Temporal relationship between hepatic steatosis and fasting blood glucose elevation: a longitudinal analysis from China and UK

The link between nonalcoholic fatty liver disease and type 2 diabetes has not been fully established. We investigated the temporal relationship between nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes (T2D), quantitatively assessed the impact, and evaluated the related mediation effect.

This study involved participants from the China Multi-Ethnic Cohort Study and the UK Biobank. We performed cross-lagged path analysis to compare the relative magnitude of the effects between NAFLD and T2D using two-period biochemical data. Hepatic steatosis and fasting blood glucose elevation (FBG) represented NAFLD and T2D respectively. We fitted two separate Cox proportional-hazards models to evaluate the influence of hepatic steatosis on T2D. Furthermore, we applied the difference method to assess mediation effects.

In cross-lagged path analyses, the path coefficients from baseline hepatic steatosis to first repeat FBG (β_CMEC = 0.068, β_UK−Biobank = 0.033) were significantly greater than the path coefficients from baseline FBG to first repeat hepatic steatosis (β_CMEC = 0.027, β_UK−Biobank = -0.01). Individuals with hepatic steatosis have a risk of T2D that is roughly three times higher than those without the condition (HR = 3.478 [3.314, 3.650]). Hepatic steatosis mediated approximately 69.514% of the total effect between obesity and follow-up T2D.

Our findings contribute to determining the sequential relationship between NAFLD and T2D in the causal pathway, highlighting that the dominant pathway in the relationship between these two early stages of diseases was the one from hepatic steatosis to fasting blood glucose elevation. Individuals having NAFLD face a significantly increased risk of T2D and require long-term monitoring of their glucose status as well.