Common mouth bacteria linked to heart disease in new Finnish study

A Finnish study suggests a common mouth bacterium may be linked to heart disease, the world’s leading cause of death. Researchers analyzed fatty deposits, or plaques, that build up in arteries and restrict blood flow to the heart, focusing on samples from more than 100 people who died of a heart attack and about 100 others who underwent plaque-removal surgery.

They detected DNA from Viridians streptococci, a bacterium normally found in the mouth and digestive tract, in more than 40% of plaque samples across both groups. In the study, the bacteria largely existed as a biofilm—a community of organisms embedded in an extracellular matrix—inside the arterial walls where they can evade immune detection. The researchers note that biofilms can remain dormant and hard to spot, but may become activated and contribute to inflammation and clotting under certain conditions.

The presence of Viridians streptococci inside plaques underscores a possible link between oral health and cardiovascular risk, particularly for people with immune suppression or chronic illness, in which bacteria may escape the protective biofilm and influence disease progression. When infected tissue breaks away from a heart valve, bacteria can travel through the bloodstream and lodge in the coronary arteries, potentially triggering a heart attack.

Based on the results, researchers are urging Americans to maintain proper oral hygiene—brushing and flossing teeth twice a day and staying current with dental checkups—to reduce the oral burden of Viridans streptococci. The study, published last month in the Journal of the American Heart Association, analyzed coronary plaque samples from 121 people who suffered sudden cardiac death and 96 who had an endarterectomy, a procedure to remove plaque from the inner lining of an artery. The average age in the sudden-death group was 63, and nearly three-quarters were men; their body mass index (BMI) averaged 30, indicating obesity. In the endarterectomy group, the average age was 69, 72% were men, and BMI averaged 27.

The researchers found bacteria in 66% of plaques from the deceased group and 58% from the surgery group. Viridans streptococci were the most common bacteria in both groups, present in 42% of plaques among those who died and 43% among the surgical patients. In normal, unobstructed arteries, bacteria were less prevalent. Dr. Pekka J. Karhunen, study author and professor at Tampere University, said the findings point to a biofilm consisting of many bacteria in atherosclerotic plaques and suggested that calculus on dental biofilms on teeth might relate to calcification in coronary arteries.

“Oral viridans group Streptococci are known to act as early colonizers in the buildup of the dental biofilm known as dental plaque,” Karhunen said. “This signals that the streptococci may not be there alone—it is possible that there is a biofilm composed of many bacteria.” He described bacteria within the biofilm as largely dormant and protected, but noted that infections or other triggers could activate the biofilm and cause the bacteria to spread to the plaque, promoting inflammation and clot formation. The researchers cautioned that the findings are not definitive but are exploring how to reduce biofilm formation and whether vaccines against bacterial-induced thrombosis might be possible in the future.

Dr. Elizabeth Klodas, chief medical officer and founder of Step One Foods, told Prevention that the study highlights the interconnectedness of bodily systems. She stressed that regular dental checkups, along with brushing and flossing, can be beneficial not only for oral health but potentially for heart health as well.

Heart disease remains a leading public health challenge. In the United States, cardiovascular disease affects about one in three adults—roughly 83 million people—according to health authorities. The burden is expected to grow, with projections suggesting that by 2050 more than 60 percent of Americans could have some form of heart disease. Cardiovascular disease accounts for about one in three deaths in the United States, underscoring the ongoing urgency of prevention, early detection, and treatment.

The new study’s authors emphasize that their work is a starting point for understanding how oral bacteria may interact with arterial disease. They are pursuing further research into how oral hygiene might influence plaque biology and whether targeted interventions could reduce the risk of bacterial-induced thrombosis in vulnerable individuals.