A nationwide survey of the association between nonalcoholic fatty liver disease and the incidence of asthma in Korean adults

Background Asthma and nonalcoholic fatty liver disease (NAFLD) are chronic diseases known to be associated with metabolic abnormalities. We aimed to clarify the association between NAFLD and asthma incidence in a large population-based cohort. Methods and findings We selected 160,603 individuals without comorbidities from the National Health Insurance Service-National Sample cohort between 2009 and 2014. NAFLD was defined using a surrogate marker, fatty liver index (FLI). During a median of 5.08 years' follow-up, 16,377 subjects (10.2%) were newly diagnosed with asthma and categorized into three groups according to FLI. The cumulative incidence of asthma was higher in subjects with higher vs. lower FLIs (FLI < 30, 10.1%; 30 <= FLI < 60, 10.8%; FLI >= 60, 10.5%). Higher FLI was associated with an increased incidence of asthma (Hazard ratios (HR)(highest vs. lowest FLI), 1.25; 95% CI, 1.15-1.36). The results using another definition of NAFLD, as measured by the hepatic steatosis index (HSI), were similar to the primary results. This association was more pronounced in women than in men (HR 1.46; 95% CI, 1.13-1.64 vs. HR 1.07; 95% CI, 0.94-1.20). Conclusions This study demonstrated that NAFLD, as measured by FLI and HSI, may influence the incidence rates of asthma in adults, especially in women.