A new analysis of data from a large clinical trial of healthy older adults found higher rates of brain bleeding among those who took daily low-dose aspirin, and no significant protection against stroke.

The analysis, published Wednesday in the medical journal JAMA, is the latest evidence that low-dose aspirin, which slows the clotting action of platelets, may not be appropriate for people who do not have any history of heart conditions or warning signs of stroke. Older people prone to falls, which can cause brain bleeds, should be particularly cautious about taking aspirin, the findings suggest.

The new data supports the recommendation of the U.S. Preventive Services Task Force, finalized last year, that low-dose aspirin should not be prescribed for preventing a first heart attack or stroke in healthy older adults.

“We can be very emphatic that healthy people who are not on aspirin and do not have multiple risk factors should not be starting it now,” said Dr. Randall Stafford, a medical professor and epidemiologist at Stanford University who was not involved in the study.

He acknowledged, however, that the decision was less clear-cut for people who did not fit that description.

“The longer you’ve been on aspirin and the more risk factors you have for heart attacks and strokes, the murkier it gets,” he said.

For most people who have already had a heart attack or stroke, daily aspirin should remain an important part of their care, a number of cardiac and stroke experts said in interviews.

The new analysis used data from Aspirin in Reducing Events in the Elderly, or ASPREE, a randomized control trial of daily low-dose aspirin among people living in Australia and the United States. The 19,114 participants were adults over 70 who were free of any symptomatic cardiovascular disease. (Any person with a history of stroke or heart attack was excluded from the study.)

It aimed to reveal nuances in the data to address the difficult balance that doctors face in preventing clots and bleeds in older patients. The rationale was that the balance of risk and benefits of aspirin might shift as people age. Strokes become more frequent from clots as well as from small blood vessels that become more fragile over time, and older people can experience an increased likelihood of head trauma from falls.

The study randomly assigned 9,525 people to take 100 milligram daily doses of aspirin and 9,589 people to take matching placebo pills. Neither of the groups nor the researchers knew who was taking each type of pill. The study followed participants for a median of 4.7 years.

Aspirin appeared to reduce the occurrence of ischemic stroke, or a clot in a vessel supplying blood to the brain, though not significantly. Researchers found a significant increase — 38 percent — of intracranial bleeding among the people who took daily aspirin compared with those who took a daily placebo pill.

Cardiologists who were not involved in the study lauded its size and rigorous design, in which specialists reviewed medical records and characterized the events manually, rather than relying on outcomes reported by the patients. But they noted that the rate of strokes was low in both groups, making the results difficult to extrapolate. The paper did not include an analysis on heart attacks.

They also questioned how the findings would apply to the diverse population of the United States, since a majority of participants were in Australia, and 91 percent of them were white.

In the past, some doctors regarded aspirin as something of a wonder drug, capable of protecting healthy patients against a future heart attack or stroke. But recent studies have shown that the powerful drug has limited protective power among people who have not yet had such an event, and it comes with dangerous side effects.

The U.S. Preventive Services Task Force recommended last year that most people who have never had a heart attack or stroke not begin taking low-dose aspirin because of the risk of internal bleeding. The American College of Cardiology quickly released a follow-up statement, reiterating that the recommendation “does not apply to patients with a prior history of heart attack, stroke, bypass surgery, or recent stent procedure.”

Still, some stroke patients seemed to misinterpret the guidance. In interviews, multiple cardiologists said that patients who clearly needed aspirin had abruptly stopped taking it, only to end up in the emergency room with a second stroke.

No one should ever stop taking aspirin without consulting a doctor, they said.

“When a study comes out, you have to ask yourself, how well do I fit into this study’s population?” said Dr. Shlee S. Song, the director of the Comprehensive Stroke and Telestroke Programs at Cedars-Sinai. “If you’ve ever had a heart attack or stroke event, this study’s findings do not apply to you.”

In an interview last year, Dr. Song, who oversees stroke programs at four hospitals in Los Angeles, urged patients not to abandon the drug. She said this study had not changed her opinion.

“There is a lot of noise out there,” she said. “At the end of the day, these things will need to be discussed with a doctor who knows your specific story.”

Dr. Joshua Willey, an associate professor of neurology and a stroke specialist at the Columbia University Vagelos College of Physicians and Surgeons, said the risk-benefit calculation would also differ for each patient, depending on how long they had been on aspirin and why their doctor recommended the pill in the first place. For a patient at high risk of another condition, like colorectal cancer, a doctor might conclude that aspirin offers protective power that offsets the patient’s risk of bleeding.

For patients who need to remain on aspirin, he said, the study findings have a different significance for doctors: “Check their balance, get them physical therapy, make sure the house is set up properly. Do everything you can in that Medicare age group to mitigate the risk of a fall.”


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