May 19, 2005 -- Low-dose aspirin helps prevent heart attacks and strokes from occurring in people at high risk. But do the risks of aspirin therapy outweigh the benefits in the elderly? An Australian researcher thinks they might, and he says a large clinical trial is needed to find out.
Epidemiologist Mark R. Nelson, PhD, of Monash University in Melbourne, Australia, tells WebMD that the increased risk of potentially life-threatening bleeding in people over 70 who take low-dose aspirin daily may be greater than the heart disease protection offered by the therapy.
A statistical model he developed suggests that this is the case, but Nelson says an actual study involving large numbers of elderly people must be done to back up the theory.
"The most important thing to stress is that people who are taking aspirin therapy under their physician's supervision should not stop," he says. "The benefits of aspirin are clear for people with a history of heart disease. But they are not so clear for aged people without known heart problems."
The uncertainty about the risks and benefits of aspirin in older people without heart disease stems from the fact that the elderly are often excluded from clinical trials, Nelson says.
Studies conducted primarily in people in their 50s and 60s overwhelmingly show that low-dose aspirin therapy (75 to 150 milligrams per day) provides benefits for those at risk for heart disease. Those benefits include reducing the risk of heart attacks and ministrokes. Aspirin prevents blood from clotting by blocking the production of a key chemical. This prevents clots from decreasing blood flow, the cause of heart attacks and some strokes.
Since age is the strongest predictor of cardiovascular risk, the thinking has been that the benefits of aspirin therapy are even greater in the elderly than in people who are middle aged.
But older age is also a strong risk factor for bleeding from aspirin use. Even low-dose aspirin can increase the risk of bleeding in the gut. Since the elderly are underrepresented in clinical trials, the extent to which this risk influences the benefits of aspirin treatment is not well understood, Nelson says.
Heart Protection vs. Bleeding Risk
Nelson's model estimated the impact of the routine use of low-dose aspirin in 20,000 people without heart disease between the ages of 70 and 74.
The model suggested that heart disease protection gained from low-dose aspirin use may be offset by serious cases of bleeding. Nelson and colleagues write that the overall balance of harm and benefit "could tip either way."
"Despite sound evidence for efficacy, the temptation to blindly implement low-dose aspirin treatment for the primary prevention of [stroke and heart disease] in elderly people must be resisted," they add.
Time for a Big Study?
But cardiologist Donald W. LaVan, MD, says he strongly believes that aspirin therapy benefits the elderly. He says most of his older patients take a daily aspirin and identifying those who should not due to an increased risk of bleeding is not a problem.
LaVan is a clinical associate professor of medicine at the University of Pennsylvania and a spokesman for the American Heart Association.
"The vast majority of people over 70 that I see have some underlying cardiovascular problem," he tells WebMD.
Although he agrees that the elderly are underrepresented in clinical trials, LaVan does not agree that a large study of the magnitude that Nelson is proposing is needed.
Nelson puts the cost of such a study at $30 million and says he is searching for funding.