Healthy women may not benefit from prophylactic aspirin

Low-dose aspirin taken by healthy women to prevent heart attack and stroke may be ineffective or even harmful, a new study suggests. Even among high-risk women, 50 would need to take aspirin for 10 years to benefit 1 woman, researchers report online November 16 in the European Heart Journal.

Investigators from University Medical Center Utrecht, the Netherlands, and Harvard Medical School, Boston, analyzed data from the Women’s Health Study on 27,939 initially healthy women 45 years of age and older who had been randomized to receive either aspirin (mostly 100 mg every other day) or placebo.

Aspirin treatment over 10 years lowered the absolute risk of a major cardiovascular event by less than 1% in more than 90% of study participants. Age was the strongest predictor of treatment effect, with women older than 65 deriving greater benefit than younger women. Current smoking and baseline risk of cardiovascular events weren’t positively associated with treatment effect.

Women with a predicted absolute treatment effect of 2% or more had a mean age of 69.4 years compared with 54.7 years in the total study population, and 99.2% of women younger than 65 years had a predicted absolute treatment effect ≤2%.

“Aspirin was ineffective or even harmful in the majority of study participants,” the authors conclude. “Despite higher effectiveness in women ≥65 years of age, the 10-year number willing to treat (NWT) still needs to be well above 50 for the benefits to outweigh the harm of treatment.”  When the NWT to prevent 1 major cardiovascular event in 10 years is 50 or lower, the best primary prevention strategy for women is no aspirin treatment, they say.

Ongoing randomized trials, including two evaluating the effectiveness of aspirin in patients 65 years and older, may shed further light on the role of aspirin in primary prevention, the researchers note.

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