"It means millions of healthy older people around the world who are taking low dose aspirin without a medical reason, may be doing so unnecessarily, because the study showed no overall benefit to offset the risk of bleeding", McNeil added. "It is to the great credit to the US NIH and the Australian NHMRC that they recognised this need and underwrote the substantial cost of undertaking a study of this magnitude".
"This gives pause and a reason for older people and their physician to think carefully about the decision whether to take low-dose aspirin regularly or not", Hadley says.
The study involved more than 19,000 people ages 65 and older in the United States and Australia.
"The use of low-dose aspirin resulted in a significantly higher risk of major hemorrhage and did not result in a significantly lower risk of cardiovascular disease than placebo", the researchers wrote in one of the papers.
This protective capacity of aspirin was extrapolated to people who were otherwise healthy to prevent a first heart attack or stroke, despite the evidence supporting this to be sparse.
Daily aspirin is recommended for people between 50 and 69 if they are at increased risk of heart disease, according to the U.S. Preventive Services Task Force, a guideline-setting expert panel.
"This study shows why it is so important to conduct this type of research so that we can gain a fuller picture of aspirin's benefits and risks among healthy older persons", Richard Hodes, director of the National Institute on Aging, said in a statement. In the new study, most volunteers fell into that category and aspirin didn't seem to help them.
In addition, those who took aspirin had a slightly higher likelihood of dying over the course of the study (5.9 percent) than those who took the placebo (5.2 percent).
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People were recruited between 2010 and 2014, and had to be free of dementia, physical disability or any medical condition that would require aspirin use. The difference was attributed nearly entirely to cancer, a leading killer of older people, and not internal bleeding.
Of the aspirin-takers, 3.8% experienced serious bleeding compared to 2.8% in the placebo group.
There was also an increase in cancer deaths in the aspirin-treated group, which surprised the researchers.
The team explains that this is a study looking at people over 70 who were taking aspirin to prevent the first attack and did not include those individuals who were taking aspirin after their first heart attack or stroke on medical advice to prevent a second attack. However, the higher death rate was due to more cancer deaths in the aspirin group, which could have been due to chance, the researchers said. "It is possible pre-existing cancers may have interacted with the aspirin".
The results - which show that risks of major bleeding in low-dose aspirin users overwhelm any heart benefits - were reported online in the New England Journal of Medicine and presented Sunday at the European Respiratory Society International Congress in Paris. ASPREE has provided this answer.
The researchers are continuing to follow the health of the participants to determine whether beneficial effects of aspirin, such as cancer prevention, emerge sometime after taking the drug.
However anybody who is taking aspirin should speak to their prescriber before ceasing the medication, says AMA president Dr Tony Bartone.
Big changes have occurred in preventive medicine since the original aspirin research was done, Michos told NBC News in an email. Blood clots can form when an artery is narrowed by cholesterol.