The JUPITER study measured the prevalence and incidence of gastroduodenal ulcers among 187 aspirin therapy patients from Australia, the United Kingdom, Canada and Spain.
It found one in ten people taking low-dose aspirin to prevent a stroke or heart attack had a stomach ulcer at any point in time, with older patients aged 70 years and over, as well as those infected with the bacterium 'Helicobacter pylori', three times more at risk.
But despite their ulcers, the patients experienced virtually none of the expected warning symptoms, like indigestion, abdominal pain, acid reflux, nausea or bloating. In fact, their ulcers were undetected until the patients underwent an endoscopy.
The study was led by gastroenterologist, Professor Neville Yeomans - the Dean of the University of Western Sydney's Medical School.
The team also included researchers from the University of Sydney, Australia; Hospital Clinico Universitario Lozano Blesa in Zaragosa, Spain; the Mayo Clinic in Rochester, Minnesota, USA; the University of Alberta in Edmonton, Canada; pharmaceutical company, AstraZeneca in Sweden; and the University Hospital in Nottingham, UK.
Professor Yeomans says aspirin is an important treatment in patients at high-risk of heart attack, and stresses that the benefits of aspirin therapy for these patients far outweigh any side-effects. He advises concerned patients to discuss their circumstances with their GP or physician.
But he says the findings are food for thought for otherwise healthy people with low-risk or no history of vascular disease, who might see aspirin as a 'wonder drug' and are contemplating popping one every day as a simple preventative measure.
"Aspirin is a very useful, inexpensive form of therapy to help reduce the chance of heart attack or stroke among higher-risk patients. It works by helping to prevent the platelets in our blood from sticking together and forming a clot," says Professor Yeomans.
"It is particularly valuable, for example, in people who are on the verge of having a heart attack or stroke, and also valuable for reducing the risk of further cardiac events in patients. The downside is that aspirin, like most other anti-inflammatories, increases the risk of ulcers, and its blood-thinning properties can promote ulcer bleeds.
"This study reveals a high prevalence of ulcers in patients prescribed low-dose aspirin for vascular protection - doses between 75-300 mg a day.
"Other similar studies have found people taking low doses of aspirin are about two to four times more likely to be hospitalised with an ulcer bleed. What has not been quite clear is whether this is due to aspirin patients actually getting ulcers more often, or just more likely to bleed from an ulcer that might be already there."
In this study, patients underwent an endoscopy at the beginning of the trial and again three months later.
Also recorded were the patients' age and gender, duration and dose of their aspirin therapy, smoking and ulcer history, and whether the patients were infected with the ulcer-causing bacterium, 'Helicobacter pylori' - discovered by Drs Warren and Marshall of Perth, announced as recipients of the 2005 Nobel Prize for Medicine.
The results of the first endoscopy revealed 20 patients, or 10.7 per cent of the group, had ulcers - seven from Melbourne, seven from Sydney, and six from Zaragoza. None were detected in Edmonton, where 'H.pylori' infection was found to be much lower.
Of the 113 patients who were ulcer-free at the start, a further eight, or 7.1 per cent of the group, had developed an ulcer in the three months - two in Edmonton, one in Melbourne, three in Nottingham, and two in Zaragoza.
Yet only four of the 20 baseline ulcer patients reported experiencing any ulcer-like symptoms. Similarly after three months, only half of the eight patients said they had mild-to-moderate warning signs.
"It will be surprising to many that there was little difference between the ulcer and non-ulcer groups in the frequency and severity of their symptoms," explains Professor Yeomans.
"However, it fits with other research into patients who develop ulcers on this class of drugs. In fact, at baseline, more patients without ulcers reported experiencing gastric burning, discomfort or pain than those who actually had ulcers; which shows just how difficult it is to diagnose ulcers.
"The fact that there can often be no indications of an ulcer in a patient is something that needs to be remembered when prescribing aspirin as a form of preventative therapy, and patients and doctors need to be alert to any signs of ulcer complications such as bleeding.
"Aspirin can be of great benefit to those at high risk of a heart attack or stroke, but the risks as well as the benefits need to be carefully weighed before embarking on its long-term use in people who are at only low cardiovascular risk."
Results from the JUPITER study are published in the international journal, 'Alimentary Pharmacology and Therapeutics'.
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