Daily aspirin did not prevent dementia in older adults overall, but people with one genetic profile tied to higher platelet counts had markedly lower dementia rates while taking it, according to a reanalysis of the ASPREE trial in Alzheimer's & Dementia. In that group, 1% of aspirin users developed dementia, compared with 3.3% of those on placebo.

The same group paid a price — major bleeding occurred in 4.4% of aspirin users, versus 2.1% on placebo, roughly double. That tradeoff is as important as the headline benefit.

The study, led by Monash University researchers in Australia, appeared in late September and drew renewed attention after a ScienceDaily summary on Oct. 25. It points toward personalized prevention, but it is not a reason to start taking aspirin.

Averages Hid a Subgroup Signal

ASPREE, short for Aspirin in Reducing Events in the Elderly, was a large placebo-controlled trial of daily low-dose aspirin, 100 milligrams, in more than 19,000 healthy older adults in Australia and the United States, most aged 70 or older. Its main results, published in 2018, found aspirin did not extend healthy, disability-free life and raised the risk of major bleeding. Later analyses found it did not prevent dementia when all participants were considered together.

That result matched a broader shift in medical advice. Daily aspirin is no longer routinely recommended for older adults who have not had a heart attack or stroke, because bleeding risks can outweigh benefits.

"People shouldn't start taking aspirin to prevent dementia on the basis of this study," lead author Peter Fransquet of Monash's School of Public Health and Preventive Medicine said, adding that people should consult their doctor.

The new analysis asked a different question: could a benefit be hidden inside a subgroup that the overall average masks? Averages can bury effects that help some people while doing nothing, or harm, in others.

A Platelet Score Changes the Picture

The team calculated polygenic scores, which combine many small genetic variants, linked to platelet count in more than 13,500 ASPREE participants. Platelets are blood cells involved in clotting, and earlier research has linked platelet activation to dementia.

Among people in the top 20% of platelet-count genetic scores, aspirin was associated with about a 70% lower relative risk of dementia, according to Monash University. In absolute terms, that is about 2.3 fewer cases per 100 people.

The math on the other side is striking. Bleeding rose by about 2.3 cases per 100 people in the same group, almost exactly matching the dementia difference. That means, on these numbers, aspirin traded roughly one fewer dementia case for roughly one extra major bleed. Whether that trade is worth it depends on the severity of each outcome and a person's own health, a judgment only a doctor and patient can make.

Notably, the signal did not involve established Alzheimer's risk genes, which the authors say points to platelet biology as a possible pathway. Fransquet said genetics could one day help identify who may benefit from preventive treatment.

Bleeding Risk Carries Equal Weight

Aspirin thins the blood, which is why it raises bleeding risk, including in the stomach and brain. In the high-platelet-score group, major bleeding roughly doubled. For an older adult, a serious bleed can mean hospitalization, disability, or death.

Thomas Holland, a physician scientist at Rush University who was not involved in the study, told Newsweek that aspirin is "by no means a benign medication." He also described the platelet explanation as a proposed mechanism, not a proven one.

Evidence Limits and Practical Advice

This was a secondary analysis of an existing trial, not a trial designed to test aspirin in this genetic group. Subgroup findings can appear by chance, and the public summaries do not report the subgroup size, number of dementia cases, or confidence intervals. The authors say the result needs confirmation in other populations and in a dedicated trial.

The study also does not offer a clinical test. Platelet-count polygenic scores are research tools, not routine lab results, so people cannot currently learn whether they fall into this group through a standard checkup.

Who should pay attention? Older adults already taking aspirin, people with a family history of dementia, and those with bleeding risks such as stomach ulcers, kidney disease or blood thinner use. Anyone taking aspirin should not stop or start it without medical advice, since it may have been prescribed for heart protection.

Dementia is common, which is why the finding drew attention. Newsweek cited an estimate that 42% of Americans over 55 will eventually develop dementia. Still, a subgroup result from one trial cannot change prevention guidance on its own.

Proven ways to support brain health remain the same, including controlling blood pressure, staying physically active, protecting hearing, avoiding smoking and managing diabetes. Talk with a doctor about personal risk, including family history and current medications.

The research team includes ASPREE leaders John McNeil and Paul Lacaze of Monash, whose group has used the trial's genetic data to study how inherited risk shapes responses to common drugs.

Next, researchers would need to run a trial in people with high platelet-count genetic scores to see whether the benefit holds and outweighs bleeding. Nature World News will report any follow-up studies.

The bottom line: aspirin did not prevent dementia across the board, but one genetic group showed lower dementia rates — and double the major bleeding. The finding is an early clue for personalized prevention, not a recommendation to take aspirin.

What Readers Want to Know

Does aspirin prevent dementia? Not for older adults overall. A benefit appeared only in one genetic subgroup.

Who appeared to benefit? People in the top 20% of platelet-count genetic scores, where 1% on aspirin developed dementia versus 3.3% on placebo.

What is the downside? Major bleeding roughly doubled in that group, from 2.1% to 4.4%.

Can I get tested for this genetic score? Not through routine care. The score is currently a research tool.

Should I start taking aspirin? No, not without talking to your doctor. The study's authors say it is not a basis for starting aspirin.

What happens next? A dedicated trial in people with this genetic profile would be needed to confirm the finding.