Low dose aspirin helps prevent ischaemic stroke in womenBMJ 2005; 330 doi: https://doi.org/10.1136/bmj.330.7491.558 (Published 10 March 2005) Cite this as: BMJ 2005;330:558
A large study examining the benefits of low dose aspirin in the primary prevention of cardiovascular disease in women found no significant benefit in the reduction of heart attacks or death from cardiovascular causes, but a significant benefit in the reduction of ischaemic stroke. The findings, which were presented at the American College of Cardiology meeting in Florida this week, are available online (http://content.nejm.org/cgi/content/abstract/NEJMoa050613) and will be published in the New England Journal of Medicine on 31 March.
The researchers randomised 39 876 healthy women aged 45 years or older to receive 100 mg of aspirin every other day, or placebo, and then monitored them for 10 years for a first major cardiovascular event (that is, non-fatal myocardial infarction, non-fatal stroke, or death from cardiovascular causes).
The study, led by Dr Paul Ridker of the division of cardiovascular medicine at Harvard's Brigham and Women's Hospital in Boston, Massachusetts, was designed to evaluate the lowest dose of aspirin that would have a cardioprotective effect, while minimising gastrointestinal side effects by using a low dose and only on every other day. From September 1992 to May 1995, invitation questionnaires were sent to more than 1.7 million women health professionals. A total of 453 787 completed the questionnaires, with 65 169 initially willing and eligible to enrol.
During the follow-up period, 477 major cardiovascular events were confirmed in the aspirin group, compared with 522 in the placebo group, representing a non-significant reduction in risk with aspirin of 9% (relative risk 0.91; 95% confidence interval 0.80 to 1.03; P=0.13). Compared with placebo, aspirin had no significant effect on the risk of fatal or non-fatal heart attacks (1.02; 0.84 to 1.25; P=0.83) or death from cardiovascular causes (0.95; 0.74 to 1.22; P=0.68). Subgroup analyses showed that aspirin significantly reduced the risk of major cardiovascular events and ischaemic stroke among women aged 65 years or older: in the aspirin group, there were 131 major cardiovascular events (versus 175 in the placebo group) (0.74; 0.59 to 0.92) and 68 strokes (versus 86 in the placebo group) (0.78; 0.57 to 1.08).
Researchers found, however, that in the whole study group there was a 17% reduction in the risk of stroke in the aspirin group, compared with the placebo group (0.83; 0.69 to 0.99; P=0.04), owing to a 24% reduction in the risk of ischaemic stroke (0.76; 0.63 to 0.93; P=0.009) that was offset by only a small and non-significant increase in the risk of haemorrhagic stroke (1.24; 0.82 to 1.87; P=0.31).
“From a policy perspective, our findings clearly demonstrate the importance of studying women as well as men in major cardiovascular clinical trials,” the authors wrote. “An interesting finding in our subgroup analyses was that the most consistent benefit of aspirin was observed among women 65 years of age or older. This group of 4097 women composed 10% of the study population yet had almost one third of the cardiovascular events.”
In this group, aspirin use, compared with placebo use, led to 44 fewer myocardial infarctions, strokes, or deaths from cardiovascular causes (P=0.008) but to 16 more gastrointestinal haemorrhages requiring transfusion (P=0.05), “emphasizing, as with any agent, the importance of balancing benefits and risks,” the authors conclude.