U-shaped associations between body mass index and serum liver enzyme levels

Liver enzymes are associated with liver function, but their relationship with body mass index (BMI) remains unclear. This cross-sectional study aimed to identify correlations between serum liver enzyme levels and BMI in the general population. The data were derived from the Dryad Digital Repository. Smooth curve and multiple linear regression analyses were performed to evaluate the associations between BMI and serum liver enzyme levels. A total of 15,464 participants, including 8430 males (54.5%), were included in the study, with a median age of 43.7 years. Smooth curve regression revealed that BMI followed U-shaped curves with respect to serum levels of liver enzymes (AST, ALT, and GGT). For AST serum levels, the turning points were BMI = 19.0 and 23.3 kg/m²; for ALT serum levels, the inflection points were BMI = 19.0 and 23.1 kg/m²; and for GGT serum levels, the inflection point was BMI = 19.5 kg/m². In addition, stratified analysis revealed that sex, fatty liver, and smoking status as covariates modified the associations between BMI and AST and ALT serum levels in participants with higher BMIs (all interactions P < 0.01). Specifically, in the higher BMI range, the positive associations between BMI and liver enzymes were more robust in men (AST and ALT), participants with fatty liver disease (AST and ALT), and participants with a history of smoking (AST, ALT, and GGT). Interestingly, alcohol consumption modified the association between BMI and GGT serum levels, regardless of BMI. Our study is the first to identify a U-shaped association between BMI and serum levels of liver enzymes in the general population, which suggests a new target for regulating liver enzyme levels.