The researchers at Uppsala and Lund University in Sweden analysed gut bacteria and cardiac imaging among 8,973 participants aged 50 to 65 without previously known heart disease.  They have discovered a link between the levels of certain bacteria living in the gut and coronary atherosclerotic plaques -- which are formed by the build-up of fatty and cholesterol deposits, and constitute a major cause of heart attacks. 

The findings, published in the scientific journal Circulation, revealed that oral bacteria, especially species from the Streptococcus genus, are associated with increased occurrence of atherosclerotic plaques in the small arteries of the heart when present in the gut flora. 

Tove Fall, Professor in Molecular Epidemiology at the Department of Medical Sciences and the SciLifeLab at Uppsala said that species from the  Streptococcus genus are common causes of pneumonia and infections of the throat, skin and heart valves. They also said that they now need to understand whether these bacteria are contributing to atherosclerosis development or not.In this study, scientists investigated the links between the gut microbiota and the build-up of fatty deposits in the arteries of the heart.

“The large number of samples with high-quality data from cardiac imaging and gut flora allowed us to identify novel associations. Among our most significant findings, Streptococcus anginosus and S. oralis subsp. oral were the two strongest ones,” said Sergi Sayols-Baixeras, lead author from Uppsala University.

The research team also found that some of the species linked to the build-up of fatty deposits in heart arteries were linked to the levels of the same species in the mouth. This was measured using faecal and saliva samples. Furthermore, these bacteria were associated with inflammation markers in the blood, even after accounting for differences in diet and medication between the participants who carried the bacteria and those who did not.“We have just started to understand how the human host and the bacterial community in the different compartments of the body affect each other. Our study shows worse cardiovascular health in carriers of streptococci in their gut. We now need to investigate if these bacteria are important players in atherosclerosis development,” said Marju Orho-Melander, Professor of Genetic Epidemiology at Lund University.