Aspirin is a bad bargain for healthy women trying to stave off heart attacks or strokes, although it's commonly used for that purpose, according to Dutch researchers.
In a new report, they say 50 women will need to take the medication for 10 years for just one to be helped – and that's assuming they are at high risk to begin with.
"There are very few women who actually benefit," said Dr Jannick Dorresteijn of University Medical Center Utrecht in The Netherlands. "If you don't want to treat 49 patients for nothing to benefit one, you shouldn't treat anyone with aspirin."
The new study adds to a long-standing controversy over use of aspirin for primary prevention. "We all appreciate that the average treatment effect is very small, but that some patients may benefit more than others," Dr Dorresteijn said.
The Dutch findings, published in the European Heart Journal, suggest many women would still be taking the drug needlessly.
Dr Dorresteijn and his colleagues analysed data on nearly 28,000 healthy women age 45 and above who had received either low-dose aspirin or placebo in an earlier US trial.
Overall, aspirin cut the rate of heart attacks, strokes and death from heart disease from 2.4% to 2.2%.
"Nine out of 10 women experience less than a one-percent risk reduction for cardiovascular disease in the next ten years, so that is a really small treatment effect," said Dr Dorresteijn.
After subtracting the serious side effects from the health gains, the Dutch team found doctors would have to be willing to treat a lot of women to get a net advantage.
"Women older than 65 years of age benefit more than average, but still for those women the benefit was so small that you would need to treat 49 for nothing to prevent one event," said Dr Dorresteijn. "Of course it's disappointing, because you would like a medication to be effective."
Earlier this year, two large reviews of previous aspirin trials yielded similarly sobering results. One found a tiny reduction in heart attacks with aspirin and no effect on death rates or strokes. The other showed as many as 1,111 men and women would need to take aspirin daily for the duration of the trials to prevent just one death.
The US Preventive Services Task Force advises that men age 45 to 79 take aspirin to stave off heart attacks, as long as the benefit outweighs the risk of bleeding. For women age 55 to 79, aspirin is recommended to prevent strokes, with the same caveat.
Dr Michael LeFevre of the USPSTF said he wasn't surprised by the Dutch findings, but added that it muddied the potential benefit on stroke by including heart attacks in the analysis.
The number of women who would need to be treated with aspirin to prevent a stroke depends on their baseline risk. If you are willing to treat only 50 women to see a net benefit for one -- that is, taking into account serious bleeds – a woman's baseline 10-year stroke risk would have to be as high as 19%.
"So if that is our threshold, almost no women will qualify," Dr LeFevre said in an email, noting that treating 1,000 such women in their 60s will prevent 32 strokes and cause 12 bleeding ulcers.
"The central message of this study is really that there are an awful lot of women who are taking aspirin for prevention who should not be taking aspirin," he said. "I think the task force would agree with that."
(Reuters Health, Frederik Joelving, November 2011)