Men who take low-dose apirin in the hope of preventing heart disease may be doing more harm than good, a study has found. The beneficial effects of low-dose aspirin were outweighed by the risks of bleeding in men with high blood pressure and, while greater benefits were seen in men with lower blood pressure, even in this group the risk did not necessarily outweigh the benefits (British Medical Journal 2000;321:13).
In a trial of 5,499 men aged between 45 and 69 years, Professor Thomas Meade (director, Medical Research Council epidemiology and medical care unit, Wolfson institute of preventive medicine, London) and colleagues compared the effect of low-dose (75mg) aspirin for primary prevention of coronary heart disease (CHD) and stroke with warfarin and placebo in different groups of patients.
For CHD, the results showed that, in patients with a systolic blood pressure of less than 130mmHg, treatment with aspirin gave a risk reduction of 45 per cent (relative risk 0.55). However, in patients with pressures greater than 145mmHg, aspirin gave a relative risk factor of 0.94. The authors say that this suggests "neither a beneficial or harmful effect". There were no significant differences between groups of different ages and cholesterol levels.
The study also examined the effects of aspirin treatment on stroke. Aspirin gave a relative risk of stroke of 0.41 in patients with systolic blood pressures less than 130mmHg compared with 1.42 for patients with pressures greater than 145mmHg. The combined results for CHD and stroke showed a significant increasing benefit of aspirin with lower blood pressures, the researchers say.
Self-medication with aspirin is widespread, even by many for whom there is no particular indication, the researchers add. "If our results are correct, men with pressures of about 145mmHg or more will derive little, if any, cardioprotective benefit from aspirin. They will, however, be exposed to the risk of troublesome and occasionally serious non-cerebral bleeding, even with 75mg aspirin," they conclude.
They add that, while there was still some uncertainty about the blood pressure above which aspirin use would be inadvisable, their results and the British Hypertension Society guidelines "all draw attention to the importance of satisfactory control of blood pressure for those in whom the prophylactic use of aspirin is being considered."
The study was conducted in patients taking aspirin for primary prevention of coronary disease. However, most people who have had a heart attack should take aspirin, as the benefits for them are greater, said Professor Meade (ie, for secondary prevention).
Professor Philip Bath (professor of stroke medicine, University of Nottingham) said in a press statement on behalf of the "Stop Stroke" campaign (sponsored by Boehringer Ingelheim): "There is no doubt that patients on aspirin for secondary prevention of stroke should continue with this therapy. However, this should be done on the backdrop that blood pressure is adequately controlled."
The British Heart Foundation says that the study shows that aspirin may not be a good thing for the "worried but well". Professor Charles George (medical director, BHF) commented: "Hopefully it will discourage the many worried but well from their daily quarter aspirin, which could possibly be doing more harm than good".