Oral bacteria may increase stroke risk: study

Tokyo: Presence of certain bacteria in the mouth may increase the risk of developing hemorrhagic stroke, a new study suggests. In the single hospital study, researchers at the National Cerebral and Cardiovascular Centre in Japan, observed stroke patients to gain a better understanding of the relationship between hemorrhagic stroke and oral bacteria.

Among the patients who experienced intracerebral hemorrhage (ICH), 26 per cent were found to have a specific bacterium in their saliva, cnm-positive Streptococcus mutans.

Among patients with other types of stroke, only 6 per cent tested positive for the bacterium. Strokes are characterised as either ischemic strokes, which involve a blockage of one or more blood vessels supplying the brain, or hemorrhagic strokes, in which blood vessels in the brain rupture, causing bleeding.

Researchers, including those from the University of Louisville in US, also evaluated Magnetic resonance imaging (MRIs) of study subjects for the presence of cerebral microbleeds (CMB), small brain hemorrhages which may cause
dementia and also often underlie ICH.

They found that the number of CMBs was significantly higher in subjects with cnm-positive S mutans than in those without. The S mutans bacteria may bind to blood vessels weakened by age and high blood pressure, causing arterial ruptures in the brain, leading to small or large hemorrhages, researchers
said.

The cnm-negative S mutans bacteria is found in approximately 10 per cent of the general population, and is known to cause dental cavities (tooth decay), they said. "This study shows that oral health is important for brain health. People need to take care of their teeth because it is good for their brain and their heart as well as their teeth," said Robert P Friedland from University of Louisville.

"The study and related work in our labs have shown that oral bacteria are involved in several kinds of stroke, including brain hemorrhages and strokes that lead to
dementia," he said. The findings were published in the journal Scientific Reports.