A report from the US Preventive Services Task Force (USPSTF) showed that daily aspirin in people without a history of heart disease will prevent heart attacks in men, and strokes in women. In both groups the benefit of heart attack or stroke prevention needs to be weighed against the risk of gastrointestinal bleeding. The guidelines state that men over 45 and women over 55 should take a daily aspirin. And that noone over 80 should take aspirin. The investigators concluded that aspirin doses of greater than 100 mg per day (i.e. more than baby aspirin) did not add additional benefit.
An analysis of the published literature of people without heart disease examined a total of 51,342 women and 44,114 men from a range of studies who did not have heart disease but had risk factors for heart disease (Berger et al 2006). Daily aspirin in women reduced cardiovascular disease by 12%, which was statistically significant, with a 17% reduction in stroke and no effect on heart attacks or cardiovascular mortality.
These are the kind of numbers that drug companies like to throw around to scare people into buying their drugs. But the fact is that a 12% reduction is no bigee. Say you had 10 people get a heart attack out of 10,000. And then you gave all 10,000 people a pill and came back a few years later and found that only 9 of them had a heart attack. Doesn’t sound very impressive, now, does it? And yet that is your “10% reduction in heart attacks.” Oh, brother. Any you made all those people take pills for all those years for that? And what were the risks of the pills?
However for any given woman, the absolute risk reduction, or how much the risk of heart attack was reduced in that individual, was only 0.3% over a six year period. And aspirin increased the risk of major bleeding by 68%. For men there was a 14% reduction of cardiovascular events primarily related to a 32% reduction in heart attacks with no effect on strokes or cardiovascular mortality. That translated into a .37% absolute reduction over a six year period. And men had a 72% increase in major bleeding. Aspirin did not save any lives in men or women. And as pointed out by Mrs. Bremner for every stroke in women or heart attack in men that is prevented by aspirin, there is one major gastrointestinal bleeding event caused by aspirin.
For men with a history of heart disease, taking baby aspirin every day can reduce your risk of death from heart disease by about 17% (ATC 2002). Translated, this means you are reducing your risk by about 1% per year. Although technically the risk of stomach bleeding is outweighed by the heart benefits of aspirin (which can only be shown when large numbers of patients are studied), in terms of what that means to you the differences are clinically meaningless.
In patients with strokes or transient ischemic attacks (TIAs) aspirin plus dipyridamole (a blood vessel dilator) was shown to be associated with a 13% rate of cardiovascular event compared to 16% on aspirin alone, a difference that was statistically significant (Esprit 2006).
Overall, I think aspirin for disease prevention is a bunch of hooey invented by cardiologists. My father almost died from bleeding from taking aspirin for such a purpose.
A friend of mine used the aspirin story to illustrate how incredibly weak some clinical trial data really was.
ATC (2002): Antithrombotic Trialists’ Collaboration: Collaborative meta-analysis of randomised trials of antiplatelet therapy for prevention of death, myocardial infarction, and stroke in high risk patients. British Medical Journal 324:71-86.
Berger JS, Roncaglioni MC, Avanzini F, Pangrazzi I, Tognoni G, Brown DL (2006): Aspirin for the primary prevention of cardiovascular events in women and men: A sex-specific meta-analysis of randomized controlled trials. Journal of the American Medical Association 295:306-313.
Esprit (2006): Aspirin plus dipyridamole versus aspirin alone after cerebral ischaemia of arterial origin (ESPRIT): randomised controlled trial. The Lancet 367:1665-1673.
Hat tip to CDC Mole.
