Does Low-Dose Aspirin Prevent Heart Attacks? An Evidence-Based Review

The short answer

Yes, low-dose aspirin significantly prevents recurrent heart attacks in individuals with a history of cardiovascular events (secondary prevention). However, for healthy individuals without established cardiovascular disease, the evidence does not support routine low-dose aspirin for primary prevention due to an unfavourable risk-benefit profile, primarily driven by an increased risk of serious bleeding.

What the evidence actually shows

The efficacy of low-dose aspirin in cardiovascular disease prevention is bifurcated into secondary and primary prevention. For secondary prevention, the evidence is unequivocal and robust (Tier I). A meta-analysis by the Antithrombotic Trialists' Collaboration (2002) of 287 studies involving over 200,000 patients demonstrated that antiplatelet therapy, predominantly aspirin, reduced the risk of serious vascular events (non-fatal myocardial infarction, non-fatal stroke, or vascular death) by about one-quarter in patients with a history of such events. This benefit is considered a cornerstone of post-event care.

Conversely, for primary prevention in individuals without established cardiovascular disease, the picture is far less clear. Multiple large-scale randomised controlled trials (RCTs) have investigated this. The ARRIVE trial (Gaziano et al., 2018) in individuals with moderate cardiovascular risk found no significant reduction in the primary endpoint of cardiovascular events with aspirin compared to placebo. Similarly, the ASCEND trial (Bowman et al., 2018) in diabetic patients without established cardiovascular disease showed a reduction in serious vascular events but a corresponding increase in major bleeding. The ASPREE trial (McNeil et al., 2018) in healthy older adults found no benefit in disability-free survival and an increased risk of major haemorrhage.

Antiplatelet therapy reduces the risk of serious vascular events by about one-quarter among high-risk patients.

— Antithrombotic Trialists' Collaboration, BMJ 2002

Where Harvard Health gets it right

Harvard Health publications often correctly emphasise the established role of low-dose aspirin in secondary prevention. They typically advise that individuals who have already experienced a heart attack, stroke, or have undergone procedures like angioplasty or bypass surgery should continue aspirin therapy as prescribed by their physician. This aligns perfectly with the overwhelming Tier I evidence showing a significant reduction in recurrent events in this high-risk population. They also generally acknowledge the bleeding risks associated with aspirin, which is a crucial consideration for any patient.

Where the evidence is more nuanced

Harvard Health, like many general health communicators, sometimes struggles to convey the precise nuance of primary prevention. While they may mention the declining recommendations for aspirin in this group, the emphasis on the 'potential' benefits can sometimes overshadow the critical finding that for most healthy individuals, these potential benefits are outweighed by the increased risk of major bleeding, particularly gastrointestinal and intracranial haemorrhage. The concept of 'intermediate risk' individuals, for whom some guidelines previously suggested aspirin, has largely dissolved under the weight of recent large RCTs, which have failed to demonstrate a net clinical benefit. The threshold for benefit in primary prevention is exceptionally high and rarely met in contemporary populations.

Practical implications

For individuals with a documented history of heart attack, stroke, or peripheral artery disease, low-dose aspirin remains a critical component of their treatment regimen, offering substantial protection against future events. This is a decision made in consultation with a healthcare professional. However, if you are a healthy individual without a history of cardiovascular disease, the evidence strongly suggests that initiating low-dose aspirin for primary prevention is not beneficial and carries undue risk. Lifestyle modifications, such as a balanced diet, regular exercise, maintaining a healthy weight, and smoking cessation, offer a more profound and safer approach to cardiovascular health for the vast majority of the population.

Where reasonable people still disagree

• The optimal risk stratification tools for identifying a very small subset of individuals who might still benefit from primary prevention aspirin, even with a higher bleeding risk.
• The long-term implications of aspirin use on cancer prevention, as some studies suggest a reduced risk of certain cancers, particularly colorectal cancer, with prolonged use.
• Whether specific genetic predispositions to bleeding or thrombotic events might alter the risk-benefit profile for certain individuals, necessitating personalised recommendations.