Impact of obesity and metabolic health status in the development of non-alcoholic fatty liver disease (NAFLD): A United Kingdom population-based cohort study using the health improvement network (THIN).

Background: With the obesity epidemic reaching crisis levels, there has been attention around those who may be resilient to the effects of obesity, termed metabolically healthy obesity (MHO), who initially present without associated metabolic abnormalities. Few longitudinal studies have explored the relationship between MHO and non-alcoholic fatty liver disease (NAFLD), which we address using over 4 million primary care patient records.
Methods: A retrospective population-based longitudinal cohort was conducted using The Health Improvement Network (THIN) database incorporating adults with no history of NAFLD or alcohol excess at baseline. Individuals were classified according to BMI category and metabolic abnormalities (diabetes, hypertension and dyslipidaemia). Diagnosis of NAFLD during follow-up was the primary outcome measure. NAFLD was identified by Read codes.
Results: During a median follow-up period of 4.7 years, 12,867 (0.3%) incident cases of NAFLD were recorded in the cohort of 4,121,049 individuals. Compared to individuals with normal weight and no metabolic abnormalities, equivalent individuals who were overweight, or obese were at significantly greater risk of incident NAFLD (Adjusted HR 3.32 (95%CI 2.98-3.49), and 6.92 (6.40-7.48, respectively). Metabolic risk factors further increased risk, including in those with normal weight and 1 (2.27, 1.97-2.61) or = < 2 (2.39, 1.99-2.87) metabolic abnormalities.
Conclusions: MHO individuals are at greater risk of developing NAFLD compared to those with normal weight. This finding supports that the MHO phenotype is a temporary state, and weight must be considered a risk factor even before other risk factors develop. Being normal weight with metabolic abnormalities was also associated with risk of NAFLD.