The following article was published on The Conversation.

Monday’s medical myth: take an aspirin a day after you turn 50

By Michael Tam, University of New South Wales

Aspirin is a historical marvel. It’s been manufactured for more than a century and is still in widespread use. No other medication can claim as many different narratives and uses as this analgesic – it’s been known as:

• A traditional medicine – aspirin-like treatments, based on salicylate, have been derived from plants such as willows for millennia
• An international blockbuster – at the turn of the twentieth century, aspirin was one of the few effective treatments for fever and pain, and was wildly popular (and profitable)
• A hazard to children – aspirin was recognised in the 1980s as a potential cause of childhood death
• A modern wonder-drug – aspirin has been resurrected as an important and inexpensive medication for the prevention and treatment of heart attacks and strokes.

And there are many fascinating tales of intrigue, international politics and corporate espionage in aspirin’s history.

German affiliates undermined the manufacture of explosives in the United States during World War I by cornering the market of a key ingredient, under the guise of aspirin production. And Germany was forced to hand over the trademark “Aspirin” as part of war reparations in the Treaty of Versailles.

In the modern context, it is commonly believed that once individuals reach a certain age, it’s wise to take “an aspirin a day” for good health.

This narrative starts in 1948 with Dr Lawrence Craven, a general practitioner, in California. He had observed that aspirin was a mild blood thinner and reasoned that it might be able to prevent heart attacks.

Dr Craven enrolled his male patients, aged 40 to 65, into a clinical trial and asked them to take aspirin daily. In the 1950s, he published three articles on his trial and concluded that aspirin appeared to protect his patients from heart attacks and strokes.

Dr Craven died in 1957 (of a heart attack!) and his results – which were published in the obscure Mississippi Valley Medical Journal – were promptly forgotten.

How aspirin works in clotting and bleeding was discovered in the 1960s. And by the 70s and 80s, aspirin was tested in clinical trials for heart attacks and strokes. These studies demonstrated that aspirin was effective in preventing further heart attacks or strokes (known as secondary prevention).

In the 1990s, our “medical myth” was not considered a myth. The American College of Chest Physicians (ACCP), a respected group that publishes guidelines on the use of blood thinners, recommended that aspirin “be considered for all individuals over age 50 years who are free of contraindications”.

But others were less confident about such a broad recommendation. Firstly, although aspirin is unambiguously beneficial for those who already had cardiovascular disease, the evidence was less clear for those who did not (such use is known as primary prevention).

Secondly, long-term aspirin therapy has potential harms – it increases the risk of bleeding, which, in some cases, can be life-threatening. Conceptually, if an individual’s risk of cardiovascular disease is low, then the potential benefit of aspirin would not outweigh the potential harms from bleeding.

The most recent recommendations from the ACCP (published February 2012) are a “soft” suggestion for aspirin for primary prevention in those aged 50 years and above. It recognises that the benefits to heart attacks and strokes are closely matched with the risk of major bleeding.

The authors were swayed by some recent data suggesting aspirin might lower cancer risk and death. Nevertheless, they emphasised the need for shared decision making between doctors and patients.

So, is that the end of this particular aspirin narrative?

Not quite. In keeping with the drama of the history of aspirin, a major study examining the role of aspirin in primary prevention was published in the same month as the ACCP guidelines. It confirmed that the benefits of lowering heart attacks and strokes were similar to the increased risks of bleeding.

Importantly, the study found no reduced risk of cancer, which is contrary to previous reports.

Behind this lack of clarity is the uncertainty of small numbers – trying to balance a small gain with a small risk. For someone who has never had a heart attack or stroke, the likelihood of benefit from aspirin is low, but the payoff could be massive. Similarly, the odds of being harmed by aspirin are also low, but could be catastrophic if it occurred.

Those aged over 50 years without a history of cardiovascular disease may benefit from regular low-dose aspirin. But that depends on their individual risk (and perceptions of risk) of heart attack, stroke and major bleeding.

So before you pick up the aspirin for your daily dose, talk to your GP about the potential risks and benefits for you.

Michael Tam is a community general practitioner and discusses issues surrounding cardiovascular risk, and its prevention with patients. He otherwise does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.

This article was originally published at The Conversation.
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