In recent years, researchers have gained a deeper understanding of the effects of low-dose aspirin for the prevention of cardiovascular disease. It now appears that aspirin has different effects in men and women.

Among men, the benefits of aspirin are well documented. It has been shown to reduce the risk of first and second incidents of heart attack, while its effect on stroke prevention is less certain. If chewed within 30 minutes of the onset of a heart attack, aspirin has also been shown to reduce the damage to the heart muscle. Based on these findings, many leading medical groups, including the American Heart Association, recommended that aspirin therapy also be considered for prevention of heart disease among women in certain circumstances.

Until recently, however, there were few studies examining aspirin’s ability to protect women from cardiovascular events. In 2005, the results of the Women’s Health Study were released. This 10-year study examined low-dose aspirin use among nearly 40,000 women. Although smaller studies had found that aspirin was protective for men and women, the Women’s Health Study found that aspirin did not prevent first heart attacks, nonfatal stroke or death among women under the age of 65. The study did find, however, that aspirin helped prevent stroke and reduced the risk of heart attack in women over age 65.

Similarly, the study found that low-dose aspirin therapy had no effect on the risk of developing any variety of cancer among women, with the possible exception of lung cancer.

These results were generally reaffirmed by a meta-analysis published in early 2006 in the Journal of the Medical Association. To conduct a meta-analysis, researchers pool data from several existing studies. In this case, a team of researchers looked at data that included women from the Women's Health Study in addition to five other studies. In all, more than 95,000 people, including 44,114 men and 51,432 women, were enrolled in the studies. These studies found that aspirin prevents ischemic stroke in women, but had no effect on heart attacks. For men, the studies revealed that aspirin therapy reduced the risk of heart attack but did not prevent stroke.

More studies are needed to confirm these results. However, based on the uncertainty surrounding aspirin use and its possible side effects, women should not begin low-dose aspirin therapy unless under the direct supervision of a physician.

The study did not examine the effects of aspirin therapy on other conditions, such as high blood pressure that occurs during pregnancy or the use of aspirin among women who are suffering a heart attack.

Aspirin’s role in the prevention of heart attack and stroke appears to be different among men and women. Until recently, however, the extent of this difference may not have been fully appreciated.

Among men, aspirin has been shown to reduce the risk of a first heart attack and possibly reduce the risk of a first stroke (although the data on stroke among men remains mixed). Aspirin has also been shown to reduce the risk of a second heart attack and stroke and lower the risk of certain cancers among men. Based on these findings, low-dose aspirin therapy was recommended by leading organizations, including the American Heart Association, for the prevention of cardiovascular disease among high-risk women and all women over 65, regardless of risk level.

However, relatively few studies had been conducted on the role of low-dose aspirin therapy among women. In 2005, the large, multi-center Women’s Health Study was completed. This study examined the use of low-dose aspirin among nearly 40,000 women for 10 years. Among other findings, the study concluded that:

• Aspirin did not prevent first heart attacks or death from cardiovascular disease among women under the age of 65.
  
  
• Aspirin reduced the incidence of stroke by 17 percent in the study group, a statistically significant finding.
  
  
• Among women over age 65, low-dose aspirin reduced the risk of major cardiovascular events by 26 percent. However, this benefit has to be weighed against aspirin’s increased risk for bleeding.

Since these findings were published, several other studies have looked at the use of aspirin therapy in women. Among them was a meta-analysis published in early 2006 in the Journal of the Medical Association. To conduct a meta-analysis, researchers pool data from several existing studies. In this case, a team of researchers looked at data that included women from the Women's Health Study in addition to five other studies. In all, more than 95,000 people, including 44,114 men and 51,432 women, were enrolled in the studies. These studies found that aspirin prevents ischemic stroke in women, but had no effect on heart attacks. For men, the studies revealed that aspirin therapy reduced the risk of heart attack but did not prevent stroke.

The studies also shed light on the most effective dosage. In general, it appeared that low-dose aspirin (at 81 mg) was equally as effective as full-strength (352 mg) aspirin. In fact, fewer than half of women who are candidates for aspirin therapy are actually taking aspirin.

