Many people take aspirin daily for its blood-thinning properties, which help protect against strokes and heart attacks. But those same properties can also pose risks, increasing the danger of gastrointestinal bleeding. Because current U.S. guidelines on daily aspirin use would recommend aspirin for many older people, researchers in Australia used a computer simulation to find out whether aspirin would be likely to do more harm than good.

What the researchers wanted to know: What are the implications of daily low-dose aspirin use in people age 70 and over?

What they did: The researchers developed a computer model to look at what might happen in a hypothetical population of older people if low-dose aspirin use (about 75-150 milligrams a day) is routine. They started with 10,000 men and 10,000 women aged 70-74 who had not had heart attacks or strokes and followed them until they died or turned 100. The simulated people's health status was based on people in Victoria, Australia, aged 70 to 74 in 2000. The researchers programmed in the probabilities of diseases, based on age and sex, and the computer used those to determine each person's chance of being sick or dying each year. They used data on how aspirin affects the risk of heart attack, stroke, and major internal bleeding to estimate who would have those problems. The model even incorporated a prediction that the population gets healthier over time, just like in the real world, so people in the model became less likely to die of stroke over time, for example. The researchers ran the simulation thousands of times, to get a range of possible outcomes.

What they found: Taking aspirin daily did reduce heart attacks and strokes, but those gains were offset by the increase of gastrointestinal bleeding and hemorrhagic stroke.

What the study means to you: For healthy older people—none of the simulated people in this study had had strokes or heart attacks when the simulation started—prescribing daily aspirin may do more harm than good. Actual studies on humans would be needed to clear up the risks and benefits of aspirin. In the meantime, the researchers say this should remind doctors to be cautious when prescribing any medicines, keeping in mind that their adverse effects may outweigh their benefits.

Caveats: This is a computer model, not real life. That means it's entirely dependent on the researchers' assumptions, the rates and probabilities they used in the program.

Find out more: Read drug information about aspirin from the National Library of Medicine

Read the article: Nelson, M.R., et al. "Epidemiological Modeling of Routine Use of Low Dose Aspirin for the Primary Prevention of Coronary Heart Disease and Stroke in those Aged >=70." British Medical Journal. Published online May 20, 2005.

Abstract online: http://bmj.bmjjournals.com