BACKGROUND/AIM Metabolic dysfunction is emerging as a significant risk factor for atrial fibrillation (AF) and serves as a foundational component of both metabolic dysfunction-associated steatotic liver disease (MASLD) and MASLD with moderate alcohol intake (MetALD). As the prevalence of steatotic liver disease (SLD) rises among young adults, clarifying its association with AF in this population has become a clinical priority. Accordingly, we aimed to investigate the link between different SLD subtypes and the risk of incident AF in young adults.

METHODS In this nationwide cohort study, we analyzed data from the Korean National Health Insurance Service and included individuals aged 20-39 years who underwent health screening examinations between 2009 and 2012. The participants were categorized into either the non-SLD group or the SLD group, which was defined by a fatty liver index ≥ 30. SLD was further subclassified into MASLD, MetALD, and alcohol-associated liver disease (ALD) for analysis. The risk of incident AF was evaluated using Cox proportional hazards models.

RESULTS A total of 6,375,710 young adults (mean age 30.9 years; 59.4% male) were included, with a median follow-up period of 10.6 years. The prevalence of SLD was 27.8%, which included cases of MASLD (81.7%), MetALD (13.5%), and ALD (4.7%). The risk of incident AF was significantly elevated in individuals with SLD, with progressive increases across MASLD, MetALD, and ALD subtypes. Compared with those of the non-SLD group, the adjusted hazard ratios for AF were 1.09 (95% confidence interval [CI], 1.05-1.31) in the MASLD group, 1.29 (95% CI, 1.22-1.36) in the MetALD group, and 1.52 (95% CI, 1.41-1.65) in the ALD group.

CONCLUSION SLD is associated with new-onset AF, with a progressively increased risk across MASLD, MetALD, and ALD subtypes in young adults. Given the modifiable nature of these risks, early interventions are essential to prevent long-term cardiovascular complications and reduce the future disease burden.