New research suggests possible link between higher stroke risk and common mouth and gut bacteria

New research indicates a possible connection between Streptococcus anginosus, a common type of bacteria found in the mouth and gut, and an increased risk for stroke.

Common mouth and gut bacteria may increase stroke risk

Results from a study featured at the 2025 American Stroke Association International Stroke Conference revealed the presence of S. anginosus in recent stroke survivors in Japan. Data showed that even after a two-year follow up, stroke patients with increased levels of this bacterium were more likely to die or suffer a major cardiovascular event than those with lower levels of S. anginosus.¹

Furthermore, this bacterium was independently associated with 20% higher odds of suffering stroke after controlling for vascular risk factors, while a beneficial gut bacterium was associated with a drop in risk by 18%.¹

S. anginosus can cause tooth decay because the acids it produces are strong enough to break down enamel. Maintaining a proper oral hygiene routine, decreasing sugar intake, and using toothpastes that target this bacterium can help prevent tooth decay-and, perhaps, a stroke.

According to Louise D. McCullough, chief of neurology at Memorial Hermann Hospital-Texas Medical Center and co-director of UTHealth Neurosciences, "Poor oral health can lead to inflammation and may increase the risk of stroke. The increased levels of S. anginosus found in the gut of patients with recent stroke is intriguing, and the fact that levels were linked to increased mortality two years after stroke suggests that it may play a role in ongoing stroke risk."¹

More data needed

She also noted that more studies with larger sample sizes are needed to definitively link this bacterium to a higher risk for stroke. The initial study only consisted of 250 people (189 stroke patients and 55 non-stroke participants). The oral and gut microbiomes of these participants were studied through saliva and stool samples collected from July of 2020 to July of 2021.¹

Shuichi Tonomura, lead author of the study and staff physician in the department of neurology at the Osaka's National Cerebral and Cardiovascular Center, said "In the future, if there was a quick test to detect harmful bacteria in the mouth and gut, we could use the information to help calculate stroke risk ... the oral and gut microbiome is strongly affected by lifestyle. Other bacteria may be main players in stroke in other countries."¹

Researchers intend to collect data from people who have not had a stroke but demonstrate increased risk factors for one. McCullough and her team believe doing so can help elucidate the relationship between S. anginosus and stroke risk-and as a result, improve prevention strategies.

Reference

1. A common mouth and gut bacteria may be linked with increased stroke risk. Newsroom. January 30, 2025. https://newsroom.heart.org/news/a-common-mouth-and-gut-bacteria-may-be-linked-with-increased-stroke-risk