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Evidence Summary

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In people who do not have cardiovascular disease, aspirin does not reduce risk for death but does increase major bleeding

Mahmoud AN, Gad MM, Elgendy AY, et al. Efficacy and safety of aspirin for primary prevention of cardiovascular events: a meta-analysis and trial sequential analysis of randomized controlled trials. Eur Heart J. 2019;40:607-17.

Review questions

In people who do not have cardiovascular disease, does aspirin reduce risk for death? Does it increase bleeding events?

Background

Aspirin is often taken by people who have had a heart attack or stroke to prevent these events from happening again. When blood clots form inside the vessels that take blood to your heart or your brain, blood flow is reduced; this can lead to a heart attack or stroke. Aspirin works by reducing your blood’s ability to clot.

For years, doctors have recommended that some older adults who have never had a heart attack or stroke take an aspirin a day to prevent these events. However, aspirin can cause bleeding, and it wasn’t clear if taking aspirin daily causes more harm than good.

This review looks at whether aspirin reduces deaths and increases major bleeding in people who do not have cardiovascular disease (e.g., a history of heart attack, stroke, or blood clots in the arteries in their legs).

How the review was done

The researchers did a systematic review of studies available up to September 2018. They found 11 randomized controlled trials that included 157,248 people with an average age of 61 years. About half of the people in the studies were women.

The key features of the studies were:

  • people did not have cardiovascular disease at the start of the studies;
  • most trials used aspirin at a dose of 75 to 100 mg/day;
  • most trials compared aspirin with placebo; some compared aspirin with another group that didn’t get aspirin; and
  • people were followed for an average of 6.6 years.

What the researchers found

Compared with placebo or no treatment, aspirin

  • increased bleeding inside the skull or brain and other major bleeding;
  • reduced risk for heart attacks; and
  • did not affect risks for death or stroke.

Conclusions

In people who do not have cardiovascular disease, aspirin does not reduce risk for death but does increase risk for major bleeding compared with placebo or no aspirin treatment. It is important to recognize that these results do not apply to people who have a history of heart disease or stroke.

Aspirin vs control* in people who do not have cardiovascular disease

Outcomes

Number of trials and people

Rate of events with aspirin

Rate of events with control

Effect of aspirin at an average 6.6 years of follow-up

Death from any cause

11 trials (157,248 people)

4.6%

4.7%

No difference in effect†

Death from a cardiovascular cause‡

11 trials (157,248 people)

1.3%

1.4%

No difference in effect†

Heart attack

11 trials (157,248 people)

1.9%

2.2%

About 3 fewer people out of 1000 had a heart attack

Stroke

11 trials (157,248 people)

1.7%

1.8%

No difference in effect†

Major bleeding

11 trials (157,248 people)

1.8%

1.2%

About 6 more people out of 1000 had a major bleed

Intracranial bleeding§

11 trials (157,248 people)

0.4%

0.3%

About 1 more person out of 1000 had an intracranial bleed

*Placebo or no aspirin treatment.

†Although the rates for the 2 groups look a little different, the differences were not statistically significant. This means that the differences could simply be due to chance rather than due to the different treatments.

‡Includes sudden cardiac death and death because of heart attacks, strokes, and other heart diseases.

§Bleeding inside the skull or brain.

 




Glossary

Placebo
A harmless, inactive, and simulated treatment.
Randomized controlled trials
Studies where people are assigned to one of the treatments purely by chance.
Systematic review
A comprehensive evaluation of the available research evidence on a particular topic.
Vascular
The body's network of blood vessels. It includes the arteries, veins, and capillaries that carry blood to and from the heart.

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