By Susan Scutti, CNN

(CNN) -- Aspirin, a mild pain reliever, is one of the most familiar medicines in the world. One increasingly common use of this popular medicine, though, may not be safe for some older adults, a new analysis of existing research suggests.

People without heart trouble who took a daily low-dose aspirin had a lower risk of heart attack, stroke and death; however, the modest benefits gained were balanced by a major risk, research published Tuesday in the journal JAMA showed. The daily dose increased their risk of bleeding in the gut or in the skull.

"This calls into question the net benefit of taking aspirin, and whether people who have not previously had cardiovascular disease should take aspirin," Dr. Sean Zheng, lead author of the study and an academic clinical fellow in cardiology at King's College Hospital in London, wrote in an email.

Aspirin-a-day is controversial, not recommended for everyone

Low-dose aspirin taken daily is often recommended for people with heart trouble, despite the known risks of gastrointestinal or intracranial bleeding. Scientific studies have shown aspirin's proven benefit in helping prevent a second heart attack or stroke in such high-risk patients.

However, controversy surrounds the use of aspirin to prevent a first heart attack or stroke in low risk patients. The US Preventive Services Task Force, for example, recommends that some older patients without heart trouble take a daily low-dose aspirin, while the European Society of Cardiology does not.

Past clinical trials, some conducted in the 1980s, have shown "conflicting findings," Zheng noted, and since then, the practice of medicine has changed and public awareness of the benefits of exercise and ills of smoking has increased. By including the newest research in its analysis, the new study sought "to provide a more relevant estimate of the benefits and risks of aspirin," he explained.

Data for the analysis came from 13 studies with a combined total of 164,225 participants, all without cardiovascular disease. These studies compared using aspirin versus not using aspirin in people without cardiovascular disease.

Aspirin use was associated with a 0.38% absolute risk reduction for heart attack and stroke and a 0.47% increased absolute risk of major bleeding, the researchers found.

What does this mean in real-world terms?

"For every 265 patients treated with aspirin for 5 years, one heart attack, stroke or death from cardiovascular disease would be prevented," said Zheng, who is a practicing physician. "On the other hand, for every 210 patients treated with aspirin over the same period, one would have a serious bleeding event."

Aspirin also showed no link to premature death for any reason, including a cardiovascular event, and it did not increase the risk of cancer or cancer death, the study found.

The study's findings are not really 'new'

Donna Arnett, past president of the American Heart Association and dean of the College of Public Health at the University of Kentucky, wrote in an email that the "findings aren't really new, but rather, confirmatory of the prior meta-analyses."

Arnett, who was not involved in the study, suggested that patients should discuss with their doctors "their level of risk for a cardiovascular event and determine if there are other interventions that might be more useful, such as quitting smoking or lowering blood pressure or cholesterol levels." She also cautioned that patients with any history of bleeding abnormalities should speak to their physician about using aspirin.

In an editorial, Dr. J. Michael Gaziano, a preventive cardiologist at VA Boston Healthcare System and professor of Medicine at Harvard Medical School, praised the new research as "well conducted." Although the conclusions may not be "new," Zheng's study demonstrates that there is "a general consistency" among both old and the most recent findings.

"When applying these results to an individual patient, clinicians must consider other interventions in addition to aspirin, such as smoking cessation and control of blood pressure and lipid levels, to lower risk," wrote Gaziano, who took no part in the analysis. He noted that "risk is not static" and if patients stop smoking, adopt a healthier lifestyle, and manage their lipids and blood pressure, the risk of a cardiovascular event declines.

"Because weighing the risks and benefits of aspirin in primary prevention is complicated, it should involve a shared decision-making discussion between the patient and the clinician," he said.

Aspirin's benefits as a primary prevention likely overstated

Dr. John McNeil, a professor in the Department of Epidemiology and Preventive Medicine at Monash University's School of Public Health and Preventive Medicine in Australia, said "it is likely" that the new study slightly overstated the benefits of aspirin to prevent a first stroke or heart attack.

This is due to the fact that Zheng and his co-author "averaged trials undertaken 20-30 years ago (which were very favorable to aspirin) with more recent trials which have been substantially less favorable" while also including "four 'unblinded studies' which generally provide less reliable evidence," explained McNeil, who conducted one of the underlying studies, though he did not perform the analysis.

McNeil's own research, the ASPREE trial, looked at the value of taking an aspirin a day to prevent heart attack or stroke in people over the age of 70. "The results were quite unequivocal," he said. "Aspirin confers no overall benefit in this age group and there was a suggestion of net harm."

Other recent studies, McNeil said, "also failed to identify a substantial benefit from aspirin in primary prevention in special groups. Further work is ongoing to determine whether there are any subgroups who might benefit."

Ultimately, McNeilsaid, the new work "provides little support for the widespread use of aspirin for the average person" to prevent a heart attack or stroke, though this is "not to be confused" with the established benefit for at risk patients.