The findings, published in Alzheimer's & Dementia: The Journal of the Alzheimer's Association, were based on genetic data from more than 13,500 participants in the landmark ASPREE Trial (Aspirin in Reducing Events in the Elderly). Scientists examined whether differences in participants' genes could help explain why aspirin might affect dementia risk differently from one person to another.

Aspirin Linked to 70% Lower Dementia Risk in Certain People

The most striking results involved genes associated with platelet count. Platelets are small components of the blood that help form clots, and researchers wanted to determine whether genetic variations related to platelet levels could influence aspirin's potential effects on dementia.

After assigning participants genetic scores associated with platelet count, the team compared dementia rates among those who received aspirin and those given a placebo.

Among people in the highest 20 percent of platelet count genetic scores, just 1 percent of aspirin users developed dementia, compared with 3.3 percent of participants taking a placebo. That difference translates to approximately a 70 percent lower relative risk of dementia among those receiving aspirin.

However, the apparent benefit was accompanied by a significant safety concern. In the same genetic group, 4.4 percent of aspirin users experienced major bleeding, compared with 2.1 percent of those receiving a placebo.

A Genetic Clue Could Change Dementia Prevention

Lead author Dr. Peter Fransquet, a Research Fellow at Monash's School of Public Health and Preventive Medicine, said the results suggest that a person's genetic makeup could eventually play an important role in determining which dementia prevention strategies are most appropriate.

"Previous trials found aspirin didn't prevent dementia when everyone was considered together," Dr. Fransquet said.

"Our findings suggest there may be more to the story.

"In people with this particular genetic profile, we saw substantially fewer cases of dementia among those taking aspirin.

"It raises the possibility that genetics could one day help us identify who may benefit from a preventive treatment, rather than taking a one-size-fits-all approach."

The possibility of more targeted prevention is especially important as dementia becomes increasingly common. Dementia Australia estimates that approximately 446,500 people in Australia are living with the condition in 2026. That number is expected to exceed one million by 2065.

Blood Platelets Reveal an Unexpected Dementia Connection

Previous research has connected dementia with platelet activation and aggregation, the processes through which platelets become active and stick together. However, scientists have had a less complete understanding of how a person's overall platelet count might relate to dementia.

The new findings point toward platelet biology as a potentially important area of investigation. Notably, the genetic association identified by researchers did not involve the well-established genetic risk factors typically linked to Alzheimer's disease and other forms of dementia.

"What's particularly interesting is that the signal wasn't linked to the established genetic risk factors for Alzheimer's disease and dementia," Dr. Fransquet said.

"Instead, it's pointing us towards platelet biology and gives us a new avenue to investigate."

Why More Research Is Needed Before Taking Aspirin

Although the findings suggest that aspirin could have different effects depending on a person's genes, researchers emphasize that the results must be confirmed before they can guide medical recommendations.

The next step is to investigate whether the association appears in other populations. Scientists would then need to conduct a clinical trial specifically involving people with the genetic profile identified in the analysis.

"We now need to confirm the finding in other studies and ultimately test it in a trial designed specifically for people with this genetic profile.

"People shouldn't start taking aspirin to prevent dementia on the basis of this study without consulting with their doctor, particularly given the increased risk of serious bleeding.

"If it holds up, the fact that aspirin is already cheap and widely available could make personalized dementia prevention a real possibility."