A new study links daily low-dose aspirin in older adults to a much lower risk of dementia. The work was published in Alzheimer’s & Dementia, the journal of the Alzheimer’s Association, and found that low-dose aspirin “could be helpful in reducing dementia risk,” according to a report by the health site Health and Me1. The report’s headline puts the lower risk at “at least 70%” and adds that “a serious complication still remains”1.
The finding stands out because the largest tests of aspirin and dementia so far, in which people were randomly given aspirin or a dummy pill, did not find a difference. This article sets out what is reported about the new study, what the earlier trials measured, and why bleeding keeps coming up.
What is known about the new study
Very little detail is available in the coverage Biohack reviewed. The report names the journal and states the general finding: lower dementia risk in older adults taking low-dose aspirin1. It does not, in the text available, describe how many people were studied, how long they were followed, what dose they took, or whether people were randomly assigned to aspirin.
That matters for how to read the “70%” figure. When researchers look back at people who chose to take aspirin and compare them with people who did not, the two groups can differ in many ways, such as overall health, access to doctors or other habits. Such studies can show a link, but not that aspirin itself lowered the risk. Until the study’s methods are clearer, the result is best read as a reported association, not a measured effect of the drug.
The biggest trial found no dementia difference
The strongest earlier evidence comes from ASPREE (Aspirin in Reducing Events in the Elderly). It was a double-blind, placebo-controlled trial, meaning neither the volunteers nor the researchers knew who got aspirin and who got an identical dummy pill2. It enrolled 19,114 older people: 16,703 in Australia and 2,411 in the United States2.
Volunteers were 70 or older, or over 65 for African-American and Hispanic people in the US. They could not have dementia or a physical disability when they joined, and were followed for an average of 4.7 years2. Half took 100 mg of aspirin a day3.
The dementia results were published in the journal Neurology in 20203. There were 575 confirmed dementia cases, and 41% were classed as probable Alzheimer’s disease3. The researchers found no substantial difference between aspirin and the dummy pill in dementia, probable Alzheimer’s, or mild cognitive impairment, an early stage of memory and thinking problems3. Changes in thinking skills over time were also similar in both groups3. The authors concluded there was “no evidence that aspirin was effective in reducing risk of dementia, MCI, or cognitive decline”3.
ASPREE’s main result, published in 2018, was that aspirin did not affect survival free of dementia or disability: 90.3% of the aspirin group and 90.5% of the dummy-pill group were alive without lasting disability or dementia at the end2. The aspirin group also had a higher death rate, 5.9% versus 5.2%, driven mainly by cancer deaths, a finding the researchers said should be read with caution2.
A second trial, in people with diabetes
A separate trial called ASCEND (A Study of Cardiovascular Events in Diabetes) included more than 15,000 adults with type 2 diabetes in the UK who had no prior heart attack, stroke or dementia4. Half took 100 mg of aspirin daily and half took a matching dummy pill, for about seven years of treatment and nearly nine years of tracking in total4.
Results presented at the American Heart Association’s 2021 meeting found that daily low-dose aspirin did not affect the risk of dementia or mental decline in this group4. The study author, Jane Armitage of the University of Oxford, explained why the question was open in the first place:
“Aspirin may be protective for dementia by preventing some strokes due to blockages, or it may increase the risk because of bleeding into the brain.”
Those results were reported as a conference presentation in that coverage4.
The bleeding problem
The Health and Me headline flags “a serious complication” without the article text Biohack read spelling it out1. In the earlier trials, the clearest measured downside was bleeding. Aspirin thins the blood, and daily use is linked to internal bleeding, including bleeds in the brain4.
In ASPREE, serious bleeding (bleeding strokes, bleeding in the brain, gut bleeding, or bleeding elsewhere that needed a transfusion or hospital stay) happened in 361 people on aspirin, or 3.8%, compared with 265 people on the dummy pill, or 2.7%2. Most of that extra bleeding was in the gut and the brain2. Major bleeding accounted for 5% of deaths in the trial2. Aspirin also did not lower major heart and stroke events in those healthy older adults: 448 people had such events on aspirin and 474 on the dummy pill, rates the researchers described as similar2.
This is why US heart guidelines are cautious. The 2019 American College of Cardiology and American Heart Association recommendations say adults without known heart disease should only take aspirin for heart attack and stroke prevention if they have the highest heart risk and a very low bleeding risk4. Draft guidance from the US Preventive Services Task Force at the time also advised against prescribing daily aspirin for prevention in adults without existing heart disease, while people with a past heart attack or stroke should keep taking it if their doctor prescribed it4.
Who is behind the research
The new study’s authors and funders were not named in the coverage Biohack reviewed1. For the earlier work, the ASPREE dementia paper was led by researchers at Monash University in Australia with US collaborators, including Raj C. Shah of the Rush Alzheimer’s Disease Center3. Projects linked to that work were funded by Australia’s National Health and Medical Research Council3. The US government’s National Institute on Aging and National Cancer Institute were involved, and their officials commented on the 2018 results2. The trial’s registry record lists Hennepin Healthcare Research Institute as sponsor5. None of these sources describe drug company funding.
What to watch next
The first thing to watch is the full paper: how many people it followed, whether they were randomly assigned to aspirin, what dose they took, and whether the authors measured bleeding alongside dementia. Those details decide how the “at least 70%” figure compares with the trials that found no effect.
The second is ASPREE’s long-term follow-up. After the trial pills stopped, participants kept their scheduled visits and calls, and an observational follow-up called ASPREE-XT began in January 2018 to look for delayed effects of aspirin, mainly on cancer, and any other lasting effects on the outcomes being tracked, which include dementia5. When the first results came out, the National Institute on Aging’s Evan Hadley said:
“Continuing follow-up of the ASPREE participants is crucial, particularly since longer term effects on risks for outcomes such as cancer and dementia may differ from those during the study to date.”
That quote is from the 2018 coverage2. For now, the best-controlled evidence in older adults shows no clear dementia benefit from daily low-dose aspirin and a measurable rise in serious bleeding234. The new study adds a reported link in the other direction, and its weight will depend on details not yet public in the coverage. This is news, not medical advice.
