LONDON (Reuters) - People who are aged 75 or older and take aspirin daily to ward off heart attacks face a significantly elevated risk of serious or even fatal bleeding and should be given heartburn drugs to minimize the danger, a 10-year study has found.

Between 40 percent and 60 percent of over-75s in Europe and the United States take aspirin every day, previous studies have estimated, but the implications of long-term use in older people have remained unclear until now because most clinical trials involve patients under 75.

The study published on Wednesday, however, was split equally between over-75s and younger patients, examining a total of 3,166 Britons who had suffered a heart attack or stroke and were taking blood-thinning medication to prevent a recurrence.

Researchers emphasized that the findings did not mean that older patients should stop taking aspirin. Instead, they recommend broad use of proton pump inhibitor heartburn drugs such as omeprazole, which can cut the risk of upper gastrointestinal bleeding by 70-90 percent.

While aspirin -- invented by Bayer in 1897 and now widely available over the counter -- is generally viewed as harmless, bleeding has long been a recognized hazard.

Peter Rothwell, one of the study authors, said that taking anti-platelet drugs such as aspirin prevented a fifth of recurrent heart attacks and strokes but also led to about 3,000 excess-bleeding deaths annually in Britain alone.

The majority of these were in people aged over 75.

“In people under 75 the benefits of taking aspirin for secondary prevention after a heart attack or stroke clearly outweigh the relatively small risk of bleeding. These people needn’t worry,” Rothwell said.

“In the over-75s the risk of a serious bleed is higher, but the key point is that this risk is substantially preventable by taking proton pump inhibitors alongside aspirin.”

Faculty of Pharmaceutical Medicine President Alan Boyd, who was not involved in the study, said it had been considered that the benefits of aspirin outweighed the risks of bleeding in all patients and that the new research would force a reappraisal.

Rothwell, Director of the Centre for Prevention of Stroke and Dementia at Oxford University, and his colleagues found that the annual rate of life-threatening or fatal bleeds was less than 0.5 percent in under-65s, rising to 1.5 percent for those aged 75-84 and nearly 2.5 percent for over-85s.

Because the majority of patients studied were taking low-dose aspirin, rather than more modern anti-platelet drugs such as clopidogrel or AstraZeneca’s Brilinta, the study could not draw conclusions about combined drug use.

However, a commentary in The Lancet medical journal, where the study was published, noted that patients on dual anti-platelet therapy were known to have a higher risk of bleeding than those on monotherapy and that the research showed the need for regular evaluation of older patients.