New research presented at the EHRA 2025, a scientific congress of the European Society of Cardiology, shows that the presence of atrial fibrillation (AFib) increases the risk of future dementia by 21% in patients diagnosed with AFib under 70 and the risk of early-onset dementia (diagnosed before age 65 years) by 36%.

The association was stronger in younger adults and was lost in older adults aged 70 years and over.

“This is the largest European population-based study evaluating the association between AFib and dementia,” say the authors, which include Dr. Julián Rodriguez García of the Electrophysiology and Arrhythmia department of the Bellvitge University Hospital, Barcelona, Spain. “The association between AFib and dementia was stronger in patients under 70 and was maximal for early-onset dementia.”

Atrial fibrillation causes an irregular heartbeat and is relatively common, affecting 2–3% of the general population, with the prevalence rising with age.

Some studies have suggested an independent association between AFib and dementia, while others have failed to confirm this relationship. The strength of this association, as well as its interaction with stroke, remain controversial. “Identifying subgroups with the strongest association can help understand the drivers of this association and inform targeted preventive interventions,” explain the authors.

In this new study, the researchers assessed the independent association between AFib and incident dementia in Catalonia, Spain. The population-based observational study included individuals who, in 2007, were at least 45 years old and had no prior diagnosis of dementia.

The population was sourced from the System for the Development of Research in Primary Care, which provides anonymized data on over 80% of the Catalan population.

Incident dementia cases were defined using a validated approach based on International Classification of Disease 10 (ICD10) codes and prescription data for dementia-related medications. Early-onset dementia (EOD) was defined as a diagnosis occurring before age 65. The follow-up period extended over 15 years, from 2007 to 2021.

The study included 2,520,839 individuals with an average follow-up of 13 years. At baseline, 79,820 patients (3.25%) had a recorded diagnosis of AFib. In multivariable analyses adjusting for potential confounders, AFib was, overall, a statistically significant but weak predictor of dementia, linked with a 4% increased risk of dementia.

However, age was found to significantly affect the association between AFib and dementia. In prespecified analyses stratified by age, the strength of the association progressively weakened with increasing age: in patients aged 45–50, those with AFib were 3.3 times more likely to develop dementia than those without AFib. But in patients aged over 70 years, no association was found.

Further analysis shows the association lost statistical significance from 70 years. By contrast, in patients diagnosed with AFib before the age of 70, the condition independently increased the risk of dementia by 21%, and an even stronger effect was observed for early-onset dementia, with AFib increasing the risk by 36%.

Reflecting on the potential causes of the association, the authors say, “Dementia is often a multifactorial condition with mixed neuropathological findings rather than a single pathophysiological process. This may explain why AFib has a greater impact in younger patients, where it could be one of the primary pathogenic factors.

“Conversely, in older individuals, additional contributors to cognitive decline—such as age-related neurodegeneration—may lessen the relative impact of AFib.”

Sensitivity analyses that removed cases of previous stroke during follow-up yielded similar results: AFib was associated with a modest increase (6%) in the risk of dementia in the overall population, a stronger association (23% increased risk) in those diagnosed with AFib in midlife (<70 years old) and had the greatest effect towards early-onset dementia (52% increased risk).

Therefore, patients with AFib without a prior stroke still have a higher risk of dementia, with the greatest risk observed in early-onset dementia.

The authors say, “Atrial fibrillation is a risk factor for stroke and stroke is a risk factor for dementia. However, the observation that the association between AFib and dementia remains unchanged after excluding patients with prior stroke indicates that other mechanisms must be involved in the increased risk of dementia among AFib patients.

“These mechanisms may include silent strokes—meaning those that showed no clinical symptoms and can only diagnosed with CT scan or MRI—and also microinfarcts and microbleeds.”

Regarding additional potential mechanisms connecting AFib and dementia, the authors say, “Hemodynamic changes, which involve alterations in the flow and pressure of blood in the body caused by AFib, and autonomic dysregulation, which refers to an imbalance in how the body controls automatic functions like heart rate, breathing, or blood pressure, could also play a role in the disease of small blood vessels in the brain associated with dementia.

“Additionally, systemic inflammation associated with atrial fibrillation may amplify these effects, creating a synergistic pathway that further increases dementia risk.”

Overall, they conclude, “The study demonstrates a significant and strong association in younger patients between two pathologies—atrial fibrillation and dementia—that are among the major health challenges of the 21st century.

“We should now investigate whether early detection strategies and aggressive management of atrial fibrillation in younger patients can help in reducing the risk of dementia and changing the natural course of the disease.”