Bayer began selling aspirin (acetylsalicylic acid) in 1899, and the similar salicylic acid, derived from willow bark and other sources, has been used medicinally for thousands of years. Since the 1960’s it has often been used for heart attacks and strokes. Studies showed that in patients who have had heart attacks, daily aspirin prevents another one. This is know as secondary prevention.
Doctors have assumed that it would also be good to prevent the first heart attack in patients at higher risk. This is know as primary prevention. The problem is that’s much harder to prove. Even patients at higher risk might never have one, or maybe not for many years, so a research study can take many thousands of patients followed for many years, thus costing many millions of dollars, to tell if there is a benefit. Rare side effects can take many years to figure out. There have been studies done over the years, with inconclusive and sometimes with inconsistent results.
According to a trio of recent articles (Effect of Aspirin on Cardiovascular Events and Bleeding in the Healthy Elderly, Effect of Aspirin on All-Cause Mortality in the Healthy Elderly, and Effect of Aspirin on Disability-free Survival in the Healthy Elderly), aspirin use may cause more harm than benefit for primary prevention. They looked at patients >= 70-year-old (>= 65-year-old for blacks/hispanics in the US). A low proportion of participants regularly took low-dose aspirin before entering the trial, which did not directly address whether healthy older persons who have been using aspirin for primary prevention should continue or discontinue its use. Now 2019 guidelines from the American College of Cardiology and the American Heart Association recommend low dose aspirin for primary prevention only in limited patient populations at higher risk.
When it comes to medical treatments, it’s pretty much always a question of balancing benefit versus risk and cost. For aspirin, cost is pretty much not an issue. Although studies may look at thousands of patients, people are not homogenous, and any particular study may not apply to a particular patient. The guidelines listed above state that aspirin might be considered for primary prevention in adults age 40 to 70 at higher heart risk but who do not have a higher bleeding risk. They do not recommend it for routine use for those over 70-years-old. Note that it still may be warranted in some because of higher risk, and it’s still recommended for most older patient if they have known heart disease.
I think these new recommendations will eventually lead to less patients taking aspirin to prevent a first heart attack. This will lead to less bleeding, but it may increase other problems For example, aspirin may decrease the risk of colon and other cancers. It may help prevent deep venous thrombosis (DVT) blood clots in the legs, which could lead to a more serious pulmonary embolism (PE), so long distance air travelers may be at higher risk of a clot if they stop taking their aspirin. They could just take it before a trip, but will they remember? The FDA just added a block box warning for Uloric (febuxostat), a medicine used for gout, because of recently appreciated increased risk of cardiovascular disease. Surely there will be patients on that medication on aspirin for primary prevention who will stop aspirin, as a result of reading in the media that they should, but will then go on to have a heart attack because either they didn’t discuss it with their physician, or they did but their doctor didn’t know or appreciate the increased heart attack risk with Uloric. That medicine, by the way, should also be judged on benefits versus risks and alternatives, and is still appropriate for some patients, though not as many people as the drug reps would have had doctors believe. They’ve stopped promoting it as it’s almost generic, but that’s another story.