How Your Gut Microbiome Affects Your Cognitive Health

The gut-brain axis not only influences how we feel day to day: It may also affect how our brains age and function over time, even playing a role in our risk for neurodegenerative diseases such as Alzheimer’s and Parkinson’s.

One of the most important ways the gut influences cognitive health is through its effect on the blood-brain barrier, which protects the brain and spinal cord from harmful substances. Recent research shows that gut ­microbes play a surprising role in keeping the barrier strong and selective.

When researchers compared germ-free mice and mice with healthy gut bacteria, the germ-free mice had increased blood-brain barrier permeability. But when they received either a fecal transplant from healthy mice or supplements of SCFA-producing bacteria, the integrity was restored.

When the blood-brain ­barrier is leaky, harmful molecules and ­immune cells can cross into the brain and trigger neuroinflammation. And a lack of gut ­microbes that produce key metabolites can affect the behavior of ­microglial cells — the immunity ­defense in the central nervous system — leading to excessive synaptic pruning and damage to healthy brain tissue.

Studies show that people with ­Alzheimer’s disease tend to have gut bacterial ­compositions that ­differ from healthy individuals, often including a higher proportion of the proinflammatory Collinsella strain.

Researchers are increasingly looking at whether manipulating the microbiome with diet or probiotic supplements can reduce the risk or affect the progression of neurodegenerative diseases. A 2024 systematic review in the International Journal of General Medicine found that probiotics show promise in helping treat symptoms of Alzheimer’s, Parkinson’s, and multiple sclerosis.