A new study found that after several years of this low-level inflammation, men are three times as likely to suffer heart attacks and twice as likely to have strokes. The inflammation is so subtle that it shows up only on blood tests, and seemingly normal levels may be hazardous.
Earlier studies have found signs of this inflammation at the time of a heart attack. The new work is the first to show that it simmers away while men are still outwardly healthy, apparently contributing insidiously to clogged arteries.
Why this micro-inflammation, as doctors call it, happens is still a mystery. However, a leading theory is that chronic infection with common germs might be the cause.
If so, the study raises the possibility that antibiotics and vaccines, along with stronger anti-inflammatory drugs, might someday be added to the medicines routinely used to treat heart disease.
The new research also helps explain why aspirin is so good for the heart. For years, experts thought aspirin's main benefit was its interference with blood clotting. But the new study suggests it also works by fighting inflammation inside the blood vessels.
Heart attacks strike when fatty deposits build up in the arteries. When one of the deposits, called plaque, suddenly breaks open, blood clots form and choke off the supply of blood to the heart muscle.
While too much cholesterol in the bloodstream clearly is a major underlying cause of heart trouble, doctors have long suspected that other factors must also be at play.
"The ability of doctors to predict who is at risk of cardiovascular disease has come a long way. But about half of those who get heart attacks or strokes have normal cholesterol levels," noted Dr. Paul Ridker of Brigham and Women's Hospital in Boston.
The theory is this: An infection attracts disease-fighting white blood cells, called monocytes, to the blood vessel walls. These, in turn, release a host of chemicals that can stimulate the growth of smooth muscle cells and contribute to the development of clogging deposits.
Ridkler and colleagues studied male doctors who had taken part in a large aspirin study that began in 1982. They looked at levels of C-reactive protein, a sign of inflammation, in 543 who went on to suffer heart attacks, strokes or vein clots after eight years of follow-up and an equal number who stayed healthy.
The men were divided into four categories, depending on their levels of this protein. Those in the top quarter had twice the risk of stroke and three times the risk of heart attacks of those in the bottom quarter.
Ridker said this makes checking the level of C-reactive protein about as accurate as measuring the ratio of total cholesterol to high-density lipoprotein cholesterol. That's currently the most sensitive means doctors have of predicting a heart attack.
Earlier results from the same study found that taking aspirin reduces the risk of a heart attack by 44 percent. However, the latest analysis shows that those with high levels of C-reactive protein benefit most. Their risk fell 55 percent if they took aspirin, while aspirin had little effect on those with low levels of the protein.
"There is no question that the inflammatory process in vessel walls is very important to the progression of atherosclerosis," the dangerous narrowing of the arteries. "The question is what triggers it," said Dr. L. Maximilian Buja, dean of the University of Texas-Houston Medical School.
While the latest study can't answer that question, some doctors think a germ might be involved. One of the leading candidates is Chlamydia pneumoniae. Unlike its cousin that causes venereal disease, this common microbe is frequently involved in pneumonia. People with recent infections seem especially likely to suffer heart attacks, and the bacteria have been found inside the buildups in heart arteries.