A new study suggests that a common bacteria found in the mouth and gut, Streptococcus anginosus, may be linked to a higher risk of stroke and worse recovery outcomes. The findings were presented at the American Stroke Association’s International Stroke Conference 2025.
The Role of Bacteria in Stroke Risk
Our bodies contain trillions of bacteria, known as the microbiome, which help with digestion and other functions. These bacteria exist in the gut and mouth, but when harmful bacteria become too dominant, they can contribute to health problems.
Dr. Shuichi Tonomura, the study’s lead researcher from the National Cerebral and Cardiovascular Center in Osaka, Japan, explained, “If we could quickly detect harmful bacteria in the mouth and gut, we might be able to better predict stroke risk and even prevent strokes by targeting these bacteria.”
What the Study Found
The researchers analyzed the bacteria in the saliva and gut of people who had recently suffered a stroke and compared them to a group of people without stroke. The study included:
- 200 stroke patients (diagnosed within the last seven days)
- 50 non-stroke participants of similar age, undergoing routine medical checkups
The analysis showed that Streptococcus anginosus was significantly more abundant in both the saliva and gut of stroke patients compared to the non-stroke group.
Key Findings
- People with higher levels of Streptococcus anginosus in their gut had a 20% higher chance of stroke, even after adjusting for risk factors like high blood pressure and diabetes.
- Certain beneficial gut bacteria were associated with a lower stroke risk:
- Anaerostipes hadrus reduced stroke risk by 18%
- Bacteroides plebeius reduced stroke risk by 14%
- Over two years of follow-up, stroke survivors with high levels of Streptococcus anginosus in their gut had a significantly higher risk of death and major heart problems.
- This increased risk was not seen in survivors who had higher levels of beneficial bacteria.
Link Between Oral Health and Stroke
These results add to growing evidence that poor oral health may increase stroke risk. In earlier research, the same team found that Streptococcus mutans, another bacteria that causes tooth decay, was linked to a higher risk of brain bleeds(hemorrhagic stroke).
Dr. Tonomura emphasized, “Both Streptococcus mutans and Streptococcus anginosus contribute to tooth decay by producing acids that damage teeth. This highlights the importance of good oral hygiene, reducing sugar intake, and using toothpaste that targets these bacteria.”
Why This Matters
Dr. Louise D. McCullough, a stroke expert from McGovern Medical School in Houston, who was not involved in the study, noted that the increased levels of Streptococcus anginosus found in stroke patients are intriguing. She added that since the bacteria were linked to a higher risk of death and stroke recurrence over two years, they could play a role in ongoing stroke risk.
McCullough also stressed the importance of studying these bacteria in people who have not yet had a stroke but have risk factors. This could help researchers understand how the bacteria contribute to stroke risk and lead to new prevention strategies.
Study Limitations and Future Research
This study was conducted in Japan, with a relatively small sample size (189 stroke patients and 55 non-stroke participants). The microbiome varies based on diet, lifestyle, and geography, so the results may not apply to all populations.
Dr. Tonomura explained, “The microbiome is strongly influenced by lifestyle. In other countries, different bacteria may be the main contributors to stroke risk.”
The researchers now plan to expand their study to include people at risk of stroke to see if these bacteria can be used for early detection and prevention.
What This Means for You
This study reinforces the idea that oral health is linked to stroke risk. Taking care of your teeth and gums—through brushing, flossing, and regular dental checkups—may not only prevent cavities but also help lower your risk of stroke.
More research is needed, but in the future, doctors might be able to predict stroke risk through a simple saliva or stool test, allowing for earlier interventions to reduce stroke chances.
If you care about stroke, please read studies that diets high in flavonoids could help reduce stroke risk, and MIND diet could slow down cognitive decline after stroke.
For more health information, please see recent studies about antioxidants that could help reduce the risk of dementia, and tea and coffee may help lower your risk of stroke, dementia.
The research findings can be found in Stroke.
Copyright © 2025 Knowridge Science Report. All rights reserved.
