BACKGROUND Nonalcoholic fatty liver disease (NAFLD) is associated with an increased risk of diabetes but has been rarely investigated in young adults. In this study, we investigated the relationship between NAFLD and incident diabetes risk in young adults using nationwide Korean population data.

METHODS This population-based cohort study from the Korean National Health Insurance Service included adults aged 20 through 39 years who underwent a health examination from 2009 to 2012. NAFLD was defined as a fatty liver index (FLI) ≥60 in the absence of alcohol consumption of ≥30 g/day. Newly diagnosed diabetes during follow-up was identified using claims data. Cox regression was used to calculate the hazard ratio for incident diabetes after adjusting for classical confounders.

FINDINGS Among the 5,254,786 participants, 9.3% had an FLI ≥60. During the median follow-up of 8.6 years, 91,885 cases of incident diabetes occurred. In multivariable analysis, the risk of incident diabetes was significantly higher in the NAFLD group than the control group (adjusted hazard ratio = 4.97, 95% confidence interval, 4.90-5.05). Stratified analyses showed higher associations in those who were ≥30 years, male, obese, smokers, alcohol consumers, and did not regularly exercise (all P < 0.001).

CONCLUSIONS NAFLD is associated with a five-fold increased risk of incident diabetes in young adults. These results suggest an independent high risk for incident diabetes in young adults and underscore the importance of paying early attention to patients who develop NAFLD before middle age.