The Connection Between the Gut-Brain Axis and Dementia

the Gut-Brain Axis and Dementia
July 14, 2025
  • Ibukun Odebode

The gut-brain axis is the way your gut (digestive system) and brain communicate with each other. It’s a 2 way system meaning the brain can affect the gut and vice versa. This connection plays a role in things like digestion, emotions, memory, and motivation. The brain and gut send signals through nerves like the vagus nerve and hormones like cortisol. The trillions of bacteria and other microorganisms in your digestive system can also produce substances to impact mood and brain function.

What is the impact on brain health?

The gut-brain axis helps to keep balance in our body. Disruptions to this communication system can increase the risk of dementia in many different ways:

Chronic Inflammation2,3

Gut dysbiosis, an imbalance of the gut microbiome, can lead to an overgrowth of pro-inflammatory bacteria. These bacteria can cause inflammation by releasing inflammatory molecules into the bloodstream. Chronic inflammation is a risk factor for dementia and Alzheimer’s disease because it can damage blood vessels in the brain.

Decreased protection of the brain3,4

Good bacteria in your digestive system produce short-chain fatty acids that help your immune cells work properly and protect your brain. These cells also help to keep the blood-brain barrier strong. This barrier acts like a protective shield that helps keep harmful substances out of the brain. An imbalance in this system can cause a variety of problems. When it is underactivated with a reduced amount of short-chain fatty acids, it can lead to reduced protection of the brain causing issues in memory and thinking. On the other hand, when it is too active, it can damage brain cells, which is often seen in conditions like Alzheimer’s disease.

Release of neurotoxins5,6

Some types of gut bacteria can produce toxins that harm the brain. When these neurotoxins build up in the body, they’ve been linked to hardening of the arteries, which can reduce blood flow to the brain and speed up cognitive decline. These toxins can also cause inflammation, further damaging brain cells and increasing the risk of dementia.

Decrease brain plasticity7

Dysbiosis can also reduce the brain’s ability to adapt and form new connections in a process called brain plasticity. This process is really important for learning and memory. When disrupted, it can speed up cognitive decline and increase the risk of dementia.

Who does it affect3,8

Certain populations are more at risk of imbalances in the gut microbiome:

  • Older adults

As you age, your gut microbiome becomes less diverse making it more prone to imbalances. This can lead to more inflammation and increase the risk of damaging brain cells.

  • People with poor diets

Diet has a strong impact on the gut microbiome. Diets low in fiber and high in processed foods can disrupt the balance of gut bacteria

  • People with chronic illnesses

Chronic illnesses like diabetes, obesity, and GI disorders like IBS also negatively affect the gut-brain axis, raising the risk of dementia

How to maintain a healthy gut-brain connection9,10,11

There are many ways to help maintain a healthy gut-brain connection. These include:

  • Eating a diverse, fiber-rich diet

Whole, plant-based foods like vegetables, fruits, whole grains, and legumes are full of fibre which feeds the good gut bacteria. These bacteria also produce helpful substances that support brain health.

  • Probiotics and fermented foods

Foods with live cultures like yogurt, kefir, sauerkraut and kimchi help to maintain a balanced gut microbiome.

  • Limit processed food

Ultraprocessed foods, added sugars and artificial sweeteners can disrupt gut bacteria and increase inflammation which negatively impacts the gut-brain axis

  • Manage stress and prioritize sleep

Chronic stress and poor sleep can alter the gut microbiome and reduce beneficial bacteria. Poor sleep can also increase risk of cognitive and mood problems.

Signs of an imbalanced gut12,13

Gut dysbiosis happens when the bacteria in your digestive system is disrupted. It can affect your digestion, immune system, mood, and increase risk of cognitive decline. You might have an imbalanced gut if you have:

  • Chronic digestive issues (bloating, gas, constipation, heartburn)
  • Trouble concentrating or low mental energy
  • Sudden, unexplained food cravings or sensitivities
  • New skin issues (eczema, acne, rashes)
  • Frequent illness or weakened immune system
  • Poor or irregular sleep

References:

  1. Carabotti, M., Scirocco, A., Maselli, M. A., & Severi, C. (2015). The gut-brain axis: interactions between enteric microbiota, central and enteric nervous systems. Annals of gastroenterology, 28(2), 203–209. https://pmc.ncbi.nlm.nih.gov/articles/PMC4367209/
  2. Guildford, A. (2022, January 27). Dementia: Do gut bacteria play a role? Medical News Today. Retrieved July 7, 2025, from https://www.medicalnewstoday.com/articles/does-the-gut-play-a-role-in-dementia-here-is-the-evidence
  3. Seo, Do., Holtzman, D.M. Current understanding of the Alzheimer’s disease-associated microbiome and therapeutic strategies. Exp Mol Med 56, 86–94 (2024). https://doi.org/10.1038/s12276-023-01146-2
  4. L., K., Ng, T. K., Wee, H. N., & Ching, J. (2023). Gut-brain axis through the lens of gut microbiota and their relationships with alzheimer’s disease pathology: Review and recommendations. Mechanisms of Ageing and Development, 211, 111787. https://doi.org/10.1016/j.mad.2023.111787
  5. Bhandari, T. (2023). Gut bacteria affect brain health, mouse study shows – WashU Medicine. WashU Medicine. Retrieved July 7, 2025, from https://medicine.washu.edu/news/gut-bacteria-affect-brain-health-mouse-study-shows/
  6. Saji, N., Niida, S., Murotani, K. et al. Analysis of the relationship between the gut microbiome and dementia: a cross-sectional study conducted in Japan. Sci Rep 9, 1008 (2019). https://doi.org/10.1038/s41598-018-38218-7
  7. L., K., Ng, T. K., Wee, H. N., & Ching, J. (2023). Gut-brain axis through the lens of gut microbiota and their relationships with alzheimer’s disease pathology: Review and recommendations. Mechanisms of Ageing and Development, 211, 111787. https://doi.org/10.1016/j.mad.2023.111787
  8. Kowalski, K., & Mulak, A. (2019). Brain-Gut-Microbiota Axis in Alzheimer’s Disease. Journal of neurogastroenterology and motility, 25(1), 48–60. https://doi.org/10.5056/jnm18087
  9. Shetty, M. (2024, April 8). More Than a Gut Feeling: How Your Microbiome Affects Your Mood. Stanford Center on Longevity. Retrieved July 7, 2025, from https://longevity.stanford.edu/lifestyle/2024/04/08/more-than-a-gut-feeling-how-your-microbiome-affects-your-mood/
  10. Rosenbloom, C. (2024, April 21). Nurturing your gut-brain connection for whole body health. Heart and Stroke Foundation of Canada. Retrieved July 7, 2025, from https://www.heartandstroke.ca/articles/nurturing-your-gut-brain-connection-for-whole-body-health
  11. Champion, C. (2023, October 23). You are what you eat: Diet may affect your mood and brain function. uclahealth.org. Retrieved July 7, 2025, from https://www.uclahealth.org/news/article/you-are-what-you-eat-diet-may-affect-your-mood-and-brain
  12. DeCesaris, L. (2025, January 14). What Is Gut Dysbiosis? 7 Signs To Watch For. rupahealth.com. Retrieved July 7, 2025, from https://www.rupahealth.com/post/how-your-gut-bacteria-affects-your-overall-health
  13. Sethi, S., Robertson, R., & Kubala, J. (n.d.). Dysbiosis: Test, Treatment, and More. Healthline. Retrieved July 7, 2025, from https://www.healthline.com/health/digestive-health/dysbiosis