In 2007, the American Heart Association (AHA) revised its guidelines regarding the use of aspirin therapy in women. The new guidelines stress the need for a long-term approach to heart health, which may include aspirin therapy. In a departure from previous guidelines, the new guidelines suggest that women over 65 should consult their physician about starting an aspirin regimen, regardless of their risk level for heart disease.

Although aspirin is still not recommended for heart attack prevention among low-risk women under age 65, there is still plenty these women can do to reduce their risk of cardiovascular disease. Risk factor reduction includes:

• Smoking. Cigarette smoking is the leading contributor to preventable deaths in the United States. Smoking is associated with half of all heart attacks among women, and studies have shown that risk is elevated among women who smoke as few as two cigarettes a day. Quitting smoking is strongly advised for all smokers.
  
  
• Diabetes. This condition appears to be a more powerful predictor of heart disease among women than men. This could be because diabetes is more often accompanied by other risk factors, such as obesity, in women than in men. Studies have shown that only 34 percent of diabetic women regularly take aspirin, despite a 1997 recommendation by the American Diabetes Association (ADA) that aspirin therapy be considered in all high-risk adults over the age of 30 with diabetes. This recommendation was made before the findings from the Women’s Health Study were released.
  
  
• Obesity. Defined as a body mass index (BMI) greater than 30. Many studies have linked obesity, especially abdominal obesity to increased risk of heart attack and stroke. Obesity also increases the risk of developing type 2 diabetes.
  
  

• Diet. Eating a heart-healthy diet that is low in saturated fats and oils and cholesterol. This includes eating foods high in heart–healthy vitamins and minerals, including certain B-vitamins, antioxidants, calcium and magnesium. Some experts also recommend additional supplements, such as garlic. Women should be aware, however, that some dietary supplements, including vitamin E and omega-3 fatty acids, can interact with aspirin. Specific diets that are being recommended by some experts include the Mediterranean diet and the DASH diet.
  
  

• Engaging in regular exercise. Exercise is critical to maintaining a normal weight, and it helps keep the heart and arteries in better shape. Moderate physical activity is recommended for at least 30 minutes per day, seven days a week. Shorter, daily periods of exercise are also helpful.
  
  

• Controlling high blood pressure (hypertension). High blood pressure is a major risk factor for heart attack and stroke.

Although the Women's Health Study found that aspirin did not prevent heart attacks among women, the study did not evaluate the use of aspirin in ongoing heart attacks. Numerous previous studies have shown that aspirin, if taken early enough, can limit the damage caused by an ongoing heart attack in men and women.

Immediately after calling an emergency number (911 in the United States), women and men are encouraged to chew a tablet of adult aspirin (325 milligrams [mg]) or four baby aspirins (324 mg total) when having a heart attack. Chewing the aspirin causes it to reach the bloodstream more quickly than simply swallowing it.

This procedure is not recommended for people who are having a stroke until medical professionals have determined the cause of the stroke. Aspirin may worsen the damage caused by hemorrhagic strokes, or strokes caused by a ruptured blood vessel that bleeds into the brain.

Once in the bloodstream, aspirin reduces the blood’s “stickiness,” preventing the formation of additional blood clots. Fewer blood clots means less likelihood of blockages in the flow of oxygen-rich blood to the heart, which caused the heart attack in the first place. Aspirin has been found to lessen the damage of a current or past heart attack if taken either during or immediately after the attack.

Aspirin is sometimes recommended for pregnant women as a preventive measure against preeclampsia ( pregnancy-induced high blood pressure). Preeclampsia is the leading cause of maternal death. It can strike without warning.

Preeclampsia can lead to a dangerous condition called eclampsia, which is marked by convulsions, seizures and coma occurring between the 20th week of pregnancy and the first week after birth. About one in 200 pregnant patients with high blood pressure develop this condition. If left untreated, it can be fatal.

A woman is considered at high risk for preeclampsia if she has suffered from high blood pressure for at least four years before becoming pregnant.

