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More Evidence of Inflammation's Role in Heart Disease

Even infection can have inflammatory effect on blood vessels, research finds

WEDNESDAY, Dec. 15, 2004 (HealthDayNews) -- Two studies an ocean apart illustrate the growing importance of inflammation as a contributor to heart attack, stroke and other cardiovascular diseases.

In the United States, researchers at the Harvard School of Public Health report that blood levels of C-reactive protein, a molecular marker of inflammation, rank with cholesterol levels as indicators of future coronary heart disease.

And in England, researchers at the London School of Hygiene and Tropical Medicine report that an ordinary infection -- such as the flu -- may raise the risk of heart attack or stroke over the next few days because of an inflammatory effect on blood vessels.

Both studies appear in the Dec. 16 issue of the New England Journal of Medicine.

Inflammation is the process by which the body responds to injury or infection. Laboratory evidence and results from clinical and population studies suggest that inflammation is important in atherosclerosis, the process by which fatty deposits build up in the lining of arteries, according to the American Heart Association.

The British study was undertaken because inflammation is known to play a long-term role in cardiovascular disease, said study author Liam Smeeth, a senior lecturer in epidemiology.

The idea that an infection could have an immediate damaging effect on the endothelium, the delicate lining of the blood vessels, came from laboratory work done by Dr. Patrick Valliance of University College London, Smeeth said. So, the British researchers looked at the record of infections reported by nearly 40,000 people who had had a stroke or heart attack.

"The risk of both events were substantially higher after a diagnosis of systemic respiratory tract infection and were highest in the first three days," the researchers reported. Urinary tract infections also raised the risk, but to a lesser extent, the study found.

There was one bit of good news: Getting vaccinated against influenza, tetanus or pneumonia did not increase the risk of a cardiovascular event, as the researchers suspected might happen.

"Either it [vaccination] produces no inflammatory effect or it has an effect only in a subgroup of people," Smeeth said. "That is reassuring news."

The Harvard report used data from two studies that have been following more than 120,000 health professionals, male and female, for many years. They underwent a large number of blood tests, including markers of inflammation, at the start of the study. The researchers looked at those levels in the 239 women and 265 men who had heart attacks or died of heart disease over the next six to eight years.

A high level of C-reactive protein -- more than 3 milligrams per liter of blood -- increased the risk of such an event by nearly 70 percent, compared to a reading lower than 1 milligram per liter, after adjusting for the presence of two other risk factors, diabetes and high blood pressure, the researchers found.

Blood levels of cholesterol and other lipids were stronger predictors of trouble, but "the level of C-reactive protein remained a significant contributor to the prediction of coronary heart disease," they reported.

Right now, measuring blood levels of C-reactive protein are "supplementary to measuring traditional risk factors," such as cholesterol, blood pressure and obesity, said Dr. Nieca Goldberg, chief of women's cardiac care at Lenox Hill Hospital in New York City, and a spokeswoman for the American Heart Association.

"There are individuals in whom we would want to measure C-reactive protein, such as those who have coronary disease but no other risk factors and those at borderline or intermediate risk," she said. "But we are not at the point where we would use it as the sole determinant of risk."

Jennifer K. Pai, a research associate at the Harvard School of Public Health and lead author of the journal report, said she agreed with that assessment.

"Using it [C-reactive protein levels] in conjunction with these other risk factors probably would be best," Pai said.

More information

The American Heart Association has more on the role of C-reactive protein and inflammation in coronary disease.

SOURCES: Liam Smeeth, Ph.D, senior lecturer, epidemiology, London School of Hygiene and Tropical Medicine, England; Nieca Goldberg, M.D., chief, women's cardiac care, Lenox Hill Hospital, New York City; Jennifer K. Pai, Sc.D, research associate, Harvard School of Public Health, Boston; Dec. 16, 2004, New England Journal of Medicine
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