MINNEAPOLIS, MINNESOTA. Chronic infections, including periodontal (gum) infections, have previously been associated with cardiovascular disease, a finding supported by links between long-term infections and increased markers of inflammation. Until now, the relationship between periodontal infections and cardiovascular disease has been studied through indirect measures, so researchers from the University of Minnesota decided to investigate the microbiology of periodontal infection. The work forms part of their Oral Infections and Vascular Disease Epidemiology Study (INVEST), which was devised to examine periodontal infection, atherosclerosis (hardening of the arteries), and its related diseases such as stroke and heart attack.
The team took 4561 plaque samples from the gums of 657 healthy participants (approximately seven per mouth), and used DNA analysis to assess the samples for periodontal bacteria. The participants' cardiovascular risk factors were also measured and age, ethnicity, gender, education, body mass index, smoking, diabetes, systolic blood pressure, and cholesterol measurements were taken into account. Also measured were levels of C-reactive protein - a marker of inflammation often used to predict cardiovascular disease risk.
Results showed that greater overall levels of periodontal bacteria were linked to increased carotid artery intima-media thickness (IMT) – degree of atherosclerosis in the main artery of the upper arm. When grouping the samples into thirds, IMT thickness was 0.84 millimeters in the group with the lightest bacterial load and 0.88 mm in the group with the greatest bacterial load. A difference of 0.03 mm is associated with a 15 mm Hg increase in systolic blood pressure, or a doubled risk of heart attack. The researchers discovered that the link was solely due to etiologic bacteria - causally associated to periodontal disease - and furthermore, levels of periodontal bacteria were unrelated to measures of C-reactive protein. White blood cell counts increased significantly with both etiologic bacterial load and IMT thickness, suggesting a direct role of certain infections.
The authors conclude that they have shown clear evidence of an independent relationship between
periodontal bacteria and atherosclerosis, which is unrelated to levels of C-reactive protein. The findings add
to the evidence that oral infections can lead to cardiovascular disease by accelerating atherosclerosis, and
could be relevant to public health if confirmed by prospective studies.