been found to reduce the risk of developing dementia by approximately 30 percent and has been shown to support a healthy gut microbiome. Furthermore, poor sleep has been linked to abnormal levels of beta-amyloid protein in the brain, which can lead to the amyloid plaques found in the Alzheimer’s brain. We've published many articles on the topic of exercise and memory as well.

Where The Future of Alzheimer's Treatment is Headed

Future research and therapeutic approaches for this memory robbing disease aim to better understand the link between gut bacteria and Alzheimer’s disease. Personalized diets and beneficial microbiota interventions will no doubt one day help modulate gut microbiota to reduce inflammation and stop Alzheimer's disease.

Alzheimer's Gut Microbiome Project

The Alzheimer’s Gut Microbiome Project is an initiative exploring the dynamic role of the gut microbiome in the different stages of Alzheimer's. One of the subprojects of this initiative, led by Dr. Rob Knight, a renowned microbiome researcher and professor at the University of California, San Diego. Dr. Knight aims to examine the effects of a modified Mediterranean diet, a ketogenic diet, and lifestyle modifications on brain health and cognition.

The modified Mediterranean diet is a plant-based diet that emphasizes whole grains, fruits, and vegetables. A ketogenic diet involves consuming a very low amount of carbs and replacing them with fat to help your body burn fat for energy.

Probiotic Therapy

We know supporting the health of the good bacteria in your gut can help protect your memory. But identifying specific gut bacteria and their metabolic pathways involved in Alzheimer’s disease may lead to the development of new ways to prevent or treat the disease.

Probiotics, which are formulations of live, beneficial bacteria, and prebiotics can help keep your body digestion comfortable and healthy and protect against memory loss. We've written about the importance of taking probiotic and prebiotic supplements for years.

That's why Green Valley Natural Solutions formulated Comfort Pro: Premium Probiotic Formula. Once available only in Japan, this unique strain of probiotic, BB-536, is the ONLY probiotic clinically proven in six human studies to improve digestion and alleviate hard stools, constipation and bad bacteria overgrowth... the only probiotic strain with over 110 health studies documenting its health benefits... the most researched probiotic in the world... and the #1 best-selling probiotic in Japan.

Other Interventions

There are also numerous studies showing the benefits of fecal matter transplant (FMT) for improving gut dysbiosis, or an imbalance of bacteria in the digestive tract. This therapeutic strategy involves altering the gut microbiome by introducing fecal matter (stool samples) from a healthy donor into the patient’s gut.

While it sounds pretty unusual, in addition to improving overall digestion, FMT has also been shown to reduce the development of Alzheimer's disease in mouse models (aged mice).

Summary

The intricate relationship between gut bacteria and Alzheimer’s disease holds tremendous potential for the treatment and prevention of this terrible disease.

By beginning to understand the gut-brain axis and the complex relationship between the gut microbiome, lifestyle factors, and Alzheimer’s disease, you can learn to better support your digestion, lower inflammation (inflammatory cytokines) and reduce your risk of developing Alzheimer's disease.

Best of all, you don't have to wait. Those lifestyle changes we just told you about and the addition of a good probiotic formula to your daily nutritional supplement regimen will go a long way to lowering your risk of Alzheimer's disease.

Frequently Asked Questions

• Is Alzheimer's linked to gut bacteria?

Research suggests that the health of the gut microbiome may be an important factor in the development of Alzheimer’s disease and dementia, suggesting a strong link between these illnesses and the health of the gut. Further research is needed to understand the exact relationship between the two and how to better support gut health.

• What gut disorders are linked to Alzheimer's?

Gut disorders such as gastroesophageal reflux disease (GERD), peptic ulcer disease (PUD), gastritis-duodenitis, irritable bowel syndrome, and diverticulosis have been linked to Alzheimer’s Disease.

• What are the potential benefits of short-chain fatty acids (SCFAs) in Alzheimer's disease?

SCFAs have been shown to reduce inflammation, enhance cognitive performance, and diminish the likelihood of developing Alzheimer’s disease, making them potential beneficial supplements for people suffering from Alzheimer’s.

• How can lifestyle factors, such as diet, sleep, and exercise, influence Alzheimer's disease risk?

Living a healthy lifestyle consisting of a balanced diet full of fruits and vegetables, regular exercise, and sufficient sleep can help promote a diverse gut microbiome and reduce inflammation, and reduce the risk of developing Alzheimer’s disease.

• What are some potential therapies and interventions being studied for Alzheimer's disease?

Therapies and interventions being studied for Alzheimer’s disease include identifying good and bad gut bacteria, as well as the role of probiotics, prebiotics, and fecal matter transplant (FMT). These treatments aim to prevent and even treat the disease.