Less protection from aspirin found in 69% of people with high cholesterol
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A new study finds that two in three people with high cholesterol who take aspirin to reduce their risk of heart attack may not be protected. The study, by researchers at the University of Maryland School of Medicine, is published in the January 11, 2003, issue of the British Medical Journal.
Aspirin therapy is often prescribed for people who have had a previous heart attack to prevent a second attack, as well as for those at increased risk for a heart attack or other heart problems. The therapy is aimed at platelets, blood cells that aid in clotting after a wound or cut to the skin. Aspirin inhibits platelets from becoming unusually sticky and forming clumps that can obstruct blood flow and cause a heart attack.
"We've taken aspirin's effects for granted," says the study's senior author, Michael Miller, M.D., director of preventive cardiology at the University of Maryland Medical Center and associate professor of medicine and epidemiology and preventive medicine at the University of Maryland School of Medicine. "But there may be cause for concern for individuals with high cholesterol levels who are being assured that all they need to do is take aspirin to be protected."
The study focused on 56 people recruited from the University of Maryland Preventive Cardiology Outpatient Center who had varying degrees of elevated cholesterol levels. The mean age was 54.3 years. Three-fourths of the volunteers were men. Patients were eligible for the study if they were taking one adult aspirin per day (325 milligrams) and had a history of coronary heart disease or at least two risk factors for coronary heart disease. High cholesterol was defined as a level of 240 milligrams per deciliter (mg/dL) or higher.
The researchers tested blood samples with a special time-sensitive assay test that must be performed within four hours to determine if the platelets are responding to the aspirin. Poor platelet responsiveness was defined as clumping of more than 50 percent of the platelets. The 14 patients with the poorest response had significantly higher concentrations of total cholesterol and LDL cholesterol (the so-called "bad" cholesterol) than the people with good responses. The average cholesterol level among poor responders was 240 mg/dL compared with 186 mg/dL for normal responders. Eighty-six percent of patients with poor response were taking drugs to lower their cholesterol.
Dr. Miller says most doctors do not test platelet response to aspirin in patients on a routine basis, mainly because there is not a quick, inexpensive way to assess it. Yet with other medications, measurements are used to gauge the effectiveness of a given treatment, such as blood pressure readings, or blood sugar levels. Dr. Miller says the results of the study raise questions for additional research, including whether patients who respond poorly to the usual dosage of aspirin may need higher doses, whether they should take alternative antiplatelet agents or make further reductions in their total cholesterol and LDL cholesterol so that the aspirin may protect them.
"Until we get additional data, my suggestion for people with high cholesterol levels is to work more to get those levels down," says Dr. Miller, "either through changes in their diet, increased exercise or more potent cholesterol-lowering medications."
Dr. Miller points out that aspirin worked well for one in three people in the study, despite their elevated cholesterol levels. He says some of these people may be adhering to a diet that causes platelets to be less likely to clump together, such as one high in fish.
"If you eat a diet high in saturated and trans fats, which are commonly found in fatty red meats, donuts and cakes, these fats tend to cause the platelets to clump together," he says. Exercise and lifestyle changes may also have a positive effect on platelets, according to Dr. Miller.
Co-investigators in the study are Maribeth Friend, a graduate student, and Ivana Vucenik, Ph.D., associate professor of medical and research technology at the University of Maryland School of Medicine. Funding was provided in part by the National Institutes of Health and a Veteran's Affairs Merit Award to Dr. Miller.
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