Higher fatty liver index is associated with increased risk of incident atrial fibrillation in adults with diabetes: a prospective UK biobank study

Whether hepatic steatosis, as indexed by the fatty liver index (FLI), is associated with incident atrial fibrillation (AF) among adults with diabetes beyond shared cardiometabolic risk factors remains uncertain. To investigate the association between fatty liver index and incident atrial fibrillation in adults with diabetes. We analyzed 29,341 UK Biobank participants with baseline diabetes and no history of atrial fibrillation or atrial flutter, and no prior cardiovascular disease. FLI was evaluated both categorically (< 30, 30–59, 60–89, ≥ 90) and continuously using restricted cubic splines. Incident AF was identified through linked health records, with death treated as a competing risk. Cox models were sequentially adjusted for demographics, lifestyle, socioeconomic status, and metabolic factors; Fine–Gray models were also applied. Sensitivity analyses included 1:10 propensity score matching (FLI ≥ 60 vs. < 60). Among participants with FLI ≥ 30, AF risk was further stratified by the number of metabolic abnormalities (hypertension, obesity, dyslipidemia), grouped as 0, 1, 2, or ≥ 3. Over a median follow-up of 14.1 years (13.4–14.7), 2,890 incident AF events occurred. AF incidence rose across FLI categories, from 4.88 (95% CI: 4.21–5.63) to 9.92 (95% CI: 9.38–10.48) per 1,000 person-years comparing FLI < 30 with FLI ≥ 90, an absolute difference of 5.04 (95% CI: 4.15–5.92). In fully adjusted Cox models, FLI ≥ 90 was associated with a higher AF risk (HR 1.64, 95% CI: 1.40–1.92; p < 0.001), with attenuated estimates for intermediate FLI groups and a significant trend across categories (p < 0.001). Among individuals with FLI ≥ 30, AF risk increased stepwise with the number of metabolic abnormalities. Spline analyses showed a nonlinear association (p < 0.001), with AF risk increasing more noticeably at higher FLI values, particularly in the very high range. Among adults with diabetes, higher FLI was associated with a greater risk of incident AF after adjustment for measured demographic, lifestyle, and cardiometabolic factors, with the strongest association observed at very high FLI levels. These findings suggest that FLI may serve as an accessible marker for risk stratification in this high-risk population; however, residual confounding cannot be excluded and clinical utility for decision-making requires further validation.