Recent research from Japan suggested that elevated levels of a common oral and gut bacteria, Streptococcus anginosus, may be associated with both increased stroke risk and poorer outcomes in stroke survivors. The preliminary findings were presented at the American Heart Association's International Stroke Conference 2025.
In the study, researchers recruited 250 Japanese participants (mean age = 70, 40% female) and found that S. anginosus was significantly more prevalent in both the saliva and guts of patients who experienced acute strokes compared with controls. After controlling for vascular risk factors, the presence of S. anginosus in the gut was independently associated with a 20% higher risk of stroke, according to a press release from the American Heart Association.
"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. Targeting these specific harmful oral bacteria may help prevent stroke," said lead study author Shuichi Tonomura, MD, of the National Cerebral and Cardiovascular Center in Osaka, Japan.
The 2-year follow-up data revealed that stroke survivors with S. anginosus in their guts experienced significantly higher mortality rates and major cardiovascular events compared with those without the bacteria. Conversely, two other gut bacteria—Anaerostipes hadrus and Bacteroides plebeius—were associated with reduced stroke risk by 18% and 14%, respectively.
"Poor oral health can lead to inflammation and may increase the risk of stroke. The increased levels of S. anginosus found in the guts of patients with recent stroke [are] intriguing, and the fact that levels were linked to increased mortality 2 years after stroke suggests that it may play a role in ongoing stroke risk," noted Louise D. McCullough, MD, PhD, FAHA, who was not involved in the study.
The research involved analyzing oral and gut microbiomes using saliva and stool samples from 200 stroke patients and 50 controls between July 2020 and July 2021. The patients who experienced strokes had been diagnosed within 7 days of the study using brain imaging.
The researchers acknowledged study limitations, including the relatively small sample size and homogeneous Japanese population, which may affect generalizability to other populations. They plan to conduct additional studies in patients with stroke risk factors who have not yet experienced a stroke.
The findings built upon previous research linking another oral bacteria, Streptococcus mutans, to increased risk of cerebral hemorrhage, highlighting the potential importance of oral hygiene in stroke prevention.
The researchers emphasized that maintaining good oral hygiene, including reducing sugar intake and using the appropriate toothpaste, may be essential for targeting these potentially harmful bacteria.
All findings are considered preliminary until published in a peer-reviewed journal.
