Harvard Women's Health Watch

Experts recommend low-dose aspirin to prevent stroke in women

Lower doses are as effective as higher doses and are likely to be safer.

Women ages 55 to 79 should consider taking a daily aspirin to reduce their risk of having a stroke, according to new guidelines from the United States Preventive Services Task Force (USPSTF), an expert panel that reviews evidence and recommends preventive health strategies. The guidelines reflect evidence showing that the cardiovascular benefits of aspirin vary by gender. Aspirin reduces women's risk for ischemic stroke, the most common kind (caused by blood clots), but not heart attacks. In men, it lowers the risk of heart attacks but not strokes.

The guidelines, which were published in the Annals of Internal Medicine (March 17, 2009), apply only to people with no history of heart disease or stroke. The USPSTF discourages aspirin therapy in women under age 55, because their risk for stroke is generally so low that the risk of aspirin-related gastrointestinal bleeding outweighs any benefit. Because evidence was lacking, the group made no recommendation for women ages 80 and over.

The panel found benefits with doses of aspirin ranging from 75 milligrams (mg) a day to 325 mg every other day. Noting that the risk of bleeding increases with higher doses, it stated that 75 mg — about the dose in a so-called baby aspirin — "seems as effective as higher doses." Baby aspirin is available over the counter.

Results differ by gender

Earlier research showed that low-dose aspirin helps prevent first heart attacks in healthy men and lowers the risk for subsequent heart attacks and strokes in women and men who've already had a cardiovascular event. Physicians routinely recommend that men take a daily baby aspirin starting in their early 40s, and many give the same advice to both women and men who have cardiovascular risk factors, such as hypertension. Many experts expected aspirin therapy to work as well for women as it does for men — cutting the risk of a first heart attack by more than a third.

Then, in 2005, came the results of the Women's Health Study (WHS). This 10-year trial, involving almost 40,000 healthy women, average age 54.6, showed that low-dose aspirin (100 mg every other day) didn't reduce their risk of a first heart attack as it does in men, but did reduce their stroke risk. (In those ages 65 and over, aspirin use resulted in fewer heart attacks as well as fewer strokes.)

Other research has corroborated the WHS findings. In 2006, for example, a reanalysis of six randomized controlled trials confirmed the gender-based difference at a wide range of doses, from 100 mg every other day to 500 mg daily. Aspirin users had a 70% greater risk of gastrointestinal bleeding, and higher rates of stomach ulcers and bruising.

Now what

Aspirin isn't entirely benign, and every woman's risk profile is different. So if you're thinking about aspirin therapy, see your clinician to discuss the potential benefits and possible risks in light of your specific situation. Also, while drugs can be useful, lifestyle provides a firmer foundation for health. In one study, women who didn't smoke, were active (or had a nonsedentary job), ate plenty of fruits and vegetables, and drank alcohol in moderation cut their risk for heart attack and stroke by more than half, compared with women who had none of these behaviors.