Supporters of aspirin therapy for high-risk pregnant women believe that aspirin may help to prevent pre-eclampsia by balancing the levels of two chemicals in the body: thromboxane and prostacyclin. Critics of the therapy point out that research has not supported the routine use of aspirin for all pregnant women, particularly because of the risks associated with aspirin during pregnancy.

These risks include excessive bleeding during delivery and a greater risk of the fetus developing a heart defect called patent ductus arteriosus – a condition in which a normal fetal blood vessel called the ductus arteriosus fails to close after birth, as it normally should.

There is evidence that aspirin may reduce the risk of miscarriage in high-risk pregnancies involving in-vitro fertilization. It is also believed that aspirin may improve blood flow through the placenta and to the fetus by helping to keep the blood vessels open (dilated) and preventing obstructing blood clots from forming in the placenta.

Contrasting studies have been performed to determine which group of women, if any, would benefit from low-dose aspirin during pregnancy and when the therapy should begin. In general, researchers are united in agreement that aspirin therapy does not benefit high-risk women for preeclampsia. Beyond that, there is ongoing debate. In general, pregnant women should never begin aspirin therapy unless under direct advisement from their physician.

Aspirin therapy should be started only under the advice of a physician, and physicians generally advise against aspirin therapy for the following people:

• Pregnant women. Unless prescribed by a physician, taking aspirin is generally not a good idea during pregnancy, especially during the first and third trimesters. It can cause abnormal bleeding in the mother and/or the unborn child. Furthermore, aspirin can prolong or otherwise complicate delivery. Women who are breastfeeding are also encouraged to avoid aspirin.
  
  
• Women trying to become pregnant. Studies suggest that aspirin and other NSAIDs (nonsteroidal anti-inflammatory drugs) may be a cause of ovulation problems and infertility.
  
  
• People with heart failure. Aspirin and other blood-thinning regimens are often prescribed for these patients, but there is some indication that aspirin has no benefit for these people and may even be damaging.
  
  
• People who are going to have surgery. Aspirin can promote excessive bleeding and most surgeons request that their patients refrain from taking aspirin for several (generally 10) days before surgery.
  
  
• Children under 18 who are recovering from chickenpox or the flu. Aspirin has been linked to a rare but potentially fatal disease called Reye syndrome. For this reason, aspirin must be kept out of the reach of children.
  
  
• Heavy drinkers (three or more alcoholic drinks a day). Aspirin has been linked to stomach irritation, liver damage and excessive bleeding in these people.
  
  
• People with chronic intestinal problems, including ulcers, gastritis, inflammatory bowel disease (e.g., Crohn's disease and ulcerative colitis) and bleeding conditions.
  
  
• People taking daily doses of vitamin E, omega-3 fatty acids or certain NSAIDs. The combination of these substances may cause bleeding problems. However, many patients can be safely treated with anticoagulants and low-dose aspirin.
  
  
• People with a personal medical history or family history of cataracts. Regular use of aspirin can increase the risk of cataracts, particularly among patients under the age of 65.
  
  
• People with allergies to aspirin and certain other medications.
  
  
• People with uncontrolled high blood pressure (hypertension).

Aspirin works best with individuals whose blood pressure, cholesterol and weight levels are within the normal range. Aspirin therapy should be started only with a physician’s approval.

There are a number of side effects associated with aspirin use that have been reported in some patients. These include:

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to aspirin and women:

1. What is the benefit of my taking aspirin every day?
   
   
2. What dosage should I take? Does brand matter?
   
   
3. Does this increase my risk for other conditions in the risk/benefit analysis?
   
   
4. What happens if I miss a dose or two? Will that increase my risk for a stroke?
   
   
5. If I think I am experiencing a heart attack, should I still chew an aspirin, even though they are not recommended for prevention of heart attack in women?
   
   
6. Can I take aspirin with other drugs?
   
   
7. If my stomach is sensitive, will this dosage of aspirin cause gastrointestinal side effects?
   
   
8. Are there other drugs that have the same benefit if I cannot take aspirin?
   
   
9. Should I take the aspirin with or without food?
   
   
10. What is the connection between aspirin therapy and various forms of cancer?