The risk factors for atherosclerosis (narrowing or blockage of arteries due to fat deposits) - which can lead to heart attacks and stroke - are well known; they include high blood pressure, obesity, raised cholesterol levels and smoking.

The risk factors for atherosclerosis (narrowing or blockage of arteries due to fat deposits) - which can lead to heart attacks and stroke - are well known; they include high blood pressure, obesity, raised cholesterol levels and smoking. However, the way in which the actual changes in the artery wall come about is not yet clear. Recently, an infection by a bacterium or a virus has been considered to play a significant role. A bacterium called Chlamydia pneumoniae is a principal suspect.

This bacterium occasionally causes pneumonia (hence it's name). However, most of the population has been exposed to the organism, without any obvious symptoms at all. In 1988 a study done in Finland revealed that people with coronary artery disease had a positive blood test for a previous C. pneumoniae infection. Since then, other studies have confirmed that an apparent infection with this bug carries a 2-fold increased risk of heart disease. It's actual presence has been demonstrated the tissue of affected arteries, inside cells showing the typical damage of early atherosclerosis.

In spite of these reports, it's still possible that the organism is merely an innocent bystander. Other infectious candidates have been put forward - Helicobacter pylori - a common cause of stomach ulcer - is one, the human cytomegalovirus (HCMV) is another. Whatever the actual agent, the idea of an infection starting the disease process is now quite popular.

Further support for this comes from a recent study. ¹ Increased amounts of a substance called acute phase C-reactive protein (CRP) in the blood indicate a low-grade infection in the body. High levels carry an increased risk of heart attack and stroke. Overweight and obesity are also known risk factors for these conditions, so that it was interesting to see if overweight people have elevated CRP levels, possibly explaining their increased risk of heart attack or stroke.

Over 16,000 men and women from the USA provided body weight, height, waist and hip measurements, and blood samples for CRP determinations. The body mass index (BMI) for each subject was calculated as the weight (in kilograms) divided by the square of the height (in meters). People with a BMI of 25-30 were classified as "overweight", and those with a BMI over 30 were classified as "obese".

Obese men were twice as likely, and obese women over 6 times as likely, to have raised CRP levels, compared with normal-weight subjects. These results were independent of smoking, age, other chronic diseases etc.

The authors of the study conclude that the results reveal that many overweight and obese persons have an ongoing low-grade inflammation, probably due to an infection. The theory is that fat tissue produces a protein called interleukin 6, which stimulates the production of CRP by the liver.

AS with C. pneumoniae , raised CRP may be just an innocent bystander in the atherosclerosis process - a direct link remains to be established. This has not deterred some physicians from starting a clinical trial of an antibiotic in the patients who have had one heart attack, to try to prevent a second one. It seems likely that we shall soon see the day when we have specially-designed anti-infective or anti-inflammatory drugs to attack the basic process of atherosclerosis. In the meantime, however, there can be no let-up in the vigorous attention paid to the well-known risk factors, such as high blood pressure, smoking, overweight, etc.

Source

Chlamydia pneumoniae and atherosclerosis./ Smoldering arteries? Low-grade inflammation and coronary heart disease. Editorial. A. Shor, JI. Phillips, J. Danesh, JAMA, 1999, vol. 282, pp. 2131--2135

Footnotes

1.

Elevated C-reactive protein levels in overweight and obese adults. M. Visser, LM.  Bouter, GM. McQuillan, et al. , JAMA, 1999, vol. 282, pp. 2071--2073