Alzheimer's disease (AD) is the most common cause of dementia – a gradual decline in memory, thinking, behavior, and social skills. About 6.5 million individuals in the United States age 65 and older live with AD.1 

Although there isn’t a cure for Alzheimer’s, research continues to try to unravel what causes the disease in hopes of developing an effective treatment. Over the past decade, studies have taken a closer look at the gut microbiome and its role in AD development. Current research is examining whether altering the microbes that live in the gut can prevent, halt, or even reverse disease progression.   

The gut-brain connection

The lining of your gut, like every surface of your body, is covered in microscopic organisms (microbiota) – namely bacteria, fungi, viruses, and protozoans. Collectively, they create an ecosystem called the microbiome.

The microbiome is responsible for helping the body maintain stability (homeostasis) and ward off disease. In return, the human body provides the microbiota with the nourishment they need to survive. In general, a healthy gut microbiome consists of a rich diversity of microorganisms. But if this system is out of balance, or there’s an overgrowth of harmful bacteria inside the gut, then the risk for a number of diseases is higher.2-4

For a long time, it was believed that the brain didn’t have a connection to the gut. However, recent evidence shows that gut microorganisms are part of a two-way communication system, attributable primarily to the body’s longest cranial nerve, the vagus nerve. The vagus nerve links the intestines and the brain, known as the gut-brain axis. What happens in the gut appears to influence the brain and vice versa.2 

It's now believed that the inhabitants of the gut microbiome play a role in regulating neuroinflammation. Neuroinflammation is the inflammatory response within the central nervous system (brain and spinal cord) that is linked to the development and progression of various neurological diseases, such as Alzheimer’s.2,5 

Changes to the gut microbiome might negatively impact the central nervous system’s immune response to inflammation. These changes affect how well the blood-brain barrier works – the tightly spaced cells that let beneficial substances into the brain while keeping out the harmful ones.2,5 

Recent studies show that individuals with AD have altered gut microbiomes – less diversity, more pro-inflammatory microorganisms, and fewer anti-inflammatory ones – compared to those without the disease. It’s unclear, however, if AD creates an imbalance in the gut microbiome or if an unhealthy mix of microbes plays a role in developing the disease. Research on animals shows that manipulating the gut microbiome can impact neuroinflammation. However, more study is needed since it has yet to be proven in human studies.2,5 

Be good to your gut

While research continues to connect the dots between AD and the gut microbiome, you can take steps to nourish your gut, which will benefit your overall health. 

What you feed your microbiome has a significant impact on its health and function. The healthier it is, the healthier you are. The key to a healthy microbiome is nourishing a balance among the nearly 1,000 different species of bacteria in your gut. There are two ways to maintain this balance – helping the microbes already there to flourish by giving them the food they need (prebiotics) and adding living microbes directly to your body (probiotics):3,4

  1. Prebiotics: Foods like fruits, vegetables, whole grains, and beans contain fiber – which serve as food for the bacteria living in your gut. 
  2. Probiotics: Foods that contain beneficial bacteria include kefir, kimchi, kombucha, miso, sauerkraut, sourdough, tempeh, and yogurt with live cultures.

What you don’t put into your body is also crucial. Avoid a diet high in fast food, sugar, processed foods, and excessive alcohol, all of which can decrease gut health.4

To learn more things you can do to keep your gut microbiome healthy, read How Does the Gut Microbiota Develop and Change Throughout Life? 

Tips for reducing the risk for Alzheimer’s disease

An abundance of evidence now links living a heart-healthy lifestyle with a reduced risk of developing Alzheimer's and other types of dementia. Although it's too early to claim these factors can prevent dementia, they can help keep your brain healthy. 

Tactics to follow a heart-healthy lifestyle include:1,5,6

  • Engage in aerobic exercise and strength training regularly. Get at least 150 minutes of moderate aerobic activity or 75 minutes of vigorous aerobic activity weekly, or a combination of moderate and vigorous activity. At least 300 minutes weekly is recommended to provide an even greater health benefit. But even small amounts of physical activity are helpful. Do strength training exercises for all major muscle groups at least twice weekly.
  • Eat a diet of fresh produce, healthy oils, and foods low in saturated fat. Some research suggests that eating the plant-focused Mediterranean diet is linked to improved memory, increased grey matter in the brain (responsible for activities such as processing information), and reduced AD lesions in the brain.
  • Follow treatment guidelines to manage high blood pressure, diabetes, and high cholesterol.
  • Stop smoking or ask your health-care professional for help to quit.

Other studies show that staying engaged mentally and socially is linked to preserved thinking skills later in life and a lower risk of AD. This includes going to social events, reading, dancing, playing board games, creating art, playing an instrument, and other activities.1

Until there’s a cure, it’s nice to know there are things you can do that reduce your risk for developing Alzheimer’s disease. Taking good care of the microbes that inhabit your gut is likely one of them.  

A word from Thorne

A healthy diet including prebiotic fiber and fermented probiotic foods can be supplemented with prebiotic and probiotic supplements. And you can see how your own microbiome stacks up by taking an easy, at-home Gut Health Test.

References

  1. Alzheimer’s disease. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/alzheimers-disease/symptoms-causes/syc-20350447. [Accessed March 29, 2023]
  2. Varesi A, Pierella E, Romeo M, et al. The potential role of gut microbiota in Alzheimer's disease: from diagnosis to treatment. Nutrients 2022;14(3):668. 
  3. Prebiotics, probiotics, and your health. Mayo Clinic. https://www.mayoclinic.org/prebiotics-probiotics-and-your-health/art-20390058. [Accessed March 29, 2023]
  4. Building a healthy gut microbiome. Mayo Clinic Connect. https://connect.mayoclinic.org/blog/weight-management-1/newsfeed-post/building-a-healthy-gut-microbiome/. [Accessed March 29, 2023]
  5. Chandra S, Sisodia SS, Vassar RJ. The gut microbiome in Alzheimer's disease: what we know and what remains to be explored. Mol Neurodegener 2023;18(1):9. 
  6. How much should the average adult exercise every day? Mayo Clinic. https://www.mayoclinic.org/healthy-lifestyle/fitness/expert-answers/exercise/faq-20057916. [Accessed March 29, 2023]