"These findings will help inform prescribing doctors who have always been uncertain about whether to recommend aspirin to healthy patients who do not have a clear medical reason for doing so", John McNeil, head of the Department of Epidemiology and Preventive Medicine at Monash University in Australia, said in a statement.
It was first synthesised in 1898, and since the 1960s has been known to lower the risk of heart attack and stroke among those who had previously experienced heart disease or stroke.
The participants took a daily low-dose of aspirin every day for almost five years, with researchers monitoring their health and any occurrences of disease, disability or death.
Millions of healthy people take small doses of aspirin regularly in the belief that the drug will prevent heart attacks and strokes.
It was called the Aspirin In Reducing Events In The Elderly (ASPREE) trial and the results have been published in three papers in the New England Journal of Medicine.
The study was of 19,114 people in the USA and Australia in good health, with no history of heart problems and over the age of 70. The patients who took aspirin didn't report differences in dementia or physical disability compared to the control group.
Researchers found people taking the aspirin showed a significantly higher risk of bleeding, such as hemorrhages. "Aspirin is the most widely used of all preventive drugs and an answer to this question is long overdue". "Others will say, 'if the data suggest I might not have any benefit, I would like to take fewer pills'".
"The concern has been uncertainty about whether aspirin is beneficial for otherwise healthy older people without those conditions", director Dr. Richard J. Hodes of the National Institute on Aging, which partially funded the study and is part of the National Institutes of Health, said in a press release. They did, however, document a higher rate of bleeding in the group that received aspirin, compared to the group that received a placebo.
The difference was attributed nearly entirely to cancer, a leading killer of older people, and not internal bleeding.
"These findings will help inform prescribing doctors, who have always been uncertain about whether to recommend aspirin to healthy patients who do not have a clear medical reason for doing so".
The cancer finding surprised researchers because in other studies, aspirin protected against death from cancer.
The researchers point out that ASPREE's findings relate only to healthy older people, aged over 70 years, and do not apply to those taking aspirin on medical advice, for example those who have had a heart attack or stroke.
The current guidelines recommend a daily aspirin for adults in their 50s who are at high risk of cardiovascular disease, such as high blood pressure, high cholesterol or a history of smoking.
The aspirin group were also at a slightly increased risk of death.
However, the cases of major bleeding were 38 per cent more with aspirin.