Niha Zubair, Arivale Clinical Research Scientist, PhD
Many people take a daily baby aspirin based on evidence that suggests it can help prevent both heart disease and colorectal cancer.
This is in line with guidelines from the US Preventative Services Task Force, an independent agency that reviews scientific literature and develops clinical guidelines. Specifically, the task force recommends adults between the ages of 50 and 59 who have an increased risk of cardiovascular disease take low-dose aspirin. The recommendation for adults in this age group has a “B” rating, which suggests fairly high confidence. The same recommendation for adults between 60 and 69 only gets a “C,” and the task force does not recommend low-dose aspirin for those under 50 or over 70 because of a lack of data on safety or efficacy.
Importantly, the risks of aspirin – even at low doses – are widely recognized. The primary risks relate to bleeding, and the task force found evidence that aspirin use increases the risk of both gastrointestinal bleeding and hemorrhagic stroke. Nonetheless, for people between 50 and 59 with high cardiovascular disease risk, it felt the benefits outweighed the risks.
One study looked at the effect of low-dose aspirin on all-cause mortality, the second study looked at “disability free survival” – or healthy independent lifespan, and the third looked at cardiovascular events and bleeding-related side effects.
All three studies leveraged the same cohort of approximately 19,000 older adults in the US and Australia participating in the Aspirin in Reducing Events in the Elderly trial. Half the participants were randomized to low-dose aspirin and the other half a placebo.
Of note: To participate in the trial, adults had to be older than 70 years of age and healthy, so the study population is not the group targeted by current US Preventative Services Task Force guidelines for low-dose aspirin. In fact, as noted above, the reason the task force doesn’t make a recommendation for aspirin in this group is because of lack of evidence. These studies address that gap.
The results across the board from the three studies were not good. There was no difference in disability-free survival or cardiovascular disease between the aspirin and placebo groups, but the aspirin group had higher overall mortality (including cancer mortality) and higher rates of major bleeding, including hemorrhagic stroke.
The strengths of these three studies include the large population observed, the relatively long-term follow-up period, and access to clinical records to determine causes of death or disability. In addition, a major strength was that this was a randomized clinical trial, whereas many of the studies that have shown benefits of low-dose aspirin use were population-based observational studies.
One limitation noted by the authors is that two-thirds of the cohort had stopped the intervention (aspirin or placebo) by the end of the study, which could have reduced any benefit toward the reduction of cardiovascular disease risk. However, the fact that an increase in major bleeding events was observed in spite of this argues that participants took the aspirin long enough for it to have a biological effect.
The finding of increased cancer risk in the group assigned to aspirin therapy was a surprising one since previous studies have shown a reduced risk of cancer with low-dose aspirin. In fact, the US Preventative Services Task Force guidelines cite the benefits of aspirin in reducing colorectal cancer risk, at least in adults between 50 and 59 years old. The study’s authors state the mechanism of aspirin’s effect on cancer is not clear but note that some research suggests aspirin impacts cellular and molecular pathways related to the initiation and spread of cancer.
These three studies address an important gap in the scientific literature on the risks and benefits of low-dose aspirin in adults over the age of 70. Many millions of healthy adults currently take low-dose aspirin in the belief that it will help them avoid cardiovascular disease, even if they do not meet the current criteria for age and cardiovascular disease risk status where the most benefit is seen. This new research suggests that this decision should not be made lightly, especially in people over 70.
Given the known risks of aspirin in terms of bleeding events, the decision to take low-dose aspirin is always one that should be made in conversation with your physician and take into account your age and overall heart disease risk.
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[Arivale Hot Topics address health stories currently in the news. The Arivale Clinical Team’s commentary on these news articles is not a review of the scientific evidence, nor an endorsement of a specific study, and is not meant as official medical opinion.]