For decades, a daily dose of aspirin has been widely considered a way to protect healthy people from cardiovascular disease and even cancer. But a large international study finds that even at low doses, long-term use of aspirin may be harmful — without providing any benefit — for older people who have not already had a heart attack or stroke.

The new research reinforces the results of a study published in late August, which found that daily low-dose aspirin was too risky to be prescribed to patients at moderate risk of heart disease. In the August study and the new one, researchers found a significant risk of internal gastric bleeding caused by the medication, which thins the blood. Older patients experienced no health benefits from taking aspirin, according to the new report, published Sunday in the New England Journal of Medicine.

“We knew there would an increased risk of bleeding with aspirin, because there has always been," said study coauthor Dr. Anne Murray, a geriatrician and epidemiologist at the Hennepin Healthcare Research Institute and the University of Minnesota, Minneapolis. "But not only did it not decrease risk of disability or death, it did not decrease the risk of heart attack and stroke, and there was an increase in the rate of death."

"For healthy people 70 and older who don’t have a reason to be on aspirin, such as a previous heart attack or stroke, there was no discernible benefit."

The current guidelines recommend a daily aspirin for adults in their 50s who are at high risk of cardiovascular disease, with high blood pressure, high cholesterol or a history of smoking. The new study was designed to find out whether low-dose aspirin could prolong healthy, independent living in seniors who had not shown signs of heart disease.

"For healthy people 70 and older who don’t have a reason to be on aspirin, such as a previous heart attack or stroke, there was no discernible benefit," Murray told NBC News.

The trial followed 19,114 seniors — 2,411 from the U.S. and 16,703 Australians — for an average of 4.7 years. The minimum age was 70 for Caucasian participants and 65 for African-American and Hispanic volunteers, due to their higher risk of dementia and cardiovascular disease.

At the end of the trial, 90.3 percent of the aspirin-treated patients were still alive, compared with 90.5 percent of those who received placebos. Rates of physical disability and dementia were similar between the groups. The rates of coronary heart disease, heart attacks and strokes were also similar.

The big difference between the groups was in the rate of internal bleeding. Hemorrhagic stroke, bleeding in the brain, gastrointestinal bleeding and bleeding in other sites that required transfusion or hospitalization occurred in 361, or 3.8 percent, of participants in the aspirin-treated group and 265, or 2.7 percent, of those in the placebo group.

Rise in cancer risk?

There was also an increase in cancer deaths in the aspirin-treated group, which surprised the researchers. Previous studies have found that aspirin may be protective against certain kinds of cancer.

"There was a small increase in the number of deaths overall in the aspirin group, with the largest proportion of deaths due to cancer," said Murray. "It is possible pre-existing cancers may have interacted with the aspirin."

It may ultimately turn out that there are more benefits than risks in certain populations, said the study’s lead author, John McNeil, a professor of epidemiology at the School of Public Health and Preventive Medicine at Monash University in Melbourne, Australia.

“But we have not identified results that are strikingly different,” McNeil said in an email. Further research that may identify which groups would benefit from regular aspirin use is underway.

Dr. Erin Michos, a cardiologist, called the results "alarming," saying that aspirin should be prescribed only selectively.

Big changes have occurred in preventive medicine since the original aspirin research was done, Michos told NBC News in an email. Patients now get statins to lower cholesterol and anti-hypertensive medications to lower blood pressure.

“I think it is time we started to phase out the use of aspirin broadly for the purposes of prevention in individuals who have not had a heart attack or stroke," said Michos, director of preventive cardiology at the Ciccarone Center for the Prevention of Heart Disease at the Johns Hopkins School of Medicine.

Dr. Ravi Dave says aspirin may make sense for a small group of older healthy patients, even if they haven’t already had a heart attack or stroke, such as smokers. But for healthy patients who have not had a heart attack or stroke and who are not at high risk, “I would consider taking them off,” said Dave, director of interventional cardiology at the University of California, Los Angeles.

That’s a decision Dr. Mark Huffman plans to make in conversations with his patients.

“Some of them will say, ‘If it ain’t broke don’t fix it,’ ” predicted Huffman, an associate professor of preventive medicine at Northwestern University’s Feinberg School of Medicine and a cardiologist at Northwestern Medicine. “Others will say, ‘If the data suggest I might not have any benefit, I would like to take fewer pills.’ ”