As we grow older, the bacteria in our mouths could play an unexpected role in how well our brains work. A recent study has found that some types of oral bacteria are linked to better memory and thinking skills, while others may raise the risk of cognitive decline.
This discovery adds to a growing body of research showing how the tiny organisms in our bodies—especially in our mouths and guts—might influence brain health as we age.
Around 15% of older adults experience mild cognitive impairment, or MCI. This condition includes memory problems or trouble with thinking that go beyond normal aging but are not yet severe enough to be classified as dementia. MCI is also known to be the biggest risk factor for developing Alzheimer’s disease.
Previous research has already found a connection between gum disease (also called periodontitis) and worsening brain function. Scientists believe the bacteria involved in gum disease might not just damage the mouth—they could also affect the brain.
There are two main ways this might happen. First, harmful bacteria in the mouth could enter the bloodstream and travel to the brain, where they might trigger inflammation or directly damage brain cells.
Second, these bacteria might outcompete and replace helpful bacteria in the mouth—particularly those that help convert dietary nitrate into nitric oxide. Nitric oxide is a gas that plays a critical role in brain function, especially in supporting the brain’s ability to form new connections and store memories.
The new study, published in PNAS Nexus, was led by Anni Vanhatalo and her team. They studied the oral microbiomes—the mix of bacteria living in the mouth—of 115 people. Among them, 55 had mild cognitive impairment, and some carried a gene called APOE4, which increases the risk of developing Alzheimer’s disease.
The researchers found some surprising patterns. One type of bacteria, from a group called Neisseria, was linked to better brain function.
People with more Neisseria in their mouths tended to do better on tasks involving memory, attention, and decision-making—especially those with MCI. Among healthy individuals, higher levels of Neisseria were connected to better working memory.
On the other hand, people who had more bacteria from the Porphyromonas group were more likely to have MCI. This group includes Porphyromonas gingivalis, which has been linked to gum disease and brain problems in earlier research.
Another type of bacteria, Prevotella intermedia, was found more often in people with the APOE4 gene, suggesting a possible link between this microbe and higher genetic risk for Alzheimer’s.
Importantly, the study also points out that our diets can shape the bacterial balance in our mouths. Diets rich in natural nitrates—such as the Mediterranean diet or the DASH diet (Dietary Approaches to Stop Hypertension)—may support the growth of bacteria like Neisseria that are linked to better brain outcomes.
These diets include lots of vegetables, fruits, whole grains, and leafy greens, which are known sources of natural nitrates.
Based on these findings, the researchers believe that dietary changes or targeted use of prebiotics—substances that support the growth of good bacteria—could help improve or protect brain function, especially in older adults.
In summary, this study adds to growing evidence that the bacteria living in our mouths may have a meaningful impact on our brain health.
While more research is needed to understand exactly how these bacteria affect memory and thinking, the results suggest that taking care of your mouth through good oral hygiene and healthy eating may do more than just protect your teeth—it could also help protect your mind as you age.
If you care about brain health, please read studies about how the Mediterranean diet could protect your brain health, and Omega-3 fats and carotenoid supplements could improve memory.
For more information about brain health, please see recent studies about antioxidants that could help reduce dementia risk, and higher magnesium intake could help benefit brain health.
The research findings can be found in PNAS Nexus.
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