DALLAS, Oct. 14 - - If your blood levels of "good" cholesterol are low and you already have heart disease, you may be at increased risk of having a stroke, according to a report published today in the American Heart Association journal Stroke.
Millions of people have these characteristics, and their risk of suffering a stroke, the nation's No. 1 cause of disability, may be increased twofold, say scientists who wrote the report. They describe it as the first to document that atherosclerosis can develop in multiple sites in the body in individuals with low levels of "good" cholesterol (HDL or high-density lipoprotein) and normal amounts of the "bad" low-density lipoprotein (LDL).
Atherosclerosis, in which blood vessels become obstructed with plaque filled with "bad" cholesterol, can occur in the blood vessels to the heart, the carotid arteries (the vessels in the neck that transport blood to the brain), and peripheral blood vessels in the legs.
"It's important to identify those individuals who have atherosclerosis in more than one site, so that we can intervene earlier and perhaps reduce their risk of both coronary heart disease and stroke," says Timothy J. Wilt, M.D., M.P.H., associate professor of medicine at the Minneapolis VA Medical Center and the University of Minnesota.
More than 60 percent of the 202 men in the study had early tell-tale signs of atherosclerosis in their neck arteries. Obstructions in these vessels can block blood flow to the brain, triggering a stroke. Thickening of artery walls was found in nearly 90 percent of the men.
Because atherosclerosis had been diagnosed only in the blood vessels to their heart, the men may not have been receiving the best drug therapy or were not advised to make lifestyle changes that would have helped reduce their risk for heart attack and stroke, Wilt says. Earlier detection and more intense focus on reducing risk factors -- smoking, sedentary lifestyle, and a diet high in fat, particularly saturated fat -- can improve quality of life and save lives, he says.
Despite recent success with the new cholesterol-lowering drugs, "many patients being treated for heart disease are not yet on them," he says. "Right now the focus is on whether LDL is too high, and if so, we treat it. But we don't know what to do if the HDL is low."
Early signs of atherosclerosis were detected in the men's carotid arteries by an imaging technique called B-mode ultrasound, which makes X-ray pictures by bouncing sound waves off tissues, Wilt explains. This method was used to examine the 202 males as part of a larger study, the Department of Veterans Affairs HDL Intervention Study, to determine whether a drug, gemfibrozil, can raise HDL while reducing triglycerides, the main type of blood fat.
Already, there's one favorable finding on gemfibrozil. Finnish researchers reported last week (Oct. 7) in the American Heart Association journal Circulation that in men with low levels of "good" cholesterol, the drug retarded the progression of atherosclerosis in the blood vessels to the heart and and in the vein grafts surgically attached to vessels to bypass obstructions caused by atherosclerosis. The study of 395 men is the largest of its type to show that the drug can slow the advance of heart disease, according to the scientists.
In the study reported today in Stroke, ultrasound exams found thickening of the inner and middle layers of the lining of the blood vessel -- seemingly small changes that have large and ominous implications. Previous research has equated thickened vessel to reduced quality and length of life, possibly accounting for 20 to 40 percent increased risk of stroke, Wilt notes.
Combining the new findings with results of the earlier studies, he estimates: "For every 3 tenths of a millimeter increase in wall thickness, there's a 20 percent increase in stroke risk."
Wilt and his colleagues also compared the thickness of the vessel lining in the men with heart disease and males who were free of the disease. Both groups of men were similar in age, gender and racial characteristics. With an average age 64 and with most being Caucasian, the men with heart disease had "good" cholesterol levels of 32 milligrams per deciliter (mg/dl) of blood. "Bad" cholesterol was 113 mg/dl and total cholesterol levels averaged 174 mg/dl. These levels of total and "bad" cholesterol are in acceptable ranges but the "good" cholesterol levels are rated as low. HDL levels are considered below average if they are 35 mg/dl or less.
The "good cholesterol" helps to clear artery-clogging fatty substances from the blood. "Bad" cholesterol deposits its lethal load in the interior walls of blood vessels, narrowing the passage for blood flow, thereby starving the heart and oxygen of blood. This leads to heart attack and stroke.
In addition to low "good" cholesterol, factors associated with vessel thickness were older age; a history of atherosclerosis in leg blood vessels; smoking; high blood pressure; and evidence of carotid artery "stiffness." When vessels become stiff, the heart has to work harder to pump blood through the body. This increase in blood vessel stiffness is regarded as an early step in atherosclerosis.
Other co-authors of the Minneapolis study with Wilt are Hanna B. Rubins, M.D., M.P.H.; Sander J. Robins, M.D.; Ward A. Riley, Ph.D.; Dorothea Collins, Sc.D.; Marshall Elam, M.D., Ph.D.; Gale Rutan, M.D., M.P.H.; and James W. Anderson, M.D.
Stroke and Circulation are scientific journals published by the American Heart Association, which has its national headquarters in Dallas.
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Media advisory: Dr. Wilt can be reached in Minneapolis by calling (612) 725-2158. Reporters may call (214) 706-1173 for copies of the reports. (Please do not publish telephone numbers